MICHIGAN STATE UNIVERSITY SING, MICHIGAN ABSTRACT PART I THE EFFECT OF NON-BONDED INTERACTIONS IN SOLVOLYTIC DISPLACEMENT REACTIONS PART II SOME PROTON-13c COUPLING CONSTANTS IN SUBSTITUTED ARYLCARBINYL COMPOUNDS by Stuart Edward.Scheppele The rate retardation observed upon substitution of hydrogen by deuterium beta to the leaving group in SNl reactions has.been princi- pally attributed to the greater ability of hydrogen than deuterium to hyperconjugatively stabilize the transition state (1). Recently the concept of hyperconjugation has been questioned (2). Bartell (3) has attributed the beta deuterium isotope effect to the larger steric re- quirements of the proton than the deuteron. So far it has been impos- sible to assess the contribution of non-bonded interactions to isotope effects observed in solvolytic displacement reactions. Since hypercon- jugative stabilization of the transition state is not possible, the rates of solvolysis of the following compounds were studied to ascer- tain the influence of non-bonded interactions on solvolytic deuterium. isotope effects. The 8-methyl and 8-bromo isomers of I also offered x CH 2C1 x CD 2C1 ' I C x = H, D, CH3, CD3, Br. Stuart Edward Scheppele themselves as systems to investigate rate acceleration due to steric strain (h). To insure SNl conditions the solvolyses were carried out in 0.32 m water-formic acid at 25.00h0. The rates were followed by potentiometric titration of the liberated chloride. The rate constant observed for a- naphthylcarbinyl chloride was h.h9 x 10-5 sec.-1 with an average devia— tion of i 0.11 x 10-5 sec -1. For X = H, kfi/kfil was 1.35; for X a D, kfi/k£ was 1.0. For X = Br, kér/kfi was 1.37 and for X = CH3, REES/k; was 85. Due to experimental difficulties the solvolysis rates of the remaining compounds could not be determined using the present method. The failure to observe an isotope effect (greater than h%) is at- tributed, to a first approximation, to compensatory effects in the ground and transition states. The large increase for the 8-methyl compound is attributed to a partial release in the transition state of severe ground state steric strain. The rate factor is not a true measure of this effect due to complete loss of resonance stabilization of the incipient carbonium ion in the transition state. The small increase Observed for the 8-bromo compound is attributed to an increased inductive stabilization of the ground state. Also the bromine atom, being polarizable, may be elongated~ and whittled down on the side facing the chloromethylene group, thus reducing steric strain. The second part of this thesis was concerned with investigating some factors influencing J13C-H' The isomeric xylenes, halo-toluenes, methyl- and halobenzyl alcohols were included, along with a number of naphthalene derivatives. Stuart Edward Scheppele The coupling constants were obtained at 60 Mc. from 13C natural abundance using a Varian Associates Model A-60 spectrometer. In the compounds studied non—bonded interactions have a negligible effect on the coupling. The small differences are reasonably ascribed to inductive effects. REFERENCES (1) Halevi, E. A. in "Progress in Physical Organic Chemistry," edited by S. G. Cohen, A. Streitwieser, Jr., and R. W. Taft, Vol. 1, New York: Interscience, 1963. (2) Dewar, M. J. S., "Hyperconjugation," New York: Ronald Press CO., 1962. (3) Bartell, L. S., J. Am. Chem. Soc., §3, 3567 (1961). (A) Brown, H. C. and I. Moritani, ibid., 11, 3623 (1955). PART I THE EFFECT OF NON-BONDED INTERACTIONS IN SOLVOLYTIC DISPLACEMENT REACTIONS PART II SOME PROTON—13C COUPLING CONSTANTS IN SUBSTITUTED ARYLCARBINYL COMPOUNDS BY Stuart Edward Scheppele A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 196A DEDICATION This thesis is dedicated to my wife, Judith, for her patience and encouragement in completing the experimental work and for her invaluable assistance in perfecting this manuscript. It is also dedi- cated to my parents, not merely for their financialand moral support, but for their basic belief in the values of higher education. ii ACKNOWLEDGMENT The author wishes to express his sincere appreciation to Dr. G. J. Karabatsos for his inspiration and guidance not only during the course of this investigation but also in the many esoteric matters encountered by this author in the past four years. Appreciation is extended to Dr. A. Timnick and Dr. K. 0. Stone for their many helpful discussions concerning the analytical methods, and eSpecially to Dr. Stone for use of the Karl Fischer reagents. Apprecia- tion is extended to Dr. M. E. Russell for many stimulating discussions concerning kinetic problems and derivation of rate expressions. Appreciation is extended to the National Science Foundation for financial support from September, 1961 to September, 196D. iii TABLE OF CONTENTS PART I THE EFFECT OF NON-BONDED INTERACTIONS IN SOLVOLYTIC DISPLACEMENT REACTIONS INTRODUCTION RESULTS AND DISCUSSION I. Synthesis a-Naphthylcarbinol . 8-Methyl-d-Naphthylcarbinol . 8- -Bromo-a-Naphthylcarbinol . a-Naphthylcarbinyl p-Toluenesulfonate . a-Naphthylcarbinyl 3, S— Dinitrobenzoate a-Naphthylcarbinyl p-Nitrobenzoate Arylcarbimyl Chlorides . . II. Product Studies CIW1U1CJC)UJ:> A. Methanolysis of o-Naphthylcarbinyl -Nitro- benzoate and a-Naphthylcarbinyl 3, -Dinitroa benzoate . . B. Insoluble Products Formed During SolvoLysis Of d-Naphthylcarbinyl Chloride C. Insoluble Products Formed During SOlvolysis of 8- —Methyl— a-Naphthylcarbinyl Chloride . . III. Analytical Methods for the Determination of Chloride A. Volumetric Determination of Chloride by the Volhard Method . . . . B. Determination of Chloride by Potentiometric Titration . . . IV. Kinetics . EXPERIMENTAL I. Synthesis . . . . . . . . A. Preparation ofa a-Naphthylcarbinol . . B. Preparation ofd d-Naphthylcarbinol-a ,a-dz C. Preparation ofa a-Naphthylcarbinol- -8— d . . D. Preparation ofa a-Naphthylcarbinyl p-Toluene- sulfonate . . E. Preparation ofa a-Naphthylcarbinyl péNitrObenzoate F. Preparation ofa a-Naphthylcarbinyl3 3,5 Dinitro- benzoate . . . . . . . . . . . . . . . . G. Preparation of l-Bromonaphthalene-8-d . iv Page 10 10 10 10 10 10 11 ll 12 12 12 13 17 2O 20 29 b3 68 68 68 68 68 69 70 71 Sr‘xL‘P—‘III TABLE OF CONTENTS (Cont.) Preparation Preparation Preparation Preparation Preparation Preparation Chloride . II. Product Studies of 1—Naphthoic Acid-8-d . . of a-Naphthylcarbinyl Chloride . . of a-Naphthylcarbinyl Chloride-8-d. of d-Naphthylcarbinyl Chloride-d,a-d2 of 8-Bromo-a-Naphthylcarbinyl Chloride of 8-Methyl-a-Naphthylcarbinyl A. Methanolysis of d—Naphthylcarbinyl p-Nitro- benzoate . B. Methanolysis of a-Naphthylcarbinyl 3, 5- Dinitro- benzoate . . . . C. Insoluble Products Formed During SOlvolysis of a-Naphthylcarbinyl Chloride in Aqueous H Formic Acid. . . D. Insoluble Products Formed During SOlvolysis of 8- -Methyl-a-Naphthylcarbinyl Chloride in Aqueous Formic Acid. . . . . . . . . . III. Analytic Procedures . . . . . . . . . .‘. A. Preparation of Reagents and Standard Solutions. Purification of Carbon Tetrachloride . Purification of Petroleum Ether Preparation of 1 M Potassium Chloride Preparation of POEassium Thiocyanate . Preparation of Silver Nitrate Solutions Preparation of Indicator Solutions . Preparation of Primary Standard Sodium ‘ Chloride Solutions. . Preparation of Primary Standard Silver ~ Nitrate Solutions . . . . Preparation of Sodium Chloride Solutions in Formic Acid . Preparation of Solutions of Hydrogen Chloride in Formic Acid . . . . . . . . . General Techniques . B. Calibration of Glassware C. Volhard Titrations Procedure 1 . Procedure 2 . Procedure 3 . . . . D. Potentiometric Titration Apparatus Preparation Preparation of Silver Electrode of Salt Bridges General Titration Procedures . V Page 72 73 7b 714 7b 7b 7b 7h 75 76 TABLE OF CONTENTS (Cont.) IV. Extraction Procedures A. Procedure 1 . B. Procedure 2 . V. Determination of Appearance of Turbidity in the Solvolysis of a-Naphthylcarbinyl Chloride as a Function of Concentration . . . . . . . . VI. Preparation of Aqueous Formic Acid Solvent for ' Kinetic Runs A. Purification of Formic Acid . B. Determination of the Water Content in Formic Acid . . . . . . . . . . . . . . . . . . . C. Preparation of 0.32 m Water in Formic Acid VII. Rate Determination . PART II SOME PROTON-13C COUPLING CONSTANTS IN SUBSTITUTED ARYLCARBINYL COMPOUNDS INTRODUCTION RESULTS . DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . . A. Substituted Benzyl Alcohols . . . . B. Substituted Toluenes . . . . . . C. Substituted Naphthalenes . . . BIBLIOGRAPHY APPENDIX . . . . . . . . . . . . . . . vi Page 85 85 85 86 86 86 87 88 101 Table II. III. IV. .< VII. VIII. IX. XII. XIII. XIV. XV. XVII. XVIII. LIST OF TABLES Infrared data of a- naphthylcarbinyl 3, 5- dinitro- benzoate . . . . . . . . . . . . . . . . . Infrared data of d-naphthylcarbinyl p—nitrobenzoate. Spectral data of the insoluble mixture formed during the solvolysis of 8-methyl-a-naphthylcarbinyl chloride Nuclear magnetic resonance spectral data of some substituted naphthalenes . . . . . . Infrared spectral data of some substituted naphthalenes Comparison of results for Volhard titrations using 50 ml.- and micro- burets . . . . . . . . . . Titration of hydrogen chloride in formic acid by the Volhard method before and after extraction Calculation of end point error in chloride deter-- minations by the Volhard method . . . . Calculation of end point error in chloride deter- mination by the Volhard method . . . . Standardization of silver nitrate by the Volhard method increasing indicator concentration . Titration of chloride by the Volhard method increasing indicator concentration Titration of hydrogen chloride in formic acid by the Volhard method before and after extraction-increased indicator concentration . . . . . . . . . . Precision of potentiometric titration of chloride Accuracy of potentiometric titration of chloride . Titration of chloride after sample extraction Titration of dilute chloride solutions . Titration of dilute chloride solutions . . . . . . . Titration of limiting chloride concentrations to preset potential . . . . . . . . . . . . Page ll 12 19 19 2O 25 26 28 28 29 31 33 35 37 DO hi Table XIX. XXII. XXIII. XXIV. XXV. XXVI. XXVII. XXVIII. XXIX. XXXII. ‘ XXXIII. LIST OF TABLES (Cont.) Dependence of end point potential upon formic acid concentration Rate and equilibrium constants for solvolysis of a-naphthylcarbihyl chloride . . . . . Rate and equilibrium constants for solvolysis of d-naphthylcarbinyl chloride-8-d . . . . . . . Rate and equilibrium constants for solvolysis of d—naphthylcarbinyl chloride-a3a-d2 . . . . . Rate constants for solvolysis of 8-bromo-a-naphthyl- carbinyl chloride and 8-methyl-a-naphthylcarbinyl chloride . . . . . . . . . . . . . . . . . . . . Study of time for appearance of turbidity as a function of initial concentration of a-naphthyl- carbinyl chloride . . . . . . . . . Relative rate ratios of deuterated and substituted a-naphthylcarbinyl chlorides . . . . . . . . . . . Infrared and nuclear magnetic resonance spectral data of fractions from chromatographic studies of the insoluble products from the solvolysis of a-naphthylcarbinyl chloride . . . . . . . . Proton-13C couplings calculated from substituted naphthalenes . . . . . . . . . . . Proton-13C couplings calculated from isomeric toluenes Proton-13C couplings calculated from isomeric benWl alCOhOJ-S O O O O O, O O O O O 0 O O O O O Solvolysis of a-naphthylcarbihyl chloride in 0.32 m water-formic acid. Run 1. . . . .'. . . . . . . SolvoLysis of a-naphthylcarbihyl chloride in 0.32 m water-formic . acid. Run 2. . . . . . . . . . . SolvoLysis of a-naphthylcarbinyl chloride in 0.32m water-formic . . acid. Run 3. . . . . . . . . . Solvolysis of a-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run A. . . . . . . . . . . . . viii Page L2 h6 NB NB A9 58 78 91 92 93 103 103 10b 10h Table XXXIV. XXXV. XXXVI. XXXVII. XXXVIII. XXXIX. XLI. XLII. XLIII. XLIV. XLV. LIST OF TABLES (Cont.) Solvolysis of a-naphthylcarbinyl chloride-8-d in 0.32 m water—formic acid. Run 5. . . . Solvolysis of a-naphthylcarbinyl chloride-8-d in 0.32 m water-formic acid. Run 6. . . Solvolysis of a-naphthylcarbinyl chloride-8-d in 0.32 m water-formic acid. Run 7. . . . . . Solvolysis of a-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run 8. . . . SolvoLysis of a-naphthylcarbinyl chloride-d,d-d2 in 0.32 m water-formic acid. Run 9. . . . . . . Solvolysis of a-naphthylcarbihyl chloride-a,a-d2 in 0.32 m water-formic acid. Run 10. . . . . . Solvolysis of a-naphthylcarbinyl chloride-a,a-d2 in 0.32 m water-formic acid. Run 11. . . . . . . . . Solvolysis of a-naphthylcarbinyl chloride in 0.32 m > water-formic acid. Run 12. . . . . . . . . Solvolysis of a-naphthylcarbihyl chloride in 0.32 m water-formic acid. Run 13. . . . . . SolvoLysis of 8-bromo-d-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run 1h. . . . . Solvolysis of 8-bromo-a-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run 15. . Solvolysis of 8-methy1-a-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run 16. . . ix Page 105 105 106 106 107 ,107 108 108 109 109 110 110 LIST OF FIGURES Figure Page 1. Resonance structures representing hyperconjugative stabilization of the ethyl cation . . . . . . . . . 2 2. Thin layer chromatogram of various factions from chromato- graphic separation of solvolysis products of a-naphthylcarbinyl chloride . . . . . . . . . . . . 15 3. Carbonium ion representing; the transition state for the solvolysis of a-naphthylcarbihyl chloride . . . 60 h. Preferred molecular conformation of a-naphthylcarbinyl chloride . . . . . . . . . . . . . . . . . . . . . 61 5. Carbonium ion representing the transition state for the solvolysis of 8-methyl—a-naphthy1carbinyl chloride. 66 6. Transition states for solvolysis of 8-methyl-a-naphthyl- carbihyl chloride and 8- bromo-a- -naphthy1carbinyl chloride showing participation by the methyl group and the bromine atom . . . . . . . 67 PART I THE EFFECT OF NON-BONDED INTERACTIONS IN SOLVOLYTIC DISPLACEMENT REACTIONS INTRODUCTION About a decade ago, Lewis and Boozer (1) and Shiner (2) reported that deuterium substitution beta to the leaving group in SNl reactions retarded the rate. To explain the results, hyperconjugative stabiliza- tion of the incipient carbonium ion in the transition state was invoked. It was postulated that such stabilization results from a reduction of the C-H and C-D bond vibrational frequencies in the transition state. Since the C-D bond lies deeper in the potential energy well than the C-H bond, the corresponding loss will be less. An equivalent representa- tion is the no-bond structure, illustrated for the ethyl cation in Figure 1. EffectiveLy in the transition state, the C-H bond is loosened more than the C-D bond and kH/kD should be greater than unity. + H H H H I l ' H-C—CH2+ <.—_> H+C=CH2 <—> H-C=CH2 <——> H-C=CH2 I l 1 H H H H+ Figure l. Resonance structures representing hyperconjugative stabilization of the ethyl cation. Secondary deuterium isotope effects are defined to be the effect on rate and equilibrium constants produced by replacement of hydrogen by deuterium in any part of the molecule, providing the bond to the isotopic atom is being neither broken.nx‘formed. In the past decade a considerable amount of data, both experimental and theoretical, has been published (3). Subsequent research on the beta deuterium isotope effect in SNl mechanisms has concerned itself with attempting to prove that hyper- conjugation is the sole or dominant factor. 3 It has been shown that the beta isotope effect is small in 5N2 reactions (b). Shiner (2,5) found that the effect of beta deuteration in SNl re- actions is roughly additive, but that the magnitude of the effect in- creases with increased branching at the beta carbon atom. The solvent and temperature dependence of the isotope effect is rather complicated (3). Usually changes in activation energies and/Or enthalpies and entropies are compensatory. The effect of deuteration in the aromatic side chain has been in- vestigated and found to be complicated (3). The magnitude of the iso- tope effect is strongly solvent and temperature dependent. Large dif- ferences in AAEa are counterbalanced by opposing entropy changes. How- ever, the effect of deuteration of a p-methyl group is less than that of a B-methyl group. The transmission of an isotope effect across a triple bond has been observed by Shiner(6) in the solvolysis of h-chloro-b-methyl-2- pentyne and its deuterated analogs. The kH/kD for Ia is 1-092 and CH3 CD3 I I H 3C-C-CEC-CD3 DscoC-CEC-CHg, I I C1 C1 Ia Ib 1.655 for lb. The isotope effect is considerably reduced by the triple bond. The importance of stereochemistry to hyperconjugation was first suggested by Shiner from solvolysis studies of 2,b,b-trimethyl-2-chloro- pentane and its deuterated analogs (7a). b In comparison to the large reduction in the isotope effect produced by 3,3-dideuterio substitution in 2-chloro-2,b,b-trimethylpentane, the same isotope effect in the series 2-chloro—2-methylbutane, 2-chloro—2- methylpentane was large and approximately constant (7b). It was suggested that maximum hyperconjugative.stabilization of the incipient carbonium ion would be attained only when the C-H bond was parallel to the developing n orbital. This hypothesis has been tested by Shiner and co-workers. They found that the solvolysis rate retarda- tions caused by substitution of l, 2, and 3 deuterium atoms in one methyl group of t-butyl chloride were not quite cumulative but increased as the extent of deuteration increased (8). These differences were quantitatively treated assuming confOrmation dependence. Further sup- port was obtained from solvolysis studies of compounds IIa, IIb, and IIc(9). 'IIa. IIb IIc kH/kD = 1.1A kH/kD = 0.986 The observed rate ratios are as expected, since in IIb the C-D bond is almost parallel to the vacant n orbital developing in the transition state, whereas in IIc the C-D bond is almost perpendicular. The small rate retardation in IIc is attributed to the inductive effect. 7 The most striking effect was Observed in the rates of solvolysis of cis-h-tfbutylcyclohexyl broSylate-trans-2-d and cisehjt-butylcy61o— hexyl brosylate-cis-2-d (10). The axial B—deuterium (-trans-2-d) 5 exhibits a rate retardation of l.h36, whereas the equatorial B-deuterium (-cis-2-d) slows the rate by only 1.096. Hyperconjugation in both ground and transition states has become an area of profound disagreement (11). An alternate explanation for ground state effects in terms of hybridization has been advanced (12). The origin of the Baker-Nathan effect has been the subject of much dis- cussion (3,12). The claim that the existence of beta deuterium isotope effects is evidence for hyperconjugation has been criticized by Dewar (l2). Hybridization has been invoked to explain the alpha deuterium isotope effect (13). Bartell has proposed a theory of non-bonded interactions. The theory was first applied to molecular phenomena and then extended to secondary deuterium isotope effects (lb). Bartell has suggested an approximate equality of non-bonded interactions for atoms bonded to the same carbon (lha). This approximate equality of C'-C, Co-H, and H--H non-bonded interactions no longer applies for atoms bonded to adjacent carbon atoms. On this basis he was able to account for the regular de- crease in the C-C bond length as the number of adjacent atoms is de— creased (lha, lbb). This model also accounts for the small changes in C-H bond lengths as the hybridization is changed from Sp3 to sp2 to Sp (lba, lhb). Using non—bonded potential functions, Bartell was able to successfully calculate the strain energy in cyclobutane (lha). The extension of the theory to secondary isotope effects is based on the principle that the amplitudes of vibration of hydrogen atoms are larger than the amplitudes of the heavier deuterium atoms by a pre- dictable amount. Therefore, non-bonded repulsions, averaged over the 6 atomic vibrations, are greater for hydrogen atoms than for deuterium atoms. Moreover, there are more and stronger non-bonded repulsions in the crowded tetrahedral reactant than in the trigonal carbOnium ion. Thus the relief of non-bonded repulsions at the transition state is greater for the protio compound than for the deuterio compound. The effect of deuterium substitution on the activation energy of t—butyl chloride is calculated to be 22 cal./D (lbd). Bartell has calculated the effect of deuterium substitution on the gas phase equilibrium (lhd). MesB:NMe3 = MesB + :NMes The experimentally observed value of AAEa is 22 cal./D. The best calcu- lated value is 20 cal./D but the result is sensitive to the model as- sumed for the complex. Bartell concludes (1bb): that numerical computations Show the effect is entirely reasonable in magnitude, but the numerical values depend so strongly upon assumed bond angles and lengths (which are at present largely conjectural) that a definite conclusion cannot yet be made. The best estimate suggests that some hyperconjugative delocalization occurs but that this has the effect, in turn, of enhancing the non-bonded effect. In the SNl reactions so far reported, it has been impossible to separate effects due to hyperconjugation and non—bonded interactions or to decide on the relative magnitudes of each. Therefore to assess the role of non-bonded interactions in solvolytic displacement reactions, it is necessary to find a system in which the possibility for hyper- conjugation has been eliminated. The following naphthalene derivatives offered themselves as attractive possibilities. x CD2C1 x = H, D, CH3, CD3, Br For these compounds it is impossible for groups in the 8 position to resonately stabilize the incipient carbonium ion in the transition state. Thus rate differences between the protio and correSponding deuterio compounds would only be due to non-bonded interactions. There- fore, the study of the solvolysis of these compounds was undertaken. During the course of these investigations several instances of "steric" isotope effects have been reported. Melander and Carter (15) obtained a kD/kH value of 1.19 from studies of the rates of racemiza- tion of 2,2'-dibromo-h,h'-dicarboxybipheny1 and its 6,6’-dideuterio derivative at -19.8°.. Mislow and co-workers (16) studied the effects of deuterium substitution on the rate of racemization of 9,10-dihydro- b,5-dimethy1 phenanthrene. CD3 D3 va Vb Vc / = = / = k k 1.05 kD/kH 1.13 kD,kH 1.18 The effect in Vc is additive. The authors conclude that the 5% effect in Va may be either a "steric" isotope effect or a result of a change in the potential energy barrier to torsion around the 9,10-bond. They conclude that the 13% effect observed in Vb and Vc is steric in origin. 8 Raaen and co-workers (17) report a steric isotope effect for the formation at 0° of 2,h-dinitrophehylhydrazones. The deuterium contain~ ing ketones whose isotope effects were determined with respect to the undeuterated species are shown in structures VI-IX along with the cor- responding kH/kD values. CH3 1 PhCOCD3 Phco-c-CD3 PhCOCDZCH3 PhCOCHZCD3 I CD3 1.119 t 0.005 . 1 10A : 0.002 1.0A6 1.12A 0.9952 VI VII VIII IX The authors feel that these observations are explicable only on the basis of steric effects and are in agreement with the mechanism proposed for 2,h-dinitrophenylhydrazone formation. Examination of Fisher-Herschfelder models reveals that 8-methy1— and 8-bromo-a-naphthylcarbinyl chlorides are severely strained. The existence of strain in some naphthalene compounds has been demonstrated by X-ray diffraction (18). Octamethylnaphthalene (19) has been shown to be severely distorted. A completely planar molecule would require the a-methyl groups to be 2.h A apart, a distance well below the sum of the appropriate van der Waals' radii. As a result, the a-methyl groups are bent out of the plane by about 28°. The B-methyl groups are dis- placed in the opposite directions by a smaller amount. This is probably a consequence of a slightly sideways displacement (0.06 A) of the a- methyl groups . Therefore it was felt that a comparison of the rates of the 8-methyl- and 8-bromo-a-naphthylcarbinyl chlorides with a—naphthylcarbinyl chloride might yield additional insight into the effects of ground state steric strains on solvolysis reactions. 9 Steric strain acceleration in solvolysis reactions of alkyl halides, due to relief of ground state non-bonded repulsions in the trigonal transition state, is not a new concept (20). For example, Brown and Moritani (23£)claim.that the observed relative solvolysis rates of the series MeCMeZC1, EtCMeZCl, iPrCMeZCl, tBuCMezCl, tAmCMeZCl, of 1.0, 1.67, 0.88, 1.21, and 5.67 can only be explained on this basis. How- ever, it should be mentioned that such an explanation has been ques- tioned (21). The existence Of steric acceleration in solvolysis reactions has been convincingly demonstrated by Moritani and co-workers (22) from their studies of the acetolysis of trans-l- and 2-decalyl p—toluene- sulfonates. The observed rate sequence was 1 equatorial < 2 equatorial < 3 axial << 2 axial. The relative rates were 0.5, 1.0, 3.1, and 27.6. Similar results were obtained by Nishida (23) from a study of the acetolysis rates of the isomeric p—toluene sulfonates of chlolestan-2a, 2B, 30, 3B, and 60-01. The observed sequence of rates was 3B’E'6a < 20 <.3a << 25. The relative rate sequence was 1.0, 0.9, 3.1, 6.1, and 31. Winstein and Holness (2h) ascribed the rate increase factor of 3.58 observed in the formolysis of cis-hrtfbutyfilcyclohexyl pftoluene- sulfonate over the corresponding trans isomer to steric acceleration. Brown and cO-workers (25) have found conformation of these steric effects from the rough correlation observed between the rates of ketone reduction with sodium borohydride and the rates of solvolysis of the corresponding alkyl halides and aryl sulfonates. It was observed that a rough linear free energy relationship existed between the rate of re- duction of five to ten membered cycloalkanones with sodium borohydride and the acetolysis of cyclic tosylates (25a,c). RESULTS AND DISCUSSION I. Synthesis A. d-Naphthylcarbinol. a—Naphthylcarbinol and its various deuter- ated analogs were prepared from the appropriate lenaphthoic acids by re- duction with lithium aluminum hydride or deuteride. The identity of the compounds was established by infrared and nuclear magnetic resonance Spectra. B. 8-Methy1-d—Naphthylcarbinol. 8-Methy1-a-naphthy1carbinol was prepared by reduction of 8—methyl-1—naphthoic acid with lithium aluminum hydride (26). C. 8-Bromo-a-Naphthylcarbin01. 8-Bramra-naphthylcarbin01 was pre- pared by 1ithidm aluminum hydride reduction of 8-bromo-lvnaphthoyl chlor- ide (26). D. a-Naphthylcarbinyl,pgTOluenesulfonate. The tosylate ester of a-naphthylcarbinol was synthesized from the corresponding sodium salt of the alcohol and.p-toluenesulfonyl chloride. It decomposes at 55.50. It decomposes rapidly in the crystalline state under dry nitrogen or argon. The ester appears to be stable in anhydrous ether, but readily decomposes on recrystallization in solvents other than pentane. Similar instability was noted for the tosylate of B-naphthylcarbinol by Jacobs and Singer (27). They observed decomposition of the crystalline com- pound to a green tar at 61.50. The tosylate esters, therefore, were considered unsuitable for kinetic study. 10 11 E. a-Naphthylcarbihyl 3,5-Dinitrobenzoate. Attempted preparation of a-naphthylcarbinyl 3,5-dinitrobenzoate from sodium a-naphthylmethylate and 3,5-dinitrobenzoyl chloride gave an amorphous yellow material that was insoluble in common organic solvents. The infrared spectrum indicated that it was a mixture. The material softened and coalesced at 150-1600 turning to a viscous oil at 190°. d-Naphthylcarbinyl 3,5-dinitrobenzoate was prepared by dissolving d-naphthylcarbinol and 3,5-dinitrobenzdyl chloride in “ether containing pyridine. The infrared spectrum was consistent with the prOposed struc- ture and the principal absorptions are given in Table I. Table I. Infrared data of a-naphthylcarbinyl 3,5-dinitrobenzoatea Group Absorption (microns) C=0 5.80, 7.85, 8.55 “N02 ’ 6.5, 7.115 aromatic 3.25, 6.15, 6.28 aliphatic 3-5 aKBr pellet. F. a-Naphthylcarbinyl pritrobenzoate. The ester was prepared from a-naphthylcarbinol and p-nitrobenzoyl chloride in ether contain- ing pyridine. The infrared data were consistent with its.structure. Principal absorptions are given in Table II. 12 Table II. Infrared data of O'Daphthylcarbinyl p-nitrobenzoatea Group Absorption (microns) C=0 5.80, 7.90, 8.55 N02 6.55, 7.115 aromatic 3.25, 6.15, 6.25 aliphatic 3-5 aKBr pellet. G. Arylcarbigyl Chlorides. The arylcarbinyl chlorides.were synthesized from the appropriate alcohol and thionyl chloride. Each arylcarbinyl chloride was prepared immediately before a series of kinetic runs and stored under dry petroleum ether at approximately 0°. Before a kinetic run an appropriate amount of compound was removed, placed in a weighing bottle, and gently ground with a spatula until a fine powder was obtained. The bottle and its contents were then placed in a desiccator and kept under high vacuum for 10 to 12 hours to remove all solvent. The nuclear magnetic resonance and infrared Spectra of the chlor- ides were in accord with their structures. II. Product Studies A. Methanolysis of a-NaphthylcarbinylAp:Nitrobenzoate and a- Naphthylcarbinyl 3,5-Dinitrobenzoates The methanolysis.of these esters was studied to ascertain whether they would be suitable derivatives for kinetic studies. Thus it was essential that during methanolysis they suffer alkyl oxygen rather than acyl oxygen fission. 13 d-Naphthylcarbinyl 3,5-dinitrobenzoate was unsuitable because of its limited solubility in anhydrous methanol. Chromatographic studies showed only the formation of d-naphthylcarbinol. Chromatographic analysis of the mixture from the methanolysis of a-naphthylcarbinyl p—nitrobenzoate yielded only a-naphthylcarbinol and methyl p—nitrobenzoate as established by infrared and m.p. These results and the failure to detect any a-naphthylcarbinyl methyl ether indicate that these esters undergo only acyl oxygen fis- "sion during methanolysis. Therefore no further conSideration was given to these derivatives. B. Insoluble Products Formed During Solvolysis of a-Naphthyl- carbinyl Chloride. Due to the complex nature of the insoluble products formed during the solvolysis of a-naphthylcarbinyl chloride, only pre- liminary results are reported. In order to approximate kinetic conditions, a 0.01h M solution of a-naphthylcarbinyl chloride in 97% formic acid was prepared. After 3.5 days the precipitated material was collected, dissolved in ether, and the formic acid removed. The nuclear magnetic resonance spectrum of the product mixture exhibits two principal absorptions: one, a broad series of unresolved peaks characteristic of aromatic protons centered around 7' = 2.5; and second, broad peaks at 1' = 5.2, h.h. The peaks at 1' = 5.2, h.h are characteristic of the methylene protons of arylcarbinyl derivatives, 1.3., methylene protons of d-naphthylcarbinyl chloride, d-naphthylcarbinol, and benzyl formate appear at 7' - 5.15, 'T = 5.13, and. T'- h.8 respec- tively. 1b The infrared Spectrum exhibits, in addition to aromatic and ali- phatic bonds, a carbonyl absorption at 1720 cm.-1. The spectrum reveals the absence of a hydroxyl group. FUrthermore it is impossible to verify the presence of chemically bound chlorine. A positive silver nitrate test indicated the presence of chemically bound chlorine in the mixture. This was further substantiated by the infrared spectrum of the recovered material which exhibited a weak band at 3500 cm.-1. The mixture was chromatographed on Silica gel. Thin layer chroma- tography was then utilized to determine the extent of separation and the number of products. Figure 2 is a reproduction of the thin layer chromatogram. It suggests that the mixture contains at least 5 differ- ent products. This may well be a minimum as spots 20 and 21 do not Show much movement and the small amount of material eluted by methanol was nOt spotted. Those fractions which had approximately the same rf values were combined before infrared and nuclear magnetic resonance Spectra were taken. The salient features of the spectral data are: The spectrum of each fraction bears no simple relationship to those of the pure chloride or alcohol; all fractions except No. 1-9 exhibit a carbohyl absorption at 1720 cm.'1 in the infrared; after fraction 12 a band at 1690 cm."1 appears; the infrared data reveal no evidence which would indicate the presence of a hydroxyl group; the nuclear magnetic resonance spectra of every fraction have peaks characteristic of protons of an aromatic methylene group containing a functional entity but no absorption characteristic of aromatic methyl protons; and absorptions in the aromatic regions are broad and apparently unresolved. 15 Solvent Front f \‘ i". z"! a I": 1'”? (1': 13./11.1. ..: la ~ ' ~’ c.J "\ ’1 . : : 1 5 I 1 I‘ a l‘ I . 4’ s-) K’] I“ r ' H I, ‘I I", '73 ”‘s “I \_l I J I I " .I - ,1: b ’ ‘1 I f‘ ' ‘ \ l l I ‘J L) '._,' (“I {31 ‘\I \I I \ II \ I I \[ SQOttli‘lg Line - 1 , 1"\ 1.1T \vi 1 l J, l J l l l l- l l 1 I l 1 l'Ll 5 6 7 8 9 '10 ll 12 111 .15. 16 19 20 21 Fractions -- Solvent 1:1 CCl4-C5H5 Figure 2. Thin layer chromatogram of various fractions from chromato- graphic separation of solvolysis products of a-naphthyl- carbinyl chloride. Fractions and 'e‘luting solvents: 1-5, cm ° 6 7 5:1 CCl4—C6H - 8 9 1:1 CCl -C H6: 10-111 1: CCl - c6112} 15-18 051153 l9-2i’1:ic.H.-Et28; 32,23 EtZO; 2 CH, H. 16 From these limited facts the following tentative conclusions are drawn concerning the nature of these insoluble products. The first fraction (No. 1-9, Figure 2) may be multi-substituted arylcarbinyl chlorides of the following type: I / 2C1 n2: 1 The nuclear magnetic resonance Spectrum of this fraction shows two peaks of unequal intensity at 'r = 5.2 and 'T'= 5.1, possibly ascribable to magnetically non-equivalent methylene protons. FUrthermore, the infrared Spectrum.exhibits an unusually strong band at 12b5 cm..'1 with a Shoulder at 1280 cm.'l, similar to the bands in the spectrum of a-naphthylcarbinyl chloride. These absorptions, due to usually weak carbon hydrogen de- formations, may be strongly enhanced by the presence of electronegative elements (28). The major amount of the material appeared to be contained in frac- tions 10 and 11 of Figure 2. The infrared shows, in addition to the usual aromatic and aliphatic absorptions, bands at 1720 cm."1 and 1160 cm.-1. The nuclear magnetic resonance spectrum shows peaks at 7' a 5.3, h.5, and a broad aromatic absorption centered around 1' = 2.5. Benzyl formate has a carbonyl absorption at 1720 cm.’1 in the infrared. Its nuclear magnetic resonance Spectrum exhibits a peak at 1' = h.8 for the methylene protons, with the formyl proton appearing at 1' = 1.9. From these results, it is suggested that this material is a formate ester. 17 The remaining products appear to be of higher molecular weight. They all appear to exhibit the same general Spectral features as pre- viously noted with one important exception. The infrared spectra of fractions above 13 in Figure 2 Show a band at 1690 cm.'1. This band ap- pears to grow in intensity relative to the band at 1720 cm.'1. In the original mixture it appears as a very small peak at the base of the 1720 cm."1 band. Considering the limited amount of data, it appears impossible to suggest what structural unit this absorption represents. The spectral data indicate that the principal remaining products are formate esters. The following general structure is suggested: 0 I! CH 2-O-c—H n n.) 0 The formation of these products is visualized as an electrophilic attack of the carbonium ion formed during the solvolysis of a~naphthyl- carbinyl chloride on either the arylcarbinyl chloride, arylcarbinol, or arylcarbinyl formate. C. Insoluble Products FOrmed During Solvolysis of 8-Methyl-a- Naphthylcarbinyl Chloride. The precipitate obtained from.solubility studies of 8-methyloa-naphthylcarbinyl chloride was dissolved in ether and washed free of formic acid. The presence of at least five components in the mixture was indi- cated by thin layer chromatography. Since some of the material showed 18 only Slight movement for the eluting solvents pentane, carbon disulfide, and benzene, the actual number of components in the mixture may be larger. The principal infrared and nuclear magnetic resonance absorption peaks of the mixture are listed in Table III. Tables IV and V contain respectively infrared and nuclear magnetic resonance absorption peaks of some naphthalene derivatives. Comparison of the nuclear magnetic resonance data in Tables III and IV suggests that the mixture contains peaks characteristic of magnetically nongequivalent aromatic methyl protons, protons of magnetically non-equivalent methylene carbons con- taining a functional group, and peaks characteristic of aromatic pro- tons. Due to the range over which these absorption peaks occur, the aromatic region appears anomalous. The peaks in this region can be divided into three main groups: the largest concentration of protons appears to be centered at 1" - 2.52, a broad peak characteristic of formyl protons occurs at 7r = 1.97, and a series of peaks is centered at T = 3.17. The infrared data of Table III do not suggest the presence of a hydroxyl group. The band at 1720 cm.-1 is ascribed to the carbonyl of a formate ester. The appearance of a band at 1250 cm.-1, its presence in the parent chloride, and its absence in the parent alcohol suggests, as in the previous section, the presence of a chloromethylene group. From these data and the results of the previous section, it is suggested that the mixture contains multi-substituted arylcarbinyl chlorides and formates. Interestingly, on the basis of the nuelear magnetic resonance data, the following reaction producing acenaphthene does not appear to occur. 19 Table III. Spectral data of the insoluble mixture formed during the solvolysis of 8-methyl-d-naphthylcarbinyl chloride I.R. Absorptions (cm.'1) N.M.R. Absorptions (1') 2mm 73? 1916 7.33 1852 7.17 1720 7.00 1595 5.03 1850 8.92 1250 A.9O 1156 h.3O 1097 3.5 - 1.67 10A2 Table IV. Nuclear magnetic resonance spectral data of some substituted naphthalenes. Compound CH3 AbSOCH:ion (fi-Aromatic 8-Methyl-a-naphthylcarbinyl chloride 7.00 b.95 2.17-2.83 l-Bromo-8-methyl naphthalene 6.92 2.20-3.08 a-Methy lnaphthalene 7.75 2.33-3.25 Acenaphthene 6.8 2.33—3.08 8-Methyl-d-naphthylcarbinol 7.15 5.10 2.25-3.00 2O CH3 CHZCl CH3 CH2 CH2 --—CH2 Table V. Infrared spectral data of some substituted naphthalenes. Compound Absorptions (cm.-1) 8-Methyl-d-naphthylcarbinol 3600, 3000, 1920-1600, 1510, 1&60, 1390, 1170, 1000 8-Methyl-o-naphthylcarbinyl 3000, 1920—1600, 1510, 1h80, 1h60, chloride 1390, 1250 III. Analytical Methods for the Determination of Chloride A. Volumetric Determination of Chloride by the Volhard Method. The experimental procedures were adapted from Blaedel and Meloche (29), Koltoff and Sandell (30), and Swift (31). The reproducibility of rate constants is sensitive to the accuracy and precision of the analytical method used to follow the appearance of one of the products in a reaction. Fainberg and Uinstein (32) report rate constants to 1% using this analytical method, but give no details of the accuracy of the Volhard method when titrating samples containing less than 0.2 meq. of chloride. Numerous other authors have used this analytical method, but details of its accuracy are rather scarce. There— :fore, the following experimental work was performed to determine both the accuracy and precision for samples containing chloride concentra- tions similar to those which were expected during kinetic runs, i.e ‘3 0.1 to 1 meq. 21 Silver nitrate solutions were standardized against primary standard sodium chloride solutions. Potassium thiocyanate solutions were titrated against the silver nitrate solutions. Micro—burets (10 and 5 m1.) calibrated in 0.02 and 0.01 ml. intervals respectively were used. Samples containing 2.5 to 5 meq. of chloride were analyzed to within the 0.1% level. Table VI lists the results obtained from the standardization of silver nitrate against 0.1011 M sodium chloride using both the micro- and 50 ml. burets. The percentage difference is only 0.089% and a high level of precision is indicated. Table VI. Comparison of results for Volhard titrations using 50 m1.- and micro-burets. AgNO3 KSCN A N03 NaCl AgNO3 Avg. Buret m1. ml. CN m1. _ Ratio % Dev. 50 ml. 35.09 38.88 0.9025 50 ml. 35.00 38.80 0.9021 0.9023 50 ml. 36.00 39.90 0.9023 50 ml. 28.11 1.82a 25.00b 0.1125 0.000 50 ml. 23.70 1.35a 25.00b 0.1128 -0.089 a b 0.1125 50 m1. 23.00 0.62 25.00 0.1126 0.089 50 ml. 22.99 0.59"71 25.00b 0.1125 0.000 Micro- 9.160 0.212 0.9023 10.00b 0.1127 0.098 Micro- 9.125 0.155 0.9023 10.00b 0.1125 0.1126 -0.089 Micro- 9.165 0.219 0.9023 10.00b 0.1127 0.089 a . 10 ml. buret used. b 0.1011 M NaCl solution. Volhard procedure 1 used Volhard procedure 2 used for 50 ml. burets. for micro-buret. 22 Since samples were to be quenched during kinetic runs by extract- ing the aliquot of the reaction mixture with carbon tetrachloride, it was imperative to know the resulting chloride loss. Fainberg and Win- stein (32) and Bateman and Hughes (33) indicate that at least 99.8% of chloride is recovered after extraction. This problem was reinvestigated. Table VII lists the results obtained for samples containing 31 to 38 meq. of chloride. For these data 2 ml. of 0.33 M ferric nitrate indicator was used. Before analyzing these results, a discussion of the sources and magnitudes of possible error in the titration of solutions less than 10_2 M in chloride is necessary. A serious source of error at these concentrations is the appearance of a false end point early in a titra- tion (29). This is caused by the reversible formation of the colored (FeSCN)+2 complex before the number of meq. of added Ufiocyanate equal to the excess meq. of silver ion has been added. This false end-point which faded upon stirring for about one minute introduced an error of approximately 1%. At these concentrations another problem was the non-abrupt color change of the indicator in the region of the end point. Using 2 ml. of 0.33 M indicator, the color of the solution changed from essenti- ally clear to intense orange over an interval of about 0.1 m1. of thiocyanate. Therefore, titration to a constant color change was found to be very difficult and in some instances many titrations had to be performed and discarded. The resulting color change was reproducible to about 0.01 ml. of thiocyanate resulting in deviations of about i 0.3%. This problem introduced two other possible sources of error: one the reproducibility to the same color change over an extended period 9 23 Table VII. Titration of hydrogen Chloride in formic acid by the Volhard method before and after extraction8 s 1 . b §OP U.E. E.C Mg. C1, Avg. A B C 1 - 31.26 0.192 1 - 31.15 31.20 -0.160 1 - 31.18 -0.06A 1 — 31.22 0.06A 0 00° 0.06A l - 31.19 31.20 -0.032 -0.032 1 - 31.19 -0.032 40.032 2 — 27.93 0.036 2 - 27.91 27'92 0.036 O 072 2 — 27.98 0.1A3 ' 0.215 2 - 27.96 27.9A 0.072 0.1A3 2 — 27.88 -0.215 -O.1A3 3 - 2A.A8 0.000 3 — 2A.A7 28‘88 -0.0A1 -0 531 3 - 2A.35 2A 35 0.000 ° -0.531 3 - 2A.35 ' 0.000 -0.531 A - 21.05 -0.0A8 A - 21.09 21.06 0.1A2 A — 21.05 -0.0A8 A - 20.98 0 1A3 '0'522 -0.380 A - 21.00 20.95 0.239 -0.285 A - 20.88 -O.33A -0.855 stock - 37.91 0.026 stock - 37.89 37'90 -0.026 ‘0'106 stock - 37.86 37.86 0.000 —0.106 aVolhard procedure 2, 10 ml. aliquots. bU.E. is unextracted sample. CE. is extracted Sample. A = % deviation of each sample in a group from average of that group. B = % deviation of average of E. samples from U.E. average. C = % deviation of each E. sample in a group from average value of U.E. for each group. 2A of time; and two, the non—equivalence of the observed end point with the equivalence point. Over a two day period the molarity of a silver nitrate solution decreased by 0.007 which seems excessive considering the caution exercised in handling the silver nitrate solutions. Swift (31) has calculated the amount of indicator necessary to produce simul— taneous occurrence of the end point and the equivalence point when titrating under equilibrium conditions. In the present method the silver chloride was removed by shaking it with nitrobenzene, 3.3,, non- equilibrium condition. Therefore, the problem of calculating the end point error is reduced to a calculation of the excess thiocyanate ion ' concentration over Silver ion concentration at the end point as a func- tion of indicator concentration. Implicit is the assumption that the precipitated silver chloride is no longer in equilibrium with the solu- tion. The validity of this assumption was demonstrated by the stabil- ity of the color change over long periods of time. Using the equations as outlined by Blaedel and Meloche (29) it can be Shown that the end point is past the equivalence point by a volume of 0.1 M potassium thio- cyanate equal to 0.009 ml. of 0.1 M potassium thiocyanate using 5 ml. of 0.33 M ferric nitrate indicator and approximately 100 ml. total titrat- ing volume. For macrOSCOpic samples the error so introduced is less than 0.1%. Using these equations, various concentrations of 0.33 M indicator, and various total titration volumes, the approximate error has been calculated. The results are given in Table VIII. The errors are calculated for varying amounts of chloride requiring different ‘volumes of a given silver nitrate concentration. In these calculations, thm:ratio of silver nitrate to potassium thiocyanate was assumed to be Llrutyu The results are valid because experimentally the ratio deviated 25 insignificantly from unity. The calculations reveal that for a given molarity of silver nitrate and a given indicator concentration, a de- crease in the required volume of silver nitrate leads, as expected, to an increase in the error. The error grows considerably as both the molarity and the required volume of silver nitrate decrease. Increas- ing the amount of indicator reduces the error. The error ranges from approximately 0.1 to 1% for 5 ml. of indicator and from approximately 0.2 to 2% for 2 m1. Swift suggests using 2 M indicator. Table IX sys- tematically lists the calculated error in the required volumes of silver nitrate for indicator concentrations of 2 and A m1. These calc- ulations indicate that better accuracy would be obtained by using the higher indicator concentration and by reducing the total titrating volume. Furthermore, the calculations indicate that chloride concen- trations down to 0.1 meq. should be analyzable to within 1%. Table VIII. Calculation of end point error in chloride determinations by the Volhard method. Tit. M Ml. M M1.a M M1. Vol. Fe(N03)3 Fe(N03)3 KSCN KSCN AgN03 AgN03 ' %Errorb 100-110 0.33 2 0.1. 0.015 0.1- 10.000 0.15-.165 100-110 0.33 2 0.1 0.015 0.1 5.000 0.30-.33 100-110 0.33 2 0.05 0.031- 0.05 10.000 0.31 100-110 0.33 2 0.05 0.031 0.05 5.000 0.62 100-110 0.33 2 0.05 0.031 0.05 2.000 1.55 100-110 0.33 5 0.1 0 009 0.1 10.000 0.09-.1 100-110 0.33 5 0.1 0 009 0.1 5.000 0.18- 2 100 0.33 5 0.05 0.018 0.05 10.000 0.18 100 0.33 5 0.05 0 018 0.05 5 000 0.36 100 0.33 S 0.05 0.018 0.05 2 000 0.90 , aCalculated excess at end point. b% Error is the error in vol. of AgN03 assuming AgNOs/XSCN ratio - l. 26 Table IX. Calculation of end point error in chloride determination by the Volhard method Tit, M1. M M Ml. M Ml. V01. Fe(N03)3 Fe(N03)3 KS'CN KSCN ‘ AgNOg, AgN03 % Errora 70 2 2 0.1 0.00A 0.1 10.000 0.011 70 2 2 0.1 0.00A 0.1 5.000 0.08 . 100 2 2 0.1 0.007 0.1 10.000 0.07 100 2 2 0.1 0.007 0.1 5.000 0.1A 70 2 2 0.05 0.008 0.05 10.000 0.08 70 2 2 0.05 0.008 0.05 5.000 0.16 70 2 2 0.05 0.008 0.05 2.000 0A 100 2 2 0.05 0.013 0.05 10.000 0.13 100 2 2 0.05 0.013 0.05 5.000 0.26 100 2 2 0.05 0.013 0.05 2.000 0.65 13 70 A 2 0.1 0.003 0.1 10.000 0.03 70 A 2 0.1 0.003 0.1 5.000 0.06 100 A 2 0.1 0.005 0.1 10.000 0.05 100 A 2 0.1 0.005 0.1 5.000 0.1 70 A 2 0.05 0.006 0.05 10.000 0.06 70 A 2 0.05 0.006 0.05 5.000 0.12 70 A 2 0.05 0.006 0.05 2.000 0.3 100 A 2 0. 05 0.010 0.05 10.000 0.1 100 A 2 0.05 0.010 0.05 5.000 0.2 100 A 2 0.05 0.010 0.05 3.000 0.5 a% error is the error in vol. of AgN03 assuming AgN03/RSCN ratio = 1. 27 Tables X and XI give the results obtained from titrating known amounts of chloride using 2 ml. of 2 M indicator. From the data in Tables IX, X, and XI it is apparent that the observed error agrees, within the accuracy of the calculations, with the expected error. Comparison of the results from Tables IX, X, and XI with the results of Table VII reveals a significant improvement in the accuracy using the increased indicator concentrations and decreased titrating volumes. Furthermore, a sharper and more reproducible color change was obtained. Finally, from Table X the ratio of Silver nitrate to potassium thio- cyanate is slightly greater than unity, whereas using less indicator the ratio was slightly less than unity. The results are in agreement with theory. Table XII lists data obtained from the titration of extracted and unextracted samples of 0.05 and 0.0A M hydrogen chloride in formic acid. An exact analysis of the loss of chloride during extraction is difficult in view of the previous discussion. Solutions 3 and A of Table VII Show large percentage deviations of the average values of the extracted samples from the unextracted. The data in Tables VII and XII, which Show positive values for this percentage, indicate that the average loss of chloride is less than the reproducibility of the analytical method. Percentage deviations within a group from their average further support this conclusion. If for the previous reasons the results of Table XII are more significant than those in Table VII, a reasonable level of precision is i 0.15% with an average apparent loss of chloride of - 0.12%. Thus it is concluded that the average loss of chloride during extraction is of the same order of magnitude as the precision of the analytical method. 28 Table X. Standardization of Silver nitrate by the Volhard method increasing indicator concentrationa E @321 Ml. AgNO3 Ml. KSCN §§§§3 Ml. NaCl % fig§03 % Dev. — A.000 3.980 1.005 - - b.000 3.975 1.006 - - A.500 A.A70 1.007 - - 5.000 A.970 1 006 - 5.069 9.900 0.102 1.006 10.00 5.173 -0.019 9.9A0 0.1A0 1.006 10.00 5.172 —0.038 9.980 0.190 1.006 10.00 5.178 0.077 Av. 5.17A aVolhard procedure 3. Table XI. Titration of chloride by the Volhard method increasing indicator concentrationa M NaCl Mg. Cl Mg. Cl % Dev. E 102 taken found AVQ' % Error from avg. 5.11h 18.13 18.11 -O.llO 0.000 18.13 18.11 18.11 -O.llO 0.000 18.13 18.11 -O.llO 0.000 5.166 18.32 18.31 -0.055 0.055 18.32 18.29 18.30 -O.léh. -0.055 18.32 18.30 -O.lO9 0.000 aVolhard procedure 3. 29 Table XII. Titration of hydrogen chloride in formic acid by the Volhard method before and after extraction - increased indicator concentration Soln. No. U.E.b B.C Mg. Cl Avg. A B C S - 17.25 0.000 5 — 17.25 17.25 0.000 5 - 17.25 0.000 -o.17h 5 - 17.22 0.000 -o.17h 5 - 17.22 17.22 0.000 -o.17u 5 - 17.22 0.000 -o.17b 6 - 13.85 -o.lhh 6 — 13.88 13.87 0.072 6 - 13.89 o.1hh 0.072 6 - 13.87 -o.072 0.000 6 - 13.88 13.88 0.000 0.072 6 - 13.88 0.000 o 072 aVolhard procedure 3, 10 ml. aliquots. bU.E. is unextracted sample. CE. is extracted sample. A = % deviation of each sample from average. B = % deviation of average of E. samples from U.E. average. C = % deviation of each E. sample in a group from average value of U.E. for each group. B. Determination of Chloride by Potentiometric Titration. Due to the difficulties and limitations found with the Volhard method, a more accurate method for titrating chloride was needed. Shiner (38) has reported that in acetic acid - sodium acetate buffer, chloride concen— trations greater than 0.1 meq. can be accurately determined by potentio- metric titration. 30 Experiments were performed to ascertain the limitations of the pro- cedure in aqueous formic acid and to reinvestigate the loss of chloride during extraction. Volumetric glassware except the micro-burets was calibrated. The precision of the calibrations was within 0.1%. The corrected volumes of the 1 l. volumetric flasks were negligible and thus usually neglected. It was found necessary to perform the experimental work in an air condi- tioned room maintained at approximately 23 i 2°. For solutions greater than 10’3 M in chloride end points were ob- tained by two methods: the derivative technique and graphical analysis (35,36). The end point using the derivative technique was taken as the mid- point of that increment of titrant at which the rate of potential change was greatest, 1.3., AE/AC was a maximum. In a titration the increments of titrant added near the equivalence point were adjusted so as not to give a disproportionate weight to the normal error in measurement. Graphical analysis consisted of plotting ml. of titrant against the corresponding potentials. The end point was taken as the midpoint of the straight line segment of the titration curve. This method, which is inconvenient to use, was employed primarily to obtain the end point potential and to verify the results of the previous method. Table XIII reveals the precision obtained by potentiometric titra- tion. 0f the twenty determinations only four show deviations from their predicted end points, and of the four only two (numbers 15 and 16) appear to deviate significantly. This conclusion is supported by the end points obtained by the graphical method. Omitting the four question- able samples the derivative end point is 7.735 i 0.015 ml. Including 31 Table XIII. Precision of potentiometric titration of chloridea 8:25;: A c Emf g AgN03b 1 7.78 7.78 7.735 270.5 0.02611 2 7.72 7.78 7.780 269.0 0.02617 3 7.78 7.78 7.780 263.0 0.02611 10 7.78 7.78 7.730 268.5 0.02611 11 7.78 7.78 7.780 268.0 0.02611 12 7.78 7.78 7.780 265.5 0.02611 8 7.72 7.72 7.735 263.0 0.02617 5 7.76 7.72 7.735 259.5 C802608 6 7.72 7.72 7 730 263.0 0.02617 7 7.72 7.72 7.725 268.3 0.02617 8 7.72 7.72 7.720 268.5 0.02617 9 7.72 7.72 7.730 265.8 0.02617 20 7.72 7.72 7.735 263.5 0.02617 13 7.75 7.75 7.727 268.2 CL02607 18 7.75 7.75 7.737 262.5 0.02607 15 7.71 7.75 7.737 268.5 0.02621 16 7.77 7.75 7.772 266.8 0.02600 17 7.73 7.73 7.720 262.5 0.02618 18 7.73 7.73 7.730 262.3 0.02618 19 7.73 7.73 7.730 262.0 0.02618 a! NaCl = 0.08052; 5 cc. of HCOOH; pipet volume (pip. vol.) = 8.986 ml. M calculated from data in column A. (DP :1 end point by derivative. expected derivative end point, end point by graph. 32 all samples the value is 7.78 i 0.030 ml. The results indicate that the observed deviations are random. Table XIV reveals the accuracy obtained for a representative num- ber of determinations. The results indicate that in aqueous formic acid, potentiometric titration is accurate and reproducible. For solutions down to 10-3 M in chloride the error is within the 0.1% level with a maximum error of approximately i 0.3% for any one determination. To obtain these results meticulous attention was paid to analytical tech- niques. Only by allowing the system to reach equilibrium after the addition of each increment of titrant could smooth changes in the deriva— tive be obtained. For solutions 8, and 5 in Table XIV, the calomel half cell had been thermostatted. This resulted in a further stabiliza- tion of potentials during a titration. Allowing the electrode system to stabilize itself prior to titration by stirring for several minutes in the solution to be titrated was helpful. A reinvestigation of the loss of chloride accompanying extraction was undertaken. Since a clean separation of the two phases could not be effected, carbon tetrachloride was always present in the aqueous solution to be titrated. Its presence interfered with the potentio- metric titration. In the course of titrating chloride with silver, the chloride ions are strongly adsorbed on the silver chloride precipi- tate(37). Therefore, a reasonable rationale for this behavior is that carbon tetrachloride coats the forming precipitate and thus effectively removes it from solution. This destroys the dynamic equilibrium between the chloride ion adsorbed on the precipitate and free chloride ions in the solution. Furthermore, the carbon tetrachloride appeared to coat the silver electrode. 33 Table XIV. Accuracy of potentiometric titration of chloride Solu- Meq. Cl Meq. Cl M NaCl Sample tion. Déf. M AgNOs taken found % Error 0.08107a’c 1 1 7.88 0.02612 0.2087 0.2088 0.0888 2 7.82 0.2083 —0.1958 3 7.82 0.2083 -0.l958 8 7.83 0.2085 -0.0977 average 7.83 0.2085 -O-O977 0.080951%C 1 2 7.88 0 02612 0.2088 0.2088 0.1957 2 7.82 0.2083 -0.0888 3 7.83 0.2085 0.0888 average 7.83 0.2085 0.0888 0.02886a’c 1 3 8.78 0.02610 0.1239 0.1237 -0.1618 2 8.76 0.1282 0.2821 average 8.75 0.1280 0.0871 0.1003d’f 1 8 13.37 0.02988 0.3997 0.3995 -0.0500 2 13.37 0.3995 -0.0500 3 13.80 0.8008 0.1751 average 13.38 0.3998 0.0250 0.10082’f 1 5 10.10 0.02988 0.3010 0.3018 0.2658 2 10.08 0.3012 0.0688 3 10.07 0.3013 0.0996 ,average 10.08 0.3013 0.0996 apipet volume = 8.988 ml. bpipet volume = 8.992 ml. C5 cc. of HCOOH. dpipet volume = 3.985 ml. epipet volume = 2.998 ml. f 10 cc. of HCOOH, calomel temp. = 23.00 i 0.050. 38 Removal of the carbon tetrachloride was accomplished by either of two methods: removing it from the bottom of the titration beaker with an eyedrOpper or re-extracting each aqueous layer with a small portion of petroleum ether. For kinetic runs the latter method was used. The insolubility in hydrocarbon solvents of the compounds to be studied kinetically precluded them as replacements for carbon tetrachloride. Due to its instability chloroform was not considered. Methylene chlor- ide separated cleanly, but an approximate 0.5% chloride loss was ob- served. Therefore, it was considered unsatifactory. Milliequivalents of chloride titrated after sample extraction are listed in Table XV. The meq. of chloride are calculated by both methods for obtaining the end point. The data reveal that the meq. of chloride recovered are randomly distributed about the meq. taken. This conclusion is supported by the following: the percentage deviations using the graphically determined end points are small and random, and the same end point distribution was obtained for un-extracted samples. Therefore, the loss of chloride occurring during sample extraction must be insig- nificant, well within the 0.1% level. This conclusion is further sup- ported by data to be presented later. The average end point potential obtained for 56 unextracted samples was 265.13 mv. while the corresponding value for 21 extracted samples was 268.03 mv. Only 5 samples showed deviations greater than i 3 mv., and only l6 samples showed deviations greater than i 2 mv. These fluc- tuations can be reduced by thermostatting the calomel half cell and keeping approximately constant the volumes of solutions to be titrated. Nevertheless, either of these average end point potentials agrees well with the theoretical value for the equivalence potential of 266 mv. (38). 35 Table XV.a Titration of chloride after sample extraction Sample A Emf Meq.AFound Meq.BFound %EXror %7Egror 1 7.76 7.772 268 0 0.2025 0.2028 0.2875 0.3960 2 7.76 7.780 263.5 0.2025 0.2020 0.2875 0.0000 3 7.76 7.785 265.5 0 2025 0.2021 0.2875 0.0500 8 7.78 7.780 260.0 0.2020 0.2020 0.0000 0.0000 5 7.78 7.760 268.0 0 2020 0 2025 0.0000 0.2875 6 7.78 7.780 268.3 0.2020 0 2020 0.0000 0.0000 7 7.75 7.782 268.0 0.2023 0.2021 0.1885 0.0500 8 7.73 7.735 268.5 0.2018 0.2019 -0.0990 -0 0500 9 7.75 7.736 268.5 0 2023 0.2019 0.1885 -0.0500 10 7.76 7.738 265.3 0.2025 0.2020 0 2875 0.0000 11 7.78 7.728 265.3 0 2020 0.2017 0.0000 -0.1885 12 7.75 7.780 268.3 0.2023 0 2020 0.1885 0.0000 aMeq. c1 taken = 0.2020; M NaCl = 0.08052; pipet volume = 8.988 ml.; 15.1191103 = 0 02610 i 0.00002. A = end point by derivative. B = end point from graph. It became necessary to accurately titrate solutions down to 10-4 M in chloride. Precise titration of solutions less than 10’3 M in chloride is difficult. As the chloride concentration decreases, titra- tion curves become progressively flatter and exhibit less "break" in the region of the equivalence point (35,36). The rise or fall in the potential in the neighborhood of the equivalence point is dependent upon the concentration of the solutions to be titrated and upon the solubility product of the precipitate (35, 36). At these concentra— tions the influence of the solubility of silver chloride upon the total ion concentration near the equivalence point may not be neglected, and, therefore, the silver ion concentration shows no sudden increase near 36 the equivalence point resulting in the slow rate of potential change in this region (35,36). For solutions varying from 5 x 10—4 to 1 x 10—3 M in chloride, two methods of obtaining the end point were attempted: graphical analysis and titration to a preset potential. Using the second method, it has been reported (37) that chloride concentrations of 10-4 M and 10-5 M can be determined with an error of l and 10% respectively. Shiner (38) has reported the accuracy of the method to be well within the 1% level for solutions down to 10.4 M. One set of data in the paper reveal the average error in the titration of a 10'4M solution to be 0.1% with a precision of i 0.3%. Since the equivalence potential is temperature dependent, it is necessary to thermostat the calomel half cell and maintain a reasonably constant room temperature. It is necessary to reproduce or eliminate junction potentials. Results obtained by graphical analysis of titration data for solu- tions 1.5 x 10'3 to 2 x 10"4 M in chloride are listed in Table XVI. For solutions containing 0.08 to 0.1 meq. of chloride end points were esti- mated by the derivative technique. This was done by taking the mid point of that increment of titrant giving the largest value of 85/80 around 265 mv. The reliability of this method is at best questionable. The uncertainty in location of the end point by graphical analysis increases as the chloride concentration decreases. This results from the necessity of compressing the axes due to increasing linearity. This method ap— pears to be accurate to about 0.8% in this concentration range. Titra- tion curves obtained from data for chloride solutions ranging from 5 x 10"5 to l x 10’4 M begin to approximate straight lines. The following 37 686.6- 666.6 6H6.6 666.6 omooo>m NHH.6- 666.6 666.6 6H6.6 666.6 86.6 m 6H6.6 666.6- 666.6 666.6 6H6.6 66.6 6 666.6- 666.6 666.6 666.6 666.6 66.6 a 666.6- 666.6- 666.6 666.6 omooo>o 666.6- 666.6- 666.6 666.6 H66.6 666.6 6 668.6- 666.6 666.6 6H6.6 666 6 666.6 6 6.6.6 6.66 x 666.6 666.6- 666.6 666.6 866.6 666.6 66.6 6 886.6 66H.6 666.6 H6.6H 66.6H ommoo>m 666.6 666.6 66.6H 66.68 66.66 86.66 6 666.6- 666.6 666.6 66.6H 666.6 66.6 6 666.6 666.6- 66.6H 666.6 666.6 66.6 a 666.6 666.6 66.66 66.6H omopo>o - 66H.6 - H6.6H - 66.68 6 666.6 666.6 66.6H 66.6H 86.6H 66.68 N 66.6 6-6a x - 666.6 - 66.6H 66.66 - 666.68 H . 666.6 666.6- H66.6 666.6 66.6H omopo>o 666.6 Ham.o 666.6 666.6 666.6 666.6 6 668.6 866.6 666.6 H6.6H 666.6 66.6H m ~-6H x H46.6- 866.6 666.6 86.6H 666.6 666.6 66.68 a 666.6 666.6 666.6 66.6H 66.6a ommao>o 666.6- 664.6 66.66 66.68 66.68 66.68 6 668.6 666.6 66.6H 46.6H 66.66 66.66 m mma.6 666.6 66.66 46.66 H6.6H 66.66 a 666.6- 666.6 66.6H 66.6H ommoo>m - 668.6 - 66.6H - 666.68 6 666.6- 666.6 66.48 66.6H 66.6H 66.66 6 6.6.6 ~-6H x 666.6- 66H.6- -66.aa 66.6H 66.66 66.6H 66.4H H H66.H 6 a «68.x 6 .,~6a x 6 ~6a x 6 6 a oaaaom 8662 2 mcoaosaom ooapoaco 666866 6o coaeoaoa6 .H>x 66666 38 .66066 0666 omsuom mo .66 mm .m :6 60666 N u 0 .Ha 66.66 H .Ho> .666a .~-6a x 666.6 . n6666 mm .6 c6 aoaao 6 u 6 .66 66.66 a .6o> .6666 .~-6H x 666.6 a n6666. mo .6 aoa6 .ofioo ooaooaeo 6o .666 u 6 .HE 000.0H u .Ho> .6666 .686 666666 06 666666666 .< 8666 .6Hmo mumpoflco 60 .668 u 0 .H8 000.0H u .Ho> .6666 .6qumm .66 066 .66666 66660H56 mo .668 u 0 .He 066.4 n .Ho> .6666 .6HQEmm .66 OHQ .Hmowcampm .6cwoa 666 u m .HE M66.6 n .Ho> .666: .magamm .66 mm .0<\m< 66606 6:6 n.< n m4m.0 060.4 66666>m . 640.0 660.4 6H.0H m u 60m.0 HOH.4 06.0H m a.m.6 nuOH x . 60m.0 HOH.4 060.4 . 06.06 H m40.m : 000.0 m4o.m ommho>m 1 640.0 040.6 60.m m u 64H.0 m40.m m60.m m Hamno nuofi x u 64H.0: m40.m m40.m 60.m H mm0.~ .6 .6.6 6 ,.6 ~66 x 6 ~66 x 6 ~66 x 6 6 . a oHaamm 6666 a .Aooacaacoov .H>x 66666 39 procedure was used in an an attempt to obtain end points from these curves providing they were not straight lines. 1) At any point on the curve before the end point a tangent to the curve was constructed. 2) At any point on the curve after the end point, a tangent to the curve parallel to the first was drawn. 3) At an assumed end point a tangent was constructed to the curve and projected until it intersected those of 1 and 2. 8) The end point was taken as the mid point of the projection of these intersections on the X- axis. The data in Table XVII indicate that this method is accurate to about 1% for solutions 10-4 M in chloride. For the 5 x 10-5 M solution only one out of four curves could be analyzed. Neither of these methods appeared adequate because of the error and the large amount of time required for a given determination. Table XVI reveals that the degree of accuracy observed for those samples titrated to a preset potential is comparable to these graphical methods. This was further substantiated by experimental results obtained prior to thermostatting the calomel half cell. Comparing the percentage deviations of the extracted and unextracted samples, Table XVI further supports the previous conclusions concerning the extraction procedure. When titrating samples to a preset potential the calomel half cell was thermostatted and the initial volume of solutions to be titrated was 100 t 5 ml. Table XVIII lists the results of a representative num- ber of titrations. It can be seen that the end point potential is ap- proximately constant with deviations of approximately t 0.5 mv. Some of 80 the potentials were obtained after the correct volume of titrant had been added. A large number of the potentials were obtained by bal- ancing the potentiometer after titration to 265 mv. From the data it would appear that these potential fluctuations are serious for only four samples. These results indicate that chloride solutions down to 10‘4 M can be titrated with an average error of approximately 0.2%. Solutions to be titrated were prepared by adding 10 ml. of formic acid to 80 ml. of water and pipetting in a 10 ml. aliquot of standard sodium chloride solution. Table XVII. Titration of dilute chloride solutions3 Meq. Cl Meq. C1 Sample U.E. E. End Point taken found % Error (m1.) x 103 x 103 1 - 9.95 9.993 9.95 -O.8OO 2 - 9.93 9.93 -O.601 3 - 9.98 9.98 -0.500 8 - 10.21 10.21 2.20 5 - 10.58 10.58 5.87 6 - 10.05 10.05 0.601 aMAgN03 = 1.000 x 10'3; M NaCl = 9.997 x 10‘4; pip. vol. = 9.996 ml. Table XIX reveals that the equivalence point potential is dependent upon the formic acid concentration. Doubling the formic acid content of the titration solution reduced this potential by approximately 5 mv. This change in the equivalence point potential was measured after the addition of approximately the correct volumes of silver nitrate to solutions containing 10 ml. of formic acid. 81 Table XVIII. Titration of limiting chloride concentrations to preset potentiala Meq. C1 Meq. Cl M NaCl Sample E.P taken found % Error Emf ' ml x 102 x 102 1.023 b 1 2.565 1.022 1 023 0.0978 265.00 x 10'3 2 2.561 1.022 0.0000 268.90 3 2.580 1.013 -0.8806 265.50 8 2.550 1.017 -0.8892 265.90 5 2.580 1.029 0.6889 265.20 average 2.559 1.021 -0.0978 2.085 b 1 5.130 2.088 2.087 0.1867 265 00 x 10'3 2 5.115 2.081 -0.1867 265.60 3 5.122 2.088 0.0000 265.13 8 5.120 2.083 -0 0889 265.13 5 5 120 2 083 -0.0889 265.13 average 5.121 2.083 -0.0889 3.058 C 1 7.685 3.053 3.050 -0 0983 265.18 x 10 3 2 7.670 3.060 0.2293 265.17 3 7.660 3.056 0.0983 265.20 8 7.67 3.060 0 2293 265.27 5 7.68 3.068 0.8258 265.00 6 7.66 3.056" 0.2293 268.00 7 7.66 3 056 0 2293 263.00 8 7.655 3.058 0.0328 268.80 9 7.680 3.068 0 8258 268.05 10 7 660 3 056 0.0983 263.00 11 7.650 3.052 -0.0328 263 00 12 7.655 3.058 0;0328 262.60 13 7.63 3.088 -0.2988 268.53 average 7.66 3.056 0.0983 1.018 1 2 580 1.018 1 013 -0.8912 265.00 x 10‘3 C 2 2.555 1.019 0.0982 265 00 3 2 555 1.019 0.0982 265.38 average 2.550 1.017 -0.0982 2.036 1 5.090 2.035 2.031 -0.l966 265 00 x 10‘:5 C 2 5.100 2.035 0.0000 266.00 3 5.102 2.036 0.0891 265.10 average 5.097 2.038 0.0891 aN.B.S. volumetrics used, 10 cc. sample, tit.vol. 100 i 5 m1., room bPip. vol. CPip. v01. temp. 23 i 10, calomel cell temp. 23.30 t 0.050, M AgN03 = 3.990 x 10‘3. 9.996 ml. 9.997 ml. Table XIX. Dependence of end point potential upon formic acid concen- trationa M NaCl Sample HC808 A8803 Emf Avg. Emf Migkegl Mfgungl 2.005 b 1 5 7.882 265.15 x 10‘3 2 5 7.885 265.50 265.55 3 5 7.900 266.00 8 10 7.890 260.00 5 10 7.895 262.00 6 10 7.890 260.62 7 10 7.895 260.80 8 10 7.900 259.50 260.15 9 10 7.895 259.30 10 10 7.895 259.80 11 10 7.890 259.80 12 10 7.870 260.00 0.1003C 1 10 7.972 262.80 0.5001 0.5008 2 10 7.976 260.50 0.5007 3 10 7.975 262.50 261.18 0.5006 8 10 7.972 262.00 0.5008 5 10 7.970 258.00 0.5003 average 0.5008 aTit. vol. = 100 t 5 m1. bPip. vol. 19.98, M AgNOg = 5.076 x 10_3 calc. v01. AgN03 = 7.892. ) 8.986, MAgNO3 = 6.277 x 10‘2. CPip. vol. The last major problem encountered was the occasional shift in the equivalence point potential observed upon introduction of a new salt bridge. Such shifts were recognizable from the analytical results. Errors were reproducible for any given chloride concentration. However, the relative error changed as the chloride ion concentration was varied. This result is not unreasonable, since titration curves are not identical at these limiting concentrations. The value of the equivalence poten- tial was checked by adding the calculated volume of standard silver nitrate to standard sodium chloride, or by titrating solutions containing 83 at least 0.2 meq. of chloride. It is strongly advised that such per- iodic checks be made when using this procedure. During kinetic runs many such titrations were performed. The previous results are repre- sentative, and by no means the best obtained; in some instances end point potentials were reproducible to within i 0.2 mv. In summary, the error in potentiometric titration of solutions containing more than 0.1 meq. of chloride is at the 0.1% level. By stringently observing the necessary precautions, solutions down to 0.01 meq. can be accurately titrated to a preset potential. In the present work, the resulting average error was usually less than 0.2%. The accuracy attainable by the Volhard method is dependent on indicator concentration. For chloride concentrations ranging from 0.1 to 1.0 meq., the accuracy might reasonably be expected to vary from 1% to 0.1%. In the opinion of the author, lower chloride concentration cannot be titrated with any reasonable degree of accuracy. Because of its precision, accuracy, and simplicity, the potentio— metric method is clearly preferable to the Volhard method. By taking the necessary precautions, the recovery of chloride after extraction is nearly quantitative. If the proper choice of extraction solvents is made, potentiometry can be used to follow kinetics in other solvent systems (38). IV. Kinetics In the present studies, it was imperative that the solvolysis pro- ceed by the 8N1 mechanism. Therefore the choice of solvent was criti- cal. The mechanistic ArCHZOH + HCl (1) Since a measurable equilibrium was established during solvolysis of the more reactive compounds, the unimolecular rate constant, k1,was obtained from the integrated equation for a reaction which is first order forward and second order backward. x8 on8 + x(Ao — xe) k t = 1n 2 1 (2_'__—Aoe ___)_(;) ( AO(Xe __ X7 ) ( ) where A0 is the initial concentration of ArCHZCl x is the concentration of HCl at time t Xe is the concentration of HCl at infinite time. Usually 8, 9 or 10 samples over a time period of 10 to 12 hours were taken during kinetic runs of a-naphtnylcarbinyl chloride and its deuterated analogs. Due to the appearance of turbidity, infinity titres were obtained after 22 to 28 hours. At this time solvolysis had pro- ceeded through approximately six half—lives. Except for run 13a (Table XX) some turbidity was always present. The infinity samples for run 13b taken after 51-52 hours had just begun to show the presence of 86 Table XX. Rate and equilibrium constants for solvolysis of d—naphthyl- carbinyl chloride Run A0 x 103 [XJeq. x 103 ks:clgi % rx. Keq; x 102 1 8.968 7.265 8.63 81.0 3.11 1a 8.968 7.271 8.62 81.1 3.12 lb 8.968 7.253 8.65 80.9 3.11 2 8.613 7.112 8.55 82.6 3.39 3 8.718 7.163 8.62 82.2 3.30 8 8.573 6.927 8.57 80.8 2.92 8a 8.573 6.988 8.52 81.0 2.97' 8b 8.573 6.918 8.61 80.6 2.88 8c 8.573 6.919 8.59 80.7 2.89 8db 8.573 6 927 8.62 80.8 2.92 8 9.382 7.811 8.80 79.0 2.79 12 9.615 7.600 8.35 79.0 2.87 12a 9.615 7.633 8.31 79.8 2.98 12b 9.615 7.609 8.38 79.1 2.89 12c 9.615 7.563 8.80 78.7 2.79 12d 9.615 7.598 8.36 79.0 2.85 l2e 9.592 7 600 8.37 79.2 2.90 13a 8.981 8.889 8.83 90.1 8.10 13bC 8.981 8.559 8.32 91.5 8.92 average least squares 8.89 aSub-runs calculated for changes in x, xeq , or A0. bEach value of x increased by 0.2%. CUsed as the rate constant for run 13. 87 turbidity. Usually infinity titres were obtained for three samples. The maximum deviation of the individual values of Xeq. from their average in any run was usually within 0.5% and only for run 12 did this value rise to 1%. Rate constants were obtained by linear least squares analysis. Equation 2 and the linear least squares equation were programmed, using Fortran notation, and the raw data were processed on a Control Data 3600 computer. Tables XX, XXI, and XXII list the unimolecular rate constants for d-naphtnylcarbinyl chloride, a-naphthyl- carbinyl chloride —8-d, and d-naphthylcarbinyl chloride-0,0- d2. The average least squares rate constant for a-naphtnylcarbinyl chloride is 8.89 x 10.5 secrl. The maximum deviation is i 0.17 x 10.5 sec.—1 and the average deviation is i 0.11 x 10’5 sec.'1. The present value compares favorably with the value 8.8 x 10.5 sec._1 reported by Dewar and Sampson. An estimate of the influence of changes in x, xeq.’ and AC on the rate constant can be seen from the sub-runs in Table XX. Run 8d reveals that increasing each value of x by 0.2% increases k by 1%. Reduction of AG by 0.2% reduces k by 0.5% (run 122). Comparing la and lb reveals that decreasing Xe by 0.25% increases k by 0.65%. In- creasing Xeq. by 0.92% decreases k by 2% (runs 12a and 12c). Taking the activation energy as 25 kcal./mole (88), it can be shown that temperature control should be i 0.10 for a 2% error in k. Since temperature control was better than i 0.010, contributions to the error due to temperature fluctuations were negligible. The estimated error in k due to error in time measurements is less than 2%. As pre- dicted (85) and verified by the above data, the largest source of error is related to the analytical precision. It is not known whether the observed precision in k is the best that can be obtained with the present 88 analytical method or whether other problems contribute measurably. Shiner (38b) has reported rate constant precision of i 8% using potentio- metric titration to follow the appearance of halide ion, with initial organic halide concentration of approximately 0.05 M. Part of this error may have been caused by a small mass law effect which prevented the reaction from strictly obeying the first order kinetic rate expres- sion. ' Table XXI. Rate and equilibrium constants for solvolysis of d-naphthyl- carbinyl chloride-B-d. Run A0 x 103 [x] x 103 k x 105 % rx. K x 102 89- sec.'1 GQ- _ 5 8.561 6.989 8.58 81.2 2.97 6 9.105 7.290 8.53 80.1 2.93 7 9.215 7.853 8.85 80.1 3.15 average least squares 8.51 Table XXII. Rate and equilibrium constants for solvolysis of d—naphthyl- carbinyl chloride-0,0-dé. Run A0 x 103 [XJeq. x 103 k x 10? % rx. Keq. x 102 sec. 9 9.815 7.758 3.31 79.0 2.92 10 10.39 8.086 3.29 77.8 2.77 11 9.972 7.717 3.35 77.8 2.68 average least squares 3.32 Due to the difficult solubility of 8-bromo-a—naphthy1carbinyl chloride and its increased rate of solvolysis, a thorough kinetic study was not made. Since a measurable equilibrium appeared to be established, 89 the rate constants were calculated using Equation 2. The accuracy of the rate constants may be less than the results indicate (Table XXIII). Table XXIII. Rate constants for solvolysis of 8-br0mo—0—naphthyl— , carbinyl chloride and 8—methyl—a-naphthylcarbinyl chloride. Compound A0 x 103 [x] x 103 k x 105 V % rx. eq. sec.-1 8-bromo 5.225 8.888 6.15 93.6 8-bromo 5.022 8.736 6.11 98.3 8-metnyl 5.18 8.83 3.8 x 102 88-93 The very fast rate of solvolysis of 8-methyl-d-naphthylcarbinyl chloride, combined with its low rate of solubility, prohibited accurate rate studies. The rate was obtained by estimating the half-life. Toa first approximation, the equilibrium constant and percentage reaction should be the same for a—naphthylcarbinyl chloride and its deuterated analogs. Obviously, neither of these terms should be con— centration dependent. However, Tables XX, XXI, and XXII reveal that both the equilibrium constant and percentage reaction vary with initial concentration, and a systematic trend is exhibited. Decreasing the initial concentration of organic chloride from 1.039 x 10.2 M to 8.981 x 10.3 M increases the percentage reaction from 77.8% to 91.5% and the equilibrium constant from 2.77 x 10'2 to 8.92 x 10‘2. However, Table XX reveals no such systematic trend in the rate constant. Therefore it is necessary to examine the assumptions made in de- riving equation 2, the mechanistic implications of equation 1, and the effects of turbidity. 50 Let us first assume that equation 1 is valid and consider the as— sumptions implicit in equation 2. Let equation 3 be a general reaction scheme representing 1. k1 < k2 > B + c (3) The general differential rate expression is dx - k [A 1 RI 12 where [Bo + xe][Co + xe] [Ao ' Xe] K = kl/kz = assuming [H20] to be constant and B0 = Co. For the completely general case, Bo and Co are not necessarily equal to zero. Equation 8 is easily reduced to equation 5 which is in standard form. v=v2 Tar.z dV k1. -__—’ = 1 dt a2~~v2 T— (S) v=v1 . ‘ T=O where 1 2 66 + 66.7 7 V = [X] + (K + 280) 2 v2 < az. Equation 2 is easily derivable from equation 5 by assuming that B0 and Co are identically zero. Therefore, for equation 2 to be rigorously correct, there must be no initial concentration gradient. Since a- naphthylcarbinyl chloride and its deuterated analogs were not readily soluble, one source of error is immediately introduced. The time 51 required to dissolve the compound, 8 to 9 minutes, varied both with the amount of material and its crystalline form. Since vigorous shaking was required, the volumetric flask could be filled to only about 60% capacity, introducing other sources of error. Initially concentration gradients existed and the rate of solvolysis was not uniform. Due to the ex- tremely vigorous agitation required, the loss of a small amount of solu- tion from the tightly stoppered volumetric flask was occasionally noted. A non—uniform rate of solvolysis resulted from the decrease in the temperature over the time required to prepare the solution and fill and seal the ampoules. This time varied from 15 to 17 minutes. The first samples were taken after approximately 60 minutes, which correSponded to about 15-20% solvolysis. Thus these effects may be partly obscured by the long half-life. However, the rate constants calculated by equa- tion 2 will undoubtedly reflect some of these effects. The magnitude of this effect is undoubtedly increased for 8-br0mo- 0-naphthylcarbinyl chloride due to its increased rate of solvolysis and its low rate of solution; Twenty-two to twenty-five minutes were re- quired to prepare a 5 x 10-3 M solution. The time required to dissolve 8-methyl-0-naphthylcarbinyl chloride was longer than its half—life. The general condition B0 = C6 5'0 yields equation 6. 1:1{61/2 fix 53)}: 201/2k1t + 1n (61/2 4» d) 0172 - (x + 8) ‘K, 9172 .. ¢ where (D I 2 — K1104] - [13.12 . (_.,___K * 290]) (6) K + 2[Bo] 8: 2 52 ([801 + may [80’] ' [X] K :- eq. [80’] = [A0] - [xt=t£ and [B0] = [xt=t]. The rate constant is influenced in a complex manner by initial concentration and temperature gradients, which effectively make Bo and Co not zero at T = 25.0080. In principle, this error could be eliminated by use of equation 6. This was not attempted because of the uncertainty in the analytical results for chloride concentrations below'lO—4 M and the variance in the equilibrium constant. We now consider whether the solvolysis reaction is adequately represented by equation 1. Assuming no turbidity, we write the follow— ing mechanism: k + .. 471:. ArCHZ + (:1 (7a) "1 ArCHZCl + k2 + ArCH2 + H20 <.————:> ArCHZOH + H (7b) “-2 . <7) k ArCH;'+ HCOOH 3 > ArCHZOOCH + H+ (7c) k ArCHZOH + HCOOH .——$a> ArCHZOOCH + H20(7d) <— k-4 The equilibrium constant for the solvolysis reaction is given by: [ArCHZOH][H+][C1-] K = K x = 79 X 7b [ArCHZC1][H20] (8) Equation 8 is the same equilibrium equation as that obtained from equa- tion 1, providing [H+] is constant. Clearly [x]eq is really [Cl-Jeq , not [HC1]eq . 53 Let us examine the effect of formate on the equilibrium constant. The correct stoichiometry would then be UMGQGU i-[Ammgbdu = [cfl (% Assuming that at equilibrium [01-] = [ArCHZOH], equation 9 suggests that the equilibrium constant would change with initial concentration of organic halide if esterification occurs. We write _ [ester][H20] 7d - [alcohol] (10) Rearranging equation 10 in terms of [ester] and substituting in equa- tion 9, we obtain [ArCH on] = [C1-ng' (11) 2 eq. (1 + K7d[Hzo]‘fi Substituting equation 11 into equation 8 gives [c1‘12 a 99: (12) [ArCH201]eq.([HZO] + K7d) Making the reasonable assumption that [H20] is constant, equation 12 reveals that the formate ester has no effect on the calculated equilib- rium constant at a given water concentration. However, as the water content of the solvent is changed, K should change unless [H20] << K7d or [H20] >> K7d° Dewar and Sampson (82) found that for the more reactive compounds equilibrium appeared to be reached whether the alcohol and gaseous hydrogen chloride, or the arylmethyl chloride, was dissolved in formic acid. The equilibrium constant was approximately constant over a three- fold variation in water content (0.38 M - 1.2 M). Therefore, they 58 concluded that the reactions producing formate ester were relatively slow, or that the alcohol-formate equilibrium strongly favored the alco- hol. The problem needs to be reinvestigated, since these authors re- ported their equilibrium constants accurate to i 10%. For half of the compounds for which an equilibrium constant was reported, changing the water concentration from 1.2 M to 0.38 M increases the equilibrium constant in accord with equation 12. However, the change is in the opposite direction for the remaining compounds. Neglecting equations 7c and 7d, we consider the differential rate law derived, assuming the solvolysis mechanism is described by equations 7a and 7b. We write - d[Ar:EZCl] = k, [ArCHZCIJ - k_1[ArCH2+][01'] (l3) and W = k, [AFCHZCl] - k_l[ArCH2+][Cl'] (l8) -k2[ArCHZ+][HZO] + k_2[ArCH20H][H+] Applying the steady state assumption, solving for [ArCH2+], and sub— stituting into equation 13, we obtain -d[ArCHzCl] = kl[ArCH2Cl] _ k_1[c1‘]( dt k1[ArCHZCl] + k_,[ArcH201i][H+]) k_1[c1'] + kziHZOJ (15) Assuming that k_2 [ArCHZOH][H+] > k1[ArCHZCl] and k2[H20] > h_1[c1'] and noting that k_2/k2 = 1/k7b, K7b = K7a/X, and K7a = k,/k_1 we obtain —d[ArCHZCl] = k11ArCH20HltH*ch1'l dfl k1[ArCHZCli - KTHZOJ (16) 55 Equation 16 is equivalent to equation 8 on the condition that both [H+] and [H20] remain constant. Furthermore, equation 16 predicts that the rate of solvolysis should increase with increasing water content of the solvent. Such an increase was observed by Dewar and Sampson (82). The previous assumptions require that k_1 be the rate determining step for the reverse reaction with equation 7b a pre-equilibrium step. It is easily shown, assuming equilibrium conditions, that the inverse as- sumption leads to a different rate law. The experimental results there- fore support the validity of the present assumption. We can conclude on this basis that equation 1 is a valid representation of the solvolysis. We now examine the rate expression including equation 70. Apply— ing the steady state approximation and the previous assumptions we ob- tain —d[ArCH201]_ J k1[ArCI-IZOH][H+][Cl-] dt - k1 [ArCHZCl - K([H201 + ké/kz) (17) I where k3 = k3 [HCOOH]. Equation 17 shows that the rate of solvolysis is actually affected by the rate of esterification. Since kg‘will remain essentially con- stant over various water concentrations, its neglect will introduce a constant error in the rate constant (k1). It is also apparent that unless the equilibrium between formate ester and alcohol strongly favors the alcohol, or that k3 << k2, an error is introduced due to erroneously assumed stoichiometry. Equation 9 reveals that even if a finite equi- librium is immediately established, an error is introduced, the magni- tude of which, however, decreases as the solvolysis proceeds. Since it is reasonable to expect esterification to occur (equation 7d), the rate constant obtained will differ from the rate constant for solvolysis 56 based on equation 1, and equation 70 should introduce some deviation in k within a run. We now consider the influence of turbidity on the equilibrium constant, percentage reaction, and rate constant. From limited re— sults of studies of the insoluble products formed in the solvolysis of a-naphthylcarbinyl chloride, the following equations are postulated. kla ArCH2+ + ArCHZOOCH > ArCHZArCHZOOCH (l8) k ArCH2+ + ArCHZOH 9 > ArCHZArCHZOH + HCOOH k. (19) ——£#> ArCHZArCHZOOCH k ArCH2+ + ArCHzCl 2° > ArCHZArCH201 (20) Dewar and Sampson, using initial arylcarbinyl chloride concentra- tions below 8 x 10'3 M, observed no turbidity for 15 to 20 half-lives. They concluded that solvolysis could be studied without interference from this source. The effect of equations 18, 19, and 20 is not obvious. Let us re-examine d[ArCHé+]/dt, including equations 18 through 20. d[ArCH2+] dt = k1[ArCHZCl] - [ArCH2+] (84[01’J - k2[HZO] - ks) + (21) k ArCHZOH] [H+]- [ArCH2+] 21 ki([ArCHZOOCH]+[ArCH20H]+[ArCHZC1]) -21 1 In deriving equation 21 the following assumptions were made: (1) The solubility of the monomeric formate has not been exceeded. (2) It is entirely reasonable to expect the carbonium ion to attack the alcohol. Since the product studies indicated the absence of multi-substituted alcohols in the precipitate, these must have remained in solution until they were esterified. This is reasonable in view of the high solubility 57 of a—naphthylcarbinol. (3) The ionization of any substituted 0— naphthylcarbinyl chlorides remaining in solution has been neglected. (8) The rate constants kle, klg, and kzo are to a first approximation equal. (5) Equations 18, 19, and 20 are actually a composite of re- actions leading to different positional isomers and thus are better represented by summations. Clearly, if all ki's are small, equation 21 requires that the ap- pearance of turbidity should be sensitive to the initial concentration of a-naphthylcarbinyl chloride. The results of Table XXIV confirm this hypothesis. The data show an extremely strong dependence between the time for appearance of turbidity and initial concentration. At low concentrations of a-naphthylcarbinyl chloride and early in the sol— volysis equation 17 should be obeyed, the effect of equations 18 through 20 becoming significant only with additional time. As the initial con- centration of a-naphthylcarbinyl chloride increases, the effect of these reactions should appear earlier. This observation was qualita- tively confirmed since the amount of turbidity present when infinity titres were taken appeared to increase with increasing concentration of the halide. In the present studies, percentage reaction was defined as [01'] % Rx. = eq’ (22) IKrCHZCIJinitial and the equilibrium constant as 2 I ([H o] ) [XJGCI K = K 2 + K7d = . (23) [101-1x18, The observed trend in these terms is now obvious. At "equilibrium" equations 18 and 19 have the effect of producing more ionization. 58 However, equation 20 both reduces the concentration of solvolyzable chloride in solution and the [Cl—]. Therefore, the amount of unsol- volyzed halide is less than the stoichiometric value based on equation 7. From a statistical viewpoint the effect of equation 20 increases with increasing concentration of the organic halide. Thus the per- centage reaction and the equilibrium constant should decrease with increasing initial concentration of organic halide. Table XXIV. Study of time for appearance of turbidity as a function of initial concentration of a—naphtnylcarbinyl chloride. Concentration (moles/l.) Solventa Time (hours)‘ 0.12 0.25 M 1 0.095 0.8 .8 1.2 0.058 0.28 M 0 - 13.5 0.031 0.83 M 19 0.016 0.83 M 20 0.012 0.32 M 22 - 28 9.5 x 10-3 0.83 M 38 - 88 9.8 x 10'3 0.28 M 27 - 30 5.3 x 10'3 0.83 M 72 8.8 x 10'3 0.28 M 72 8.981 x 10‘3 0.32 M 51 aEstimated to be minimum water content. It is easily shown that equations 18 through 20 affect the rate constant. The rate of reaction, neglecting the backward reaction, is given by A[Cl 1 At = k, [ArCH2C1] (28) The left side of equation 28 is eXperimentally determined. The 59 concentration of arylmethyl chloride at time t is calculated from the relation [ArCH201]t=t = [ArCHZCl], - [c1‘]t=t (25) nitial However, the stoichiometry is no longer correct because of equation 20. The correct relation is [Ar082c1]t=t = [ArCH201]ini - [ArCHZArCHzcnt=t - [01 Jt=t (26) tial Equation 26 shows that k must change to compensate for the effect of neglecting equation 20. Equation 21 reveals that equations 18 through 20 would affect the bimolecular (k_2) term, by reducing its contribution to the rate of solvolysis. Before visible turbidity develops, equations such as l8, l9, and 20 may occur. This would also introduce errors in the rate constant. Table XXV lists the calculated values of kH/kD. Since the differ- ence in rate constants between a-naphthylcarbinyl chloride and a—naphth- ylcarbinyl chloride-8-d is less than either the maximum or average de- viation of the former, the isotope effect is insignificant. Considering the uncertainty in the rate constants, the 0-deuterium isotope effect must be considered as normal. Dewar and Sampson (82) observed that the solvolysis rate of 0- naphthylcarbinyl chloride was 17 times greater than that of the B—iso- mer. From correlation of rate with delocalization energy, they con- cluded that the rate of the d-isomer was actually retarded. They argue that maximum resonance stabilization of the incipient carbonium ion in the transition state requires the hydrogens of the exocyclic -CHZ+ group to be approximately co-planar with the ring, as shown in Figure 3. 60 Such an effect would require an abnormally close approach between one of the methylene hydrogens and the peri hydrogen, resulting in an in- crease in (T bond energy in the transition state. The resulting strain energy was estimated to be 2.5 kcal. Table XXV. Relative rate ratios of deuterated and substituted d-naphthyl- carbinyl chlorides. Compound . kH/RD ke/kH 8-d 0.996 i 0.05 0,0-d2 1.35 8-bromo 1.37 8-methyl 85 Figure 3. Carbonium ion representing the transition state for the solvolysis of a-naphthyl carbinyl chloride. From Dreiding models the H'-H non-bonded distance is.estimated to be 1.9 3., which is well within the sum of the van der Waals' radii for two hydrogen atoms, 2.8 R. It appears reasonable to suggest that such a compression would effectively decrease the out-of-plane bending vibration of at least one of the a—hydrogens in the trigonal transition state. Such a reduction should decrease the magnitude of the a-deuter- ium isotope effect (13). Furthermore, substitution of deuterium in the 8 position might be expected to result in an inverse isotope effect. On this basis, and in view of the isotope effects reported by Melander (15) and Mislow (16) in related systems, an inverse isotope effect and 61 a low o-deuterium isotope effect would have been expected. An important consideration, neglected by Dewar in this particular paper, is that overlap is a cosine function (86). Rotating the exocyclic -CH2+ group out of the naphthalene plane by 60° reduces the overlap only 50%. Thus the increase in steric compression in the transition state can be partly compensated by rotation of the methylene group, with a small loss in resonance energy. Therefore any rate retardation might reasonably be expected to be small. On this basis, it appears reason- able to conclude that resonance stabilization of the transition state should be slightly increased for either of the deuterium analogs. Con— sequently, the magnitude of the isotopic rate ratios, kH/kD, should decrease. Steric strain may exist in the ground state of a-naphthylcarbinyl chloride. Figure 8 shows the preferred molecular conformation of a- naphthylcarbinyl chloride, based on examination of Dreiding models. H \ H H~0-C1 Figure 8. Preferred molecular conformation of d-naphthylcarbinyl chloride. Free rotation of the chloromethylene group is impossible. Since the maximum H--H non-bonded distance is estimated to be 2.8 8., which is just equal to the sum of the van der Waals' radii for hydrogen, oscil- lation of the chloromethylene group must result in an energy increase. Such increase may be partly compensated by an opening of the C9--C1-C(I angle. Deuterium substitutions in either the a-position or the 8-position 62 should decrease this energy. Therefore a normal isotope effect would be predicted. Fortuitously, the ground state and transition state ef- fects might cancel. The results of X—ray, chemical, and micro-wave studies support the existence of steric interaction between alpha substituents and the peri hydrogen. 1,5-Dinitronaphthalene is planar, but this is accomplished only by bending the nitro groups away from the peri hydrogen; the CQCIN and C10C5N angles are opened to 125° (87). 1,8-Dibromo- and 1,3-dichloro- naphthalene have been studied by Trotter (88). The data indicate, but by no means prove, that the alpha halogen atoms deviate by about 0.8 R. and 0.28 8., respectively, from the naphthalene planes. X—ray analysis of l-naphthoic acid (89) reveals that the carboxyl group is rotated about 11° out of the plane. In addition, there is a significant in- plane displacement of the C (aromatic) - C (carboxyl) bond away from the peri position, and the CQCICG angle is 128°. Hall and co—workers (50) were able to isolate an optically active form of l—(2—carboxyphenyl) naphthalene. Grubb and Smyth (51) attribute the restriction of internal rota- tion of a-methoxy- and a-ethoxynaphthalene over the corresponding 8- isomers, observed in micro-wave studies, to steric hindrance by the peri hydrogen. If such steric strain exists in the ground state, then the rate of solvolysis of a-naphthylcarbinyl chloride might actually be accelerated. In their treatment, Dewar and.Sampson have neglected solvation effects. Harrison, Kebarle, and Lossing (52) observed that the effect of substituents upon the stability of the benzyl cation in the gas 63 phase was greater than the substituent effect observed for the SNl solvolysis of Mcumyl chlorides studies by Brown (53). Rho in the gas phase was approximately -20, compared to -8.58 in solution. These authors concluded that the large difference was due not only to incom- plete charge formation in the transition state but also to solvation effects. Within experimental error, an excellent linear correlation was observed between the energies of ion-pair formation in the gas phase and gqrz, where qr is the fraction of positive charge at atom r. The fact that the a-naphthylcarbinyl cation did not deviate significantly indicates that the loss in resonance stabilization of the ion by steric interaction with the peri hydrogen must be small. Mason (58) has shown that serious error can result by correlating rates of solvolysis with only delocalization energies. Accounting for solvation effects, he was able to obtain good linear correlation for solvolysis of arylmethyl compounds in a number of solvents. An inter- esting theoretical conclusion is that the free energy of solvation should decrease with increasing charge dispersal. This would tend to increase the solvolysis rate of p-naphthylcarbinyl chloride, as com- pared to that of the a-isomer. Also, the 5N2 reaction with potassium iodide in acetone showed no evidence for steric retardation in the "peri" compounds. Dewar and Sampson (55) studied the rates of ethanolysis of a- and B—naphthyldimethylcarbinyl chlorides. The relative rate factor was 0.6. They concluded that this rate inversion was due to increased steric inhibition of resonance, and the a-isomer suffers a 17/0.6 or an additional 27 fold rate retardation. It is well known that comparison 68 of solvolysis rates obtained in different solvents can be misleading. For example, Okamoto and Brown (56) studied the rates of solvolysis of 0- and B—naphthyldimethylcarbinyl chlorides in 90% aqueous acetone. The a—isomer was 1.02 times as reactive as the fi—isomer. The rela- tive rate for the corresponding monomethyl compounds in 80% aqueous acetone was 2.56. These results suggest that both steric inhibition of resonance and solvent effects are important. However, steric effects are characterized by a rapid increase in magnitude with increasing bulk (20a). For the previous compounds, steric effects should increase in the order no methyl < monomethyl << dimethyl. The loss of resonance energy should increase in the same order, but its effect should be de- creased by the increasing intrinsic stability of the transition state. From studies of the rates of solvolysis of 972.E‘: and p-substituted M-cumyl chlorides and related compounds, Brown and co-workers (57) con- cluded that steric inhibition of resonance in the transition state could not be neglected, but that inductive and solvation effects were import- ant. The relative rate decrease, ko/kp, in the series methyl, ethyl, and isopropyl E-cumyl chloride was 0.18, 0.098, and 0.085, reSpectively. These were ascribed to increasing steric inhibition of resonance (57a). Later, Brown and Inukai (57e) concluded that the difference in the rela- tive rate acceleration factor of 26 for pfmethyl M-cumyl chloride, as compared to only 3.63 for the g-methyl compound, could not be solely due to steric inhibition of resonance. They concluded that the influ- ence of the g—alkyl substituents in hindering solvation of the incipient carbonium ion was also important. Baddeley and co-workers (58) have studied the solvolysis rates of monoalkylphenylcarbinyl chlorides and the basicities of the corresponding 6S amines. The order of reactivity decreased along the series: R = Me, Et, i—Pr, EfBu, corresponding to the order of increasing basicity. The authors concluded that the results are in accord with increasing steric interaction of the side chain with the ring. The complexity of steric inhibition of solvation is evident from the results of Chapman and co-workers (59), obtained from studies of the basic hydrolysis of g-substituted methyl benzoates. The entropy of activation is influenced by two effects, the "bulk-effect" and steric inhibition of solvation. In the series Me, Et, Pr, and E-Bu steric in— hibition of solvation increases, tending to make 88+ more positive. The "bulk effect", which increases in the same order, has the opposite effect on 88*. The two effects are clearly discernible but the relative dom- inance of either is solvent dependent. From this discussion, the conclusions reached by Dewar and Sampson concerning a rate retardation due to large strain energy in the transi- tion state in the solvolysis of a-naphthylcarbinyl chloride are prob- ably oversimplifications. Thus if the rate is actually retarded, part of the effect may well be due to steric hindrance to solvation (58,60). Also, steric strain in the ground state may compensate transition state effects. Furthermore, as the solvolysis reaction assumed more 8N2 char- acter the strain energy steadily decreased and finally disappeared in the 8N2 displacement by iodide ion in acetone (82). Thus the previous conclusions concerning the compensatory effects of isot0pic substitutions are not necessarily negated. Alternately, the substitution of deuterium for hydrogen may not produce an observable steric isotope effect in the compounds so far studied. The results of precise conductometric rate measurements must be obtained before any definite conclusions.can be drawn. 66 Table XXV reveals that substitution of a methyl group in the 8 position of 0-naphthylcarbinyl chloride increases the rate of sol- volysis by a factor of approximately 85, whereas the rate increase for bromine substitution is only 1.37. The large rate increase for 8-methyl— ci-naphthylcarbinyl chloride is attributed to steric strain in the ground state. The severe strain is probably compensated by bending the groups out of the naphthalene plane and away from each other. Figure 5 reveals that a considerable part, but not all, of this strain can be eliminated in the transition state. The H-oH non-bonded distance is estimated from Dreiding models to be 2 8. Thus complete relief of strain has probably not been achieved, and the observed rate increase is less than expected for complete relief of non-bonded interactions. Furthermore, it is not unreasonable to assume complete steric inhibition of resonance in the transition state. This would increase the energy of the transition state relative to that of a-naphthylcarbinyl chloride and thus mask the rate acceleration due to relief of ground state steric strain. Figure 5. Carbonium ion representing the transition state for the solvolysis of 8-methyl-d—naphthylcarbinyl chloride. The relatively small rate enhancement noted for 8—bromo-d-naphthyl- carbinyl chloride can be ascribed to several factors. First, Dreiding lmodels indicate, because of the increased C-Br bond length, that the non-bonded repulsions should be slightly less than that of the 8-methyl 67 isomer. Second, the bromine atom, being more polarizable, may be "elong— ated" and "whittled down" on the side facing the chloromethylene group, thus reducing steric strain. Third, the ground state of the bromo isomer may be considerably better solvated. Fourth, the close proximity of the bromine atom to the chloromethylene group may result in a strong inductive stabilization of the ground state. Brown and co-workers (57b) concluded from their studies of the rates of solvolysis of the g—, M-, and p- halogen E-cumyl chlorides that the increased rate reduction ob- served for the g—halogens was not only due to steric inhibition of reso- nance, but also to an enhanced inductive effect. For the previously discussed reasons, comparison of the 86bromo isomer with d-naphthylcarbinyl chloride does not yield in a true measure the rate enhancement due to relief of steric strain in the ground state. An alternate explanation, based upon non-classical structures, can be visualized (Figure 6.). These are considered unlikely; if methyl participation were important, the product might contain large amounts of acenaphthene. Also, participation by the bromine would be expected to be larger than that by the methyl group. Figure 6. Transition states for solvolysis of 8-methy1-a-naphthyl- carbinyl chloride and 8-bromo-a-naphthylcarbinyl chloride showing participation by the methyl group and the bromine atom. EXPERIMENTAL I. Synthesis A. Preparation of d-Naphthylcarbinol. To a 2 1., three—necked, round bottom flask fitted with a Tru-bore stirrer, dropping funnel, and a reflux condenser was added 1 1. of anhydrous ether and 12 g. (0.317 moles) of lithium aluminum hydride. A solution of 30 g. (0.178 moles) of l-naphthoic acid in 650 ml. of anhydrous ether was added to the stir- red suspension over a period of two hours. After addition was complete, the mixture was refluxed for six hours. The reaction mixture was then cooled in an ice bath, hydrolyzed with water (2 m1./g. of hydride), and the precipitated alkoxides dissolved by adding 5% sulfuric acid. The aqueous layer was separated and extracted with several portions of ether. The ether extracts were combined, washed with 10% sodium bicar— bonate, dried over anhydrous magnesium sulfate, filtered, and the ether was evaporated. Recrystallization of the crude alcohol three times from a mixture of benzene and cyclohexane gave 23 g. (88%) of d-naphthyl- carbinol, m.p. 60.5-61.5° (lit. 59.5-6l°). B. Preparation of a-Naphthylcarbinol-a,a-d;. 1-Naphthoic acid was reduced by the previous procedure with lithium aluminum deuteride. C. Preparation of d-Naphthylcarbinol-8-d. 1-Naphthoic acid-8-d was reduced by the previous procedure with lithium aluminum hydride. D. Preparation of a-Naphthylcarbinyl proluenesulfonate. This compound was prepared by the method of Kochi and Hammond (61). 68 69 To a 200 m1., three-necked, round bottom flask equipped with a Tru- bore stirrer, reflux condenser, and a dropping funnel was added 35 m1. of anhydrous ether, 2 g. (0.013 moles) of a-naphthylcarbinol, and 0.31 g. (0.013 moles) of sodium hydride. After the mixture had been stirred and refluxed for twelve hours, it was cooled with a dry ice-acetone bath to —20° and a solution of 2.81 g. (0.013 moles) of purified.p-tolu- enesulfonyl chloride dissolved in 35 to 80 ml. of anhydrous ether was added dropwise to the suspension. After addition was complete, the re- action mixture was stirred for two hours at -10° and then at room temper- ature for an additional hour. In all operations care was taken to ex- clude moist air from the system. The reaction mixture.was then filtered repeatedly with a minimum exposure to the air, using a medium grade sintered glass funnel until a clear suspension was obtained. The clear solution was then cooled in a dry ice-acetone bath until a copious precipitate of fine white needles was obtained. These crystals were collected on a Bflchner funnel and stored in a stoppered Erlenmeyer flask. Attempted recrystallization from 2,8-dimethylpentane (b.p. 79.80) re- sulted in decomposition. Recrystallization from pentane produced a white crystalline compound decomposing at 55—56°. Due to the compound's insolubility some decomposition occurred during recrystallization. Therefore, the material was recrystallized by adding it to 300 ml. of boiling pentane and adding anhydrous ether until solution was complete. The recovered material decomposed at 55.50. E. Preparation of d-Naphthylcarbinyl pritrobenzoate. Five grams (0.032 moles) of d-naphthylcarbinol, 5.9 g. (0.032 moles) of p-nitro- benzoyl chloride, 3.0 g. (0.038 moles) of pyridine, and 800 m1. of 70 anhydrous ether were added to a 2 1., single-necked,round bottom flask fitted with a reflux condenser. The reaction mixture was refluxed for twenty-four hours, 600—800 ml. of ether was then added, and the mixture was poured into a beaker containing 5% hydrochloric acid and ice. The aqueous and ether layers were separated and the ether layer washed with 10% soidum bicarbonate, distilled water, dried over anhydrous magnesium sulfate, filtered and the ether was evaporated. Recrystallization of the crude product three times from a 8:1 cyclohexane-benzene mixture gave 5 g. (53%) of a-naphthylcarbinyl p—nitrobenzoate, m.p. 126-127°. F. Preparation of a-Naphthylcarbinyl 3,5—Dinitrobenzoate. Five grams (0.032 moles) of a-naphthylcarbinol, 7.3 g. (0.032 moles) of freshly prepared 3,5-dinitrobenzoyl chloride, and 2.5 g. (0.032 moles) of pyridine were added to a 2 1., single-necked, round bottom flask containing 900sz of anhydrous ether and fitted with a reflux condenser. The reaction mixture was allowed to stand at room temperature for twenty—four hours. The precipitate was collected on a Buchner funnel and repeatedly extracted with a boiling 8:1 mixture of cyclohexane- benzene until no further precipitate dissolved. The boiling extracts were filtered, cooled, and the crude product collected on a Bachner ' funnel. ,M—Heptane was added to the original ether solution which was then cooled in a dry ice-acetone bath, and the precipitate was collected. Recrystallization of the combined products three times from a 8:1 cyclohexane-benzene mixture gave 6.5 g. (58%) of d-naphthylcarbinyl 3 ,5-dinitrobenzoate, m.p . 162 . 5—163 , 5,0 71 G. Prgparation of l—Bromonaphthalene-8-d. Previous to use all glassware was thoroughly cleaned in sulfuric acid, liberally rinsed with distilled water, and oven-dried. A 500 m1., three—necked, round bottom flask was fitted with a Tru- bore stirrer, a pressure equilibrated dropping funnel containing an outlet tube, and a reflux condenser. A second 500 m1., three-necked, round bottom flask containing a ground glass stopper and an inlet tube was joined to the first flask by a u-tube fitted to the top of its re- flux condenser. With dry argon passing, the entire system was flamed out. In all subsequent operations dry argon was passed through the system. After cooling, ether and lithium aluminum hydride were added to the second flask and approximately 200 ml. of dry ether was distilled over into the reaction vessel. With the argon flow increased, 1.82 g. (0.075 moleS) of high purity magnesium which had been oven-dried and cooled in a desiccator, 25 g. (0.076 moles) of 8-iodo—l-bromonaphthalene, and several drops of ethylene dibromide were added to the reaction vessel. The flow of argon was reduced and reversed, and the ether sus- pension warmed to initiate the reaction. A gentle rate of reaction was maintained for two hours, after which time the mixture was refluxed for an additional two hours. The reaction mixture was then cooled in an ice bath and 10 ml. of deuterium oxide was added dropwise from the dropping funnel. After addition was complete, the mixture was stirred for an additional thirty minutes. The ice bath was then removed and stirring was continued for eight hours at room temperature. With the argon flow discontinued and a calcium chloride drying tube inserted into the t0p of the condenser, the reaction mixture was stirred overnight.. 72 The ether layer was then separated and the aqueous phase was extracted with two 100 m1. portions of ether. The combined ether portions were washed, dried over anhydrous magnesium sulfate, filtered, and the ether was evaporated. Two successive preparations were combined and vacuum distilled; b.p. 82-88° at 0.5 mm. and llO-ll2° at l to 2 mm. Percent- age yields varied from 70 to 83%. H. Preparation of l—Naphthoic Acid-8-d. -The basic procedure used was that of Gilman and co-workers (62). The same type of apparatus as described in the preparation of l-bromonaphthalene—8-d was used. The following describes the steps involved in a typical preparation. Approximately 250 m1. of dny ether was distilled into the reaction vessel containing 2.95 g. (0.121 moles) of dry purified magnesium. Using a pipet 50 ml. of the ether was quickly withdrawn and added to 28.65 g. (0.118 moles) of l-bromonaphthalene-B-d. The resulting solution was added to the dropping funnel. Several drops of ethylene dibromide and a small aliquot of the l-bromonaphthalene-B-d solution was added to the reaction vessel which was then placed in a warm.water bath to initiate the reaction. Stirring was then commenced and the remaining l-bromonaphthalene-8-d solution was added at such a rate as to maintain a vigorous but not violent reaction. After addition of the l-bromonaphthalene-B-d solution was complete, the reaction mix- ture was refluxed for one hour. Dry benzene, 50 ml., was added to dissolve the Grignard reagent and the reaction vessel was immersed in a dry ice-acetone bath. The temperature was.adjusted to -7 to -10°, argon—flow was discontinued, and the dropping funnel was replaced by an entry tube, 10 mm. in diameter, which was adjusted so that its end was 73 about 50 mm. above the surface of the reaction mixture. The temperature was measured by suspending a thermometer through the condenser which was fitted with a calcium chloride drying tube. The reaction mixture was stirred and dry carbon dioxide was admitted through the entny tube. The rate of carbon dioxide flow was controlled so that the temperature did not rise above -2°. When the reaction temperature started to fall the flow of carbon dioxide was increased and maintained for about thirty minutes. The reaction flask was then placed in an ice bath and 25% sulfuric acid was slowly added with stirring until reaction had ceased and all excess magnesium had dissolved. The oily layer was separated and the aqueous layer was extracted with two 50 ml. portions of ether. These were combined with the original ether-benzene fraction, and the resulting solution was filtered if it was not clear. The com- bined ether—benzene fractions were then extracted with three 35 m1. por- tions of 25% sodium hydroxide. Each alkaline layer was successively ex- tracted with a 25 m1. portion of ether and the combined alkaline extracts were heated to 90° to drive off the volatile components. The solution was then cooled and strongly acidified with 50% sulfuric acid. The crude l—naphthoic acid-8-d was collected on a Bachner funnel, washed free of sulfate, and dried. Recrystallization from 3:1 heptane-tolu- ene yielded 18 g. (81%) of 1-naphthoic acid-8—d, m.p. 163-163.5°. (Lit. 160°) I. Prepgration of a-Naphthylcarbinyl Chloride. Five grams (0.032 moles) of a-naphthylcarbinol was added to a 50 m1., round bottom flask fitted with a reflux condenser. Six grams (0.050 moles) of thionyl chloride was slowly added from the top of the condenser and the mixture 78 was refluxed for approximately one hour. The reaction mixture was then transferred to a 10 m1. flask, the excess thionyl chloride stripped off, and the crude a-naphthylcarbinyl chloride vacuum distilled. The dis- tilled chloride was then recrystallized from purified petroleum ether (b.p. 80-60°) and stored under dry petroleum ether (m.p. 31-31.5°). J. Preparation of a-Naphthylcarbinyl Chloride-8-d. d-Naphthyl- carbinyl chloride-8-d was prepared by the procedure described for a-naphthylcarbinyl chloride. K. Preparation of a-Nappthylcarbinyl Chloride a,a-d2. a-Naphthyl- carbinyl chloride-0,0-d2 was prepared by the procedure described for d-naphthylcarbinyl chloride. L. Preparation of 8—Bromo-a-Naphthylcarbinyl Chloride. 8-Bromo- d-naphthylcarbinyl chloride was prepared by the procedure described for d-naphthylcarbinyl chloride. M. Prepgration of 8—Methyl-a-Naphthylcarbinyl Chloride. 8-Methy1- a-naphthylcarbinyl chloride was prepared by the procedure described for a-naphthylcarbinyl chloride except that several drops of pyridine were added to the reaction mixture after refluxing for forty—five minutes. II. Product Studies A. Methanolysis of a-Naphthylcarbinyl pritrobenzoate. To a 100 nut,single necked, round bottom flask fitted with a reflux condenser and a calcium chloride drying tube was added 1 g. (3.25 x 10'3 moles) of c-naphthylcarbinyl p-nitrobenzoate and 75 ml. of purified anhydrous 75 methanol. After refluxing for one week the methanol was removed by a Rinco rotary evaporator and the precipitate placed under vacuum for one hour to remove any traces of methanol. The crude material was dis- solved in 6 ml. of carbon tetrachloride and 3 ml. was chromatographed on 25 g. of alumina using carbon tetrachloride, benzene, and ether as eluting solvents. The carbon tetrachloride elutable material yielded methyl pfnitrobenzoate, identified by its infrared spectrum and m.p. The benzeneikaction.yielded essentially no material. The ether elutable material yielded a-naphthylcarbinol, identified by its infrared spectrum and m.p. No a-naphthylcarbinyl methyl ether was recovered. The yield of a—naphthylcarbinol was over 100% based on one-half of the solvolysis mixture. B. Methanpgysis of a-Naphthylcarbigyl 3,5-Dinitrobenzoate. To a 100 m1., single necked, round bottom flask fitted with a reflux condenser and a calcium chloride drying tube was added 1 g. (2.83 x 10-3 moles) of d-naphthylcarbinyl 3,5-dinitrobenzoate and 75 ml. of purified anhy- drous methanol. After refluxing the reaction mixture for one week, the ester had not completely dissolved. Therefore, an additional 25 m1. of methanol was added and the mixture was refluxed for an additional five days. After cooling the reaction mixture was filtered to remove the small amount of precipitate, presumably unsolvolyzed ester, and the methanol was removed using a Rinco rotary evaporator. The crude product was placed under vacuum for one hour to remove any traces of methanol. The crude product was dissolved in 6 m1. of carbon tetrachloride and 3 ml. was chromatographed on 25 g. of alumina using petroleum ether (b.p. 80-60°), carbon tetrachloride, cyclohexane, benzene, ether, and 76 ethylene dichloride as eluting solvents. The petroleum ether, carbon tetrachloride, and cyclohexane fractions yielded no material. The benzene fraction contained a trace of material tentatively identified as d-naphthylcarbinol by its infrared spectrum. The ether elutable material was shown to be d-naphthylcarbinol by infrared spectra and m.p. No a—naphthylcarbinyl methyl ether, 3,5—dinitrobenzoic acid or methyl 3,5-dinitrobenzoate was recovered from the column. Within ex- perimental error the yield of recovered alcohol was quantitative. C. Insoluble Products Formed During_§olvolysis of a-Naphthylcarb- inyl Chloride in Aqueous Formic Acid. a-Naphthylcarbinyl chloride (8.926 9., 0.0279 moles) was dissolved in 2 l. of 97-100% formic acid. After standing for eighty-four hours at room temperature, the solution was filtered and the precipitate collected on a Bflchner funnel. The precipitate was dissolved in boiling ether, filtered, and repeatedly washed with saturated sodium bicarbonate. The aqueous washings were re-extracted with ether and the combined ether fractions were washed with a small portion of saturated sodium.bicarbonate, water, dried over anhydrous magnesium sulfate, and filtered. The aqueous fraction, after acidification with nitric acid, gave a negative chloride test with silver nitrate. A small portion of the ether solution was evaporated to dryness. The nuclear magnetic resonance spectrum (CC14) shows absorption peaks at 1r = 5.2, 8.8, and 3.3 to 1.8 with relative areas roughly 1:6:28. The infrared spectrum (082) shows bands at 3050-3100 cm.'1, 2950 cm.'1, 1720 cm.'1, 1600 cm.-1, 1800 cm.'1, and 1160 cm,-1. 77 A small portion of the ether solution was evaporated to dryness and dissolved in acetone. Addition of aqueous silver nitrate produced a white precipitate indicating formation of silver chloride. The re- sulting suspension was repeatedly filtered until a clear solution was obtained. Water was then added and the resulting suspension extracted with several portions of ether. The ether fractions were combined, washed, and dried over anhydrous magnesium sulfate. The nuclear magnetic resonance spectrum (0014) shows absorption peaks at ‘r = 5.2, 8.8, and 3.3 to 1.7. The infrared spectrum (cs2) shows bands at 3500 cm.“1 1 1 (weak), 3000 cm.‘ , 1720 cm.‘1, 1100 cm." , 1020 cm ' It had been previously shown that under the same conditions a-naphthylcarbinyl chloride is converted to d-naphthylcarbinol. The remaining ether solution was evaporated to dryness and the crude mixture chromatographed on silica gel. Carbon tetrachloride ; 5:1, 1:1 and 1:3 mixtures of carbon tetrachloride-benzene, benzene, 1:1 mixture of benzene-ether, ether, and methanol were used as eluting sol- vents. Thin layer chromatography, using a 1:1 mixture of carbon tetra- chloride and benzene as the eluting solvent, was utilized to determine the extent of separation and the number of products. The appropriate fractions were then combined for infrared and nuclear magnetic reso- nance Spectra. The principal absorptions of the various fractions are given in Table XXVI. Only a trace material was obtained in the methanol fraction. D. Insoluble Products Formed Durng Solvolysis of 8-Metgyl-o- Naphthylcarbinyl Chloride in Aqueous Formic Acid- The precipitate. formed during solubility studies of 8-methyl-a-naphthylcarbinyl chloride 78 was collected on a Bachner funnel, dissolved in ether, washed repeatedly with saturated sodium bicarbonate, water, dried over anhydrous magnesium sulfate, and filtered. After evaporation of the ether, nuclear magnetic resonance and infrared spectra were obtained. Table XXVI. Infrared and nuclear magnetic resonance spectral data of fractions from chromatographic studies of the insoluble products from the solvolysis of a-naphthylcarbinyl chloride. Fraction I.R.(cm.‘1) N.M.R. (1~) 1- 9 3050, 2950, 1700-1950, 5.2, 5.1, 1600, 1520, 1850, 1830, 3.17-1.7 1800, 1280, 1285, 1100, 1030 10-11 3100, 2950, 1720, 1600, 5.3, 8.5, 1520, 1870, 1850, 1830, 3.3-1.7 1800, 1160 12 ---- 5.3, 8.5, 303-107 13-18 3100, 2950, 2850, 1720 5.3, 5.1, 1690, 1600, 1520, 1870, 3.3-1.7 1800, 1260, 1160 19 ---- 5 1, 3 3-1 7 20-21 3000, 1720, 1690, 1600, 5.2, 1520, 1870, 1800, 1170 3.3-1.7 III. Analytic Procedures A. Preparation of Reagents and Standard Solutions Purification of Carbon Tetrachloride. was purified by the method given by Vogel (63). phosphorus pentoxide. Carbon tetrachloride It was distilled from 79 Purification of Petroleum Ether. Petroleum ether was purified by the method given by Vogel (63) except that it was dried over magnes- ium sulfate and distilled from calcium hydride. The fraction boiling in the range 37-57° at atmospheric pressure was collected. Preparation of 1 M Potassium Chloride. Oven-dried "Baker Analyzed" reagent grade potassium chloride, 18.6390 9., was quantita- tively transferred to a 250 m1. volumetric flask and diluted to the mark with distilled water. Prepgration of Potassium Thiocyanate. Solutions were prepared by taking the approximate quantity of potassium thiocyanate and diluting in a given volumetric flask. These solutions were stored in brown stoppered bottles. Preparation of Silver Nitrate Solutions. Silver nitrate solu- tions of approximate molarities were prepared by adding the approximate quantity of silver nitrate to a volumetric flask. After diluting, these solutions were stored in brown bottles. Preparation of Indicator Solutions. Ferric nitrate indicator solutions, O.33 M and 2 M, were prepared from Baker and Adamson reagent grade ferric nitrate by adding the approximate amount of reagent to the approximate volume of water. Preparation of Primagy Standard Sodium Chloride Solutions. Primary standard sodium chloride solutions were prepared from "Baker Analyzed" reagent grade sodium chloride by the usual procedures (29). 80 During potentiometric titration these solutions were prepared with temperature equilibrated water. Solutions less than 10'3 M were prepared from the appropriate ali- quots of stock solution and the appropriate calibrated National Bureau of Standards volumetric flasks. Preparation of Primary Standard Silver Nitrate Solutions. Primary standard silver nitrate solutions were prepared from "Baker and Adamson" reagent grade silver nitrate by the usual method. For potentiometric titration of solutions less than 10-3 M in chloride standard solutions were prepared by using National Bureau of Standards calibrated volumetric flasks. Preparation of Sodium Chloride Solutions in Formic Acid. Matheson formic acid (97-100%) exhibited a negative chloride test and was used without further purification. Solutions were prepared from the appropriate quantities of oven—dried "Baker Analyzed" reagent grade sodium chloride. Preparation of Solutions of Hydrogen Chloride in Formic Acid. Matheson formic acid (97-100%) was used without further purification. Dry hydrogen chloride (Matheson) waslubbled directly into approximately. 2 l. of formic acid contained in a clean dry 2 l. Erlenmeyer flask. Periodically samples were withdrawn and the chloride concentration determined by Volhard titration. When the chloride concentration ap- proximately reached 0.1 M, it was accuratedly determined and the solu- tion stored in a ground glassstoppered flask. 81 Dilute solutions were prepared by buretting volumes of this stock solution into clean,dry 100 m1. volumetric flasks and diluting to the mark with formic acid. General Techniqees. Accurate weighings were performed using Mettler balances. Distilled water was used in all analytical procedures. Silver nitrate and potassium thiocyanate solutions were stored in l l. brown bottles. Each bottle was fitted by means of 28/80 ground glass joints with a liquid outlet and air inlet tube. Using clean tygon tubing the outlet was connected to the bottom of the automatic filling micro—buret and the inlet to a rubber squeeze bulb. The tubing and exposed glass fitting were wrapped with black tape. When not in use, the solution was protected against the atmosphere by closing the tubing with pinch clamps. B. Calibration of Glassware. Pipets and volumetric flasks were calibrated by established methods (30). Weighings were performed using a Mettler balance except for 500 ml. and l l. volumetric flasks, which were weighed to the nearest 0.01 g. on a large free swinging balance. Correction factors were obtained from Blaedel and Meloche (29). The micro—burets were not calibrated. Kimax National Bureau of Standards calibrated 1 l. and 2 l. volumetric flasks were also used. C. Volhard Titrations. Procedure 1. Macroscopic samples were analyzed by the usual procedure (29). 82 Procedure 2. The basic procedure using micro—burets was adapted from Blaedel and Meloche (29) and Kolthoff and Sandell (30). A given aliquot of sodium chloride solution was delivered to a 300 ml. Erlenmeyer flask; 5 ml. of 1:1 concentrated nitric acid-water solution (boiled for several minutes) was added, and a measured excess of silver nitrate was added while the solution was magnetically stirred. The excess volume of silver nitrate was kept as small as possible. Nitrobenzene (3-3.5 ml.) was then added, the flask stoppered with a clean rubber stopper and vigorously Shaken until a clear point was ob- tained. Indicator (2 ml. of 0.33 M Fe(N03)3) was added and the excess silver ion back-titrated with potassium thiocyanate. Silver nitrate solution was standardized by titration against primary standard sodium chloride solutions. Potassium thiocyanate was standardized against silver nitrate by the procedure described above. Procedure 3. This procedure was modified from that of Swift e£.,elo- (31). Seven to eight milliliters of a 1:1 mixture of concen- trated nitric acid and water, 1 ml. of_nitrobenzene and, depending upon the total titrating volume, 2 or 8 m1. of 2 M indicator were used. Samples were diluted with 35 to 80 ml. of water. D. Potentiometric Titration. Apparatus. The indicator electrode was a Beckmann (No. 30788) silver billet electrode that dipped into the titration beaker. A salt bridge connected the titration beaker to a small jacketed flask con- taining 1 M potassium chloride and a Beckmann (No. 39170) saturated 83 calomel electrode. The reference half cell was connected to a constant temperature bath maintained at 23.00 i 0.05°, although such thermostat- ting is not necessary unless determinations of concentrations less than 10-3 M are being made. The titration beaker was surrounded by a black cloth bag to keep out light, and its contents were stirred rapidly dur- ing titration with a magnetic stirrer. The potential between the silver and calomel electrodes was measured with a Leeds and Northrup Type K potentiometer and a PYE Scalamp galvanometer. During titration galvo- nometer sensitivity was switched to the x1 position. An Eppley standard cell (serial number 768083) was used. Power was supplied from four 1.5 volt dry cell batteries producing 6 volts. Preparation of Silver Electrode. The silver electrode was soaked in a 1:1 solution of concentrated nitric acid and water, to which a little sodium nitrite had been added, until the surface was bright. It was then rinsed liberally with distilled water and polished with a fine grade of emeby cloth. For continued stability the electrode was polished from time to time or whenever the surface became darkened. Preparation of Salt Bridge_. The salt bridge was a Ueshaped glass tube 10 mm. in diameter, 15 cm. high, and 12 cm. wide. It was inverted and filled with a hot liquid 3% solution of agar-agar in 1 M potassium nitrate. After cooling to room temperature this solution formed a thick gel and solidified. Care was taken to exclude air bub- bles and to ensure that the solidified gel completely filled the tube. A number of these salt bridges were prepared at the same time and stored in a desiccator with their ends immersed in l M potassium nitrate. 88 The 3% agar—agar in l M potassium nitrate was prepared by the fol- lowing method. 0ven-dried Baker reagent grade potassium nitrate (50.5538 g.) was weighed into a tared 50 ml. beaker and quantitatively transferred to an uncalibrated 500 ml. volumetric flask. A 200 ml. aliquot of this solution was pipetted into a clean 300 ml. Erlenmeyer flask and 6.000 g. of agar-agar was added. The suspension was then placed into a beaker of boiling water and heating continued until the solution became clear. General Titration Procedures: (a) Solutions.greater than 10-3 M in chloride: A given volume of halide solution was delivered into a 150 ml. beaker containing approximately 75 ml. water and an appropriate volume of formic acid. The entire titration beaker was covered with a black cloth bag and the sample titrated by adding ali- quots of silver nitrate, rinsing the buret tip, and reading the corres- ponding potential. Silver nitrate solutions not prepared as primary standard reagents were standardized by titration against primary standard sodium chloride. (b) Solutions less than 10-3 M in chloride: A given volume of halide solution was delivered into a 150 ml. beaker containing a given amount of formic acid and enough water to bring the final volume to 100 i 5 ml. The entire titration beaker was covered with a black cloth bag. Standard silver nitrate solution was delivered into the beaker from a 10 m1. microburet, graduated in 0.02 ml. intervals, while the solution was efficiently stirred. Initially, the potentiometer was set about 15 mv. less than the previously determined equivalence point potential and silver nitrate delivered until a null reading on the 85 galvanometer was obtained. The titration was then stopped, the external balance of the potentiometer was checked, and the potentiometer was set at the determined equivalence point potential. Silver nitrate was then added slowly until a null reading on the galvanometer was obtained. IV. Extraction Procedures A. Procedure 1. A 10 m1. aliquot of hydrogen chloride in formic acid was delivered to a 125 ml. separatory funnel containing 50 ml. of carbon tetrachloride and 20 m1. of distilled water. The mixture was then extracted, the carbon tetrachloride layer run into a second separa- tory funnel containing 15 ml. of distilled water, and the extraction repeated. The extractions were standardized at 80 and 30 shakes, respectively. The water layers were then quantitatively transferred to a 300 ml. Erlenmeyer flask and the chloride content determined by Volhard titration. B. Procedure 2. To a 125 ml. separatory funnel containing 50 m1. of carbon tetrachloride and 25 ml. of distilled water was pipetted a given volume of solution, allowing 15 seconds drainage time. The mix- ture was-then vigorously extracted, the carbon tetrachloride layer run into a second separatory funnel containing 15 ml. of distilled water and the extraction repeated. The extractions were standardized at 50 and 30 shakes, respectively. Each aqueous phase was then extracted with a small portion of purified petroleum ether and then quantitatively transferred to a 150 ml. beaker. The chloride content was then deter— mined by potentiometric titration. For aqueous sodium chloride solutions either a 5 or 10 m1. aliquot of formic acid was added. 86 V. Determination of Appearance of Turbidity in the Solvolysis of d-Naphthylcarbinyl Chloride as a Function of Concentration Formic acid freshly distilled from boric anhydride was used with- out determination of its water content. Assuming 0% water in the formic acid, 0.83 M and 0.28 M solvents were prepared by adding a given weight of water to the appropriate volumetric flask and dilut- ing to the mark with formic acid. Assuming 0.15% water in the formic acid, 0'25.E solvent was prepared by adding a given weight of water to a weighed quantity of formic acid. various molar concentrations of a-naphthylcarbinyl chloride were prepared in each solvent. An appropriate amount of compound was weighed into a glass st0ppered Erlenmeyer flask and a given volume of solvent added. The flask was then stoppered, shaken until solution was complete and allowed to stand at room temperature. Periodically the flasks were examined for the appearance of turbidity. VI. Preparation of Aqueous Formic Acid-—Solvent for Kinetic Runs A. Purification of Formic Acid. The method used.was that of Winstein and Marshall (68). To a 5 1. round bottom flask which was fitted with a 20 inch frac— tionating column and a distillation head was added 8 1. (approximately 8800 g.) of Matheson 97-100% formic acid. The low boiling components were distilled off and heating continued until the head temperature reached 99°. The formic acid was allowed to cool and 775 g. of boric anhydride was added. -This amount of boric anhydride was calculated assuming the water content of the formic acid to be 8%. Four grams of 87 boric anhydride was used per gram of calculated water. After standing for 3 days the formic acid was decanted into a clean dry 5 1. round bottom flask, and 150 g. of fresh boric anhydride was added. The frac- tion boiling in the range 27 to 33° at 50 i 10 mm. was collected, trans- ferred to a brown bottle, and stored at 5°. B. Determination of the Water Content in Formic Acid. The small water content of the formic acid purified by the above procedure was determined by Karl Fischer titration using the two solution technique (65). The small water content of the blank was determined by titrating 25.00 ml. of the methanol solution which had been buretted into a clean, dry 125 ml. Erlenmeyer flask. A weighed amount of water was then added and titrated. A clean, dry, stoppered 125 ml. Erlenmeyer flask was weighed. A sample of formic acid to be titrated was introduced from a clean, dry pipet, the flask stoppered, and re-weighed. The stoppered flask and its contents were placed in an ice bath and 25.00 m1. of the methanol solvent added. The resulting solution was then titrated. In calculating the water content of the formic acid, the volume of reagent required to titrate the blank was subtracted from the total reagent volume. Results were reproducible to i 0.02%. C. Preparation of 0.32QMMWater in Formic Acid. A clean, dry 2 l. volumetric flask was weighed to the nearest 0.01 g. The anhydrous formic acid was transferred to the volumetric flask. From the results of the Karl Fischer titration, the amount of additional water required to prepare a 0.32 M solution was calculated and added from a weight buret. The solution was thoroughly mixed, transferred to a clean, dry brown bottle, and stored in a cold room when not being used. 88 VII. Rate Determination An amount of compound was accurately weighed into either a 100 ml. or 200 ml. volumetric flask. Temperature equilibrated solvent was then added to about 80% capacity. The volumetric flask was then stoppered and vigorously shaken until solution of the material was complete. The solution was then dfluted to the mark, the flaSkinverted several times to effect complete mixing, and the contents transferred to a clean, dry polyethylene squeeze bottle from which 5.5 ml. or 10.5 ml. ampoules were filled. Initial time of mixing was called zero time. At definite time intervals an ampoule was withdrawn, broken open, and a 5 ml. or 10 ml. aliquot withdrawn. The reaction was quenched by extracting the sample using extraction procedure 2. Time was recorded at the end of the first extraction. The average sampling time was approximately 2 minutes i 10 sec. The volume of the resulting solution was adjusted to 100 m1. and its chloride content determined by potentiometric titration. For 5 ml. aliquots an additional 5 ml. of 97% formic acid was pipetted into the beaker before titration. During kinetic studies on 8-methyl-a-naphthylcarbinyl chloride and 8-bromo—d-naphthylcarbinyl chloride, the sealed ampoule technique was not used. During kinetic studies on 8-methyl—a—naphthylcarbinyl chloride the second extraction was not performed until the end of the run. In most cases the average of three samples was.taken for the infinity titre. Bath temperature was 25.008 i < 0.01°. PART II SOME PROTON—13C COUPLING CONSTANTS IN SUBSTITUTED ARYLCARBINYL COMPOUNDS 89 PART II INTRODUCTION It is generally agreed that the major contribution to the short range proton-13C coupling, is the Fermi contact term (66). J13C—H’ The elucidation of factors affecting long range proton 13C coup- ling has been less extensively investigated. Karabatsos and co-workers (67) were able to conclude that the contact term dominates J13C-C—H when 13C-C—H angle is tetrahedral. However, three bond coupling showed no simple dependence on the contact term. Karabatsos and Orzech (68) have postulated, from studies of 13C labeled neo—pentyl derivatives, that spin-dipole and electron-orbital effects contribute to both J13C-H and J13C-C—C-H since no simple re- lationship between electronegativities and coupling was observed. Furthermore, some of the variations of J13C-C-C-H could only be qual- itatively explained by assuming bond bending as a result of steric re- pulsions (69). Qualitatively, the magnitude of J should decrease as the bond is bent, since the overlap is being reduced. The availability of a number of l,8-disubstituted naphthalene derivatives suggested themselves as systems to test these effects on the magnitude of J13C-H' The values of J13C_H were obtained for the isomeric halo and methyl toluenes and benzyrl alcohols. RESULTS Summarized in Tables XXVII, XXVIII, and XXIX are the J13C-H for the various naphthalene compounds, isomeric toluenes, and isomeric benzyl halides, respectively. The coupling constants were obtained from 13C natural abundance. Table XXVII. Proton-13C couplings calculated from substituted naphtha— lenes. Compound J13C_H(CH3) J13C_H(CHZ) Solvent B-methylnaphthalene 125.5 CC14 a-methylnaphthalene 126.0 neat 8-bromo—l-methylnaphthalene 127.2 CCl4 8-methy1-d-naphthylcarbinol 125.2 182.0 acetonea 8-bromo-d-naphthylcarbinol 188.0 acetonea d-naphthylcarbinol 181.0 ,_ acetone a5% HCl added. 91 92 Table XXVIII. Proton-13C couplings calculated from isomeric toluenes. Compound J13C-H (CH3) Solvent parent 125.5 neat e-F 127.1 neat 3-01 127 .0 neat e—Br 127.0 neat e—I 126.8 neat e-Me 125.0 neat M-F 126.0 neat M-Cl 126.0 neat M—Br 126.0 neat M—I 125.8 neat M-Me 125.0 neat p-F 125.6 neat p—Cl 125.6 neat p—Br 125.7 neat p—I 125 .6 cm4 125.7 neat 93 Table XXIX. Proton-13C couplings calculated from isomeric benzyl alcohols. Compound J13C_H (CH2) JISC-H (CH3) Solvent parent 181.0 neata e—F 183.8 neata e-Cl 182.5 acetone e-Br 182.5 acetonea e—Me 180.8 125.5 neat M-P 182.1 neata M-01 181.8 nea ta M-Br 181.3 neat .E‘I 181.8b neata M-Me 181.8 125.8b neat er 181.8 neata p—Cl 181. 5 cc14 p-Br 180.8 acetone p—I 181.3b neat p—Me 180.7 125.8 0014 p-MeO 180.6 neat a5% H'Cl added. bIncreased uncertainty. DISCUSSION Examination of the results reveahsthat differences in JlsC—H are very small. For halotoluenes (Table XXVIII) differences within the ortho, meta, and para isomers are negligible. Small differences exist between the ortho, meta, and para positions. These differences are in quali- tative agreement with expectations based on the influence of electro- negativity on JISC-H' The order J13C_H(p) < J13C—H(m) < J13C_H(o) is in agreement with the increasing inductive effect. That only insig- nificant differences are observed within each series must mean that only gross electronegativity effects are important and that small elec- tronegativity differences among the halogens produce changes of no greater than several hundredths of a cps. in J13C-H' Whether the rela- tive increase observed for the ortho halogens is due entirely to the increased inductive effect or also represents contributions from spin- dipole and electron-orbital terms is difficult to assess. .The some- what anomalous behavior of iodine is well documented and reflected by its dr'and cr+ values (70). Table XXIX reveals that the same trends in J13C-H are observed for the benzyl alcohols. Due to the increased uncertainty of J13C—H values, the small differences within each positional isomer must be treated with scepticism. Table XXVII reveals that the largest changes in J13C_H are ob- served for 8-bromo-a-methylnaphthalene and 8-bromord—naphthylcarbin01. The differences for the remaining naphthalene compounds are small. 98 95 Steric strain is probably present in the 1,8-disubstituted compounds. This strain is probably relieved by in-plane splaying-out of the Ca-Cg-C9 and Ca—Cl-Cg bonds and also possibly by bending the groups out of the naphthalene plane. Comparison of the coupling constant of 8-methyl-d-naphthylcarbin01 with those of 0- and 8-methyl naphthalene and d-naphthylcarbinol reveals that the effect of these steric inter- actions on J13C-H is probably small. Previously it has been postulated that part of the slow rate of solvolysis of 8—bromo—d-naphthylcarbinyl chloride was due to the enhanced inductive effect because of the close proximity of the bromine. The increase observed in the J13C—H in the 8-bromo compounds is in agreement with this hypothesis. However, part of the observed increase may be due to contributions from spin- dipole and/0r electron-orbital terms. EXPERIMENTAL A. Substituted Bengyl Alcohgie. Commercially available benzyl alcohol and pfmethoxybenzyl alcohol were used without further purifica- tion. The remaining alcohols were prepared by reduction of the corres- ponding acids with lithium aluminum hydride. e—Fluoro- and M—fluorobenzyl alcohols were prepared by lithium aluminum hydride reduction of the corresponding aldehydes. B. Substituted Toluenes. Commercially available compounds were used without purification. The N.M.R. spectra were in accord with the structures. C. Substituted Naphthalenes. Either commercially available compounds or compounds previously prepared were used. All N.M.R. spectra were determined at 60 Mo. on a Model A-60 spectrometer (Varian Associates, Palo Alto, Calif.L at a temperature of about 36°. The coupling constants, determined at sweep width of 250 cps., are the averages of at least three determinations with an estimated precision of i 0.2 cps. 96 (1) (2) (3) (8) (5) (6) (7) (8) (9) (10) (11) (12) (l3) (l8) . (15)' (16) (17) BIBLIOGRAPHY Lewis, E. S. and C. E. Boozer, J. Am. Chem. Soc., 1M, 6306 (1952). Shiner, v. J., Jr., ibid., 15, 2925 (1953). For a recent review see E. A. Halevi in "Progress in Physical Organic Chemistry," Vol. 1, edited by S. G. Cohen, A. Streitwieser, Jr. and R. W. Taft, New York: Interscience, 1963. a) Shiner, v. J. ,Jr. J. Am. Chem. Soc. 78, 5285 (1952); b) Lewis, E. S. Tetrahedron, 5, 183 (1959)— a) Shiner, v. J., Jr., J. Am. Chem. Soc. ,76, 1603 (1958); b) Shiner, V. J., Jr. and 8. Cross, ibid. ,79, 3599 (1957). Shiner, V. J., Jr. and G. S. Kriz, Jr., ibid., 8Q, 2683 (1968). a) Shiner, V. J., Jr., ibid., lg, 2653 (1956); b) ibid., 83, 280 (1961). Shiner, V. J., Jr. 2813 (1963). Shiner, V. J., Jr. and J. S. Humphrey, Jr., ibid., 8M, 2816 (1963). B. L. Murr, and G. Heinemann, ibid., 82: S Shiner, v. J., Jr. and J. 0. Jewett, ibid., MM, 985 (1968). For a discussion, see "Indiana University Conference on Hyper- conjugation," V. J. Shiner, Jr. and E. Campaigne, co-chairmen, Tetrahedron, g, 105-278 (1959). Dewar, M. J. S., "Hyperconjugation," New York: Ronald Press Co., 1962. Streitwieser, A., Jr., R. H. Jagow, R. C. Fahey, and S. Suzuki, J. Am. Chem. Soc., 89, 2326 (1958). a) Bartell, L. S. J. Chem. Phys, 32, 827 (1960); b) Tetra— hedron,l7, 177 (1962); c) Tetrahedron Letters, No. 6, 13 (1960); 'd) J. Am. Chem.. Soc. ,83, 3567 (1961). Melander, L. and R. E. Carter, ibid., Me, 295 (1968). Ha) Mislow, K., R. Graeve, A. J. Gordon, and G. H. Wahl, Jr., ibid., M5, 1199 (1963); b) ibid., MM, 1733 (1968). Raaen, V. F., T. K. Dunham, D. D. Thompson, and C. J. Collins, 97 (18) (19) (20) (21) (22) (23) (28) (25) (26) (27) (28) (29) (30) (31) (32) (33) (38) (35) 98 Ferguson, 0. and J. M. Robertson in "Advances in Physical Organic Chemistry," Vol. 1 edited by V. Gold, New York: Academic Press, 1963. 3 Donaldson, D. M. and J. M. Robertson, J. Chem. Soc., 17 (1953). For leading references see H. C. Brown and I. Moritani, J. Am. Chem. Soc., 77 3623 (1955); b) Brown, H. C., J. Chem. Soc., 1288 (1956);-C) Science 292, 385 (1986) and references cited therein. Banthorpe, D. V., E. D. Hughes, and C. K. Ingold, J. Chem. Soc., 8058 (1960) and references cited therein. Moritani, I. 3820 (1959)- Nishida, S., ibid., Me, 8290 (1960). S. Nishida, and M. Murakami, J. Am. Chem. Soc., 8;, 3 Winstein, S. and N. J. Holness, ibid., 11, 5562 (1955). a) Brown, H. C., and K. Ichikawa, Tetrahedron, l, 221 (1957); b) Brown, H. C., 0. H. Wheeler, and K. Ichikawa, ibid., M, 218 (1957); c) Brown, H. C. and K. Ichikawa, J. Am. Chem. Soc., ég, 373 (1962)‘ Shone, R. L., Ph.D. thesis, Michigan State University, 1968. Jacobs, T. L. and S. Singer, J. Org. Chem., 875 (1952). Nakanishi, K., "Practical Infrared Absorption Spectroscopy," San Francisco: Holden Day, Inc., 1962, p. 22. Blaedel, W. J. and V. W. Meloche, "Elementary Quantitative Analysis," White Plains, N.Y.: Row, Peterson, and Co., 1957. Kolthoff, I. M. and E. B. Sandell, "Textbook of Quantitative Inorganic Analysis," New York: MacMillan Co., 3rd edition, 1952. Swift, E. H., G. M. Arcand, R. Lutwack, and D. J. Meies, Anal. Chem., Mg, 306 (1950). Fainberg, A. H. and S. Winstein, J. Am. Chem. Soc., 18, 2770 (1956). (Bateman, L. c. and E. D. Hughes, J. Chem. Soc., 1187 (1937). Shiner, V. J., Jr. and M. L. Smith, Anal. Chem., 28, 1083 (1956). Kolthoff, I. M. and H. H. Furman, "Potentiometric Titrations," New York: John Wiley and Sons, 1926. 99 (36) Meires, L. and H. C. Thomas, "Advanced Analytical Chemistry," New York: MCGraw—Hill Book Co., Inc., 1958, Chapter 3. (37) Armstrong, 0. w., H. H. 0111, and R. F. Rolf in "Treatise on Analytical Chemistry," edited by I. M. Kolthoff, P. S. Elving, and E. B. Sandell, Part II, Vol. 7, New York: Interscience, 1961, pp. 368-377. (38) a) Shiner, V. J., Jr. and J. W. Wilson, J. Am. Chem. Soc., 8M, 2802 (1962); b) Shiner, V. J., Jr., 0. Heinemann, J. W. Wilson, and N. Solliday, ibid., 88, 2808 (1962). (39) Streitwieser, A., Jr., "Solvolytic Displacement Reactions," New York: MCGraw-Hill Book Co., Inc., 1962. (80) Swain, C. G. and W. P. Langsdorf, Jr., J. Am. Chem. Soc., 13, 2813 (1951)- (81) Bensley, B. and G. Kohnstam, J. Chem. Soc., 8787 (1957). (82) a) Dewar, M. J. S. and R. J. Sampson, ibid., 2789 (1956); b) ibid., 2986 (1957). (83) Handbook of Chemistry and Physics, 39th edition, Cleveland, Ohio: Chemical Rubber Publishing Co., 1957, pp. 1869-1870. (88) Fierens, P. J. C., H. Hannaert, J. Van Rysselberge, and R. H. Martin, Helv. Chim. Acta., 33M, 2009 (1955). (85) Benson, S. W., "The Foundations of Chemical Kinetics," New York: MCGraw-Hill Book Co., Inc., 1960, p. 86. (86) Streitwieser, A., Jr., "Molecular Orbital Theory for Organic Chemists," New York: John Wiley and Sons, Inc., 1961, p. 105. (87) Sevast'yenov, N. G., G. S. Zhdanov, and M. M. Umanski from B. M. Webster in "Progress in Stereochemistry," edited by W. Klyne and P. B. D. de la Mare, Vol. 2, New York: Academic Press, 1958. (88) Trotter, J., Can. J. Chem., 32, 1578, 1968 (1961). (89) Trotter, J., Acta. Cryst., 23, 732 (1960). (50) Hall, D. M., S. Ridgewell, and E. E. Turner, J. Chem. Soc., 2898 (1958). (51) Grubb, E. L. and C. P. Smyth, J. Am. Chem“ Soc., 83, 8873 (1961). (52) Harrison, A. G., P. Kebarle, and F. P. Lossing, ibid., 83, 777 (1961). (53) Brown, H. C. and Y. Okamoto, ibid., 89, 8979 (1958). (58) (55) (56) (57) (58) (59) (60) (61) (62) (63) (68) (65) (66) (67) (68) (69) (70) 100 Mason, S. F., J. Chem. Soc., 808 (1958). Dewar, M. J. S. and R. J. Sampson, ibid., 2952 (1957). Okamoto, Y. and H. C. Brown, J. Am. Chem. Soc., 22, 1903 (1957). a) Brown, H. C. J. D. Brady, M. Grayson, and W. H. Bonner, ibid. 79,1897 (1957); b) Brown, H. C, Y. Okamoto, and G. Ham, ibid. 79,1906 (1957); c) Okamoto, Y. and H. C. Brown, ibid. ,79, 81909 (1957); d) Brown, H. C., Y. Okamoto, and T. Inukai, ibid. 8968 (1958); e) Brown, H. c. and T. Inukai, ibid.,83_—8825_(1961). Baddeley, C. (1958). Chapman, N. B. J. Chadwick, and H. T. Taylor, J. Chem. Soc., 2805 3 , J. Shorter, and J. H. P. Utley, 1919': 1291 (1963). Verbit, L. and E. Berliner, J. Am. Chem, Soc., 8Q, 3307 (1968). Kochi, J. K. and G. S. Hammond, 1919': ZE, 3883 (1953). Organic Syntheses, collective vol. II, p. 825. Vogel, A. 1., "Textbook of Practical Organic Chemistry," London: Spottis Woode, Ballantyne and Co., Ltd., 3rd edition, 1961. Winstein, S. and H. Marshall, J. Am. Chem,.Soc., 2M, 1120 (1952). Stone, K. 0., "Determination of Organic Compounds," New York: MCGraw-Hill Book Co., Inc., 1956, Chapter 1. a) Shoolery, J. N. ,J. Chem. Phys, 31, 1827 (1959); b) Muller, C. N. and D. E. Pritchard, ibid. ,31,768, 1871 (1959); C) Gutowsky, H. S. and C. S. Juan, ibid. ,88, 307 (1962). Karabatsos, G. J., J. D. Graham, and F. M. Vane, J. Phys. Chem., M5, 1657 (1961). Karabatsos, G. J. and C. E. Orzech, Jr., in press. Karabatsos, G. J. and C. E. Orzech, Jr., private communication. Leffler, J. E. and E. Grunwald, "Rates and Equilibria of Organic Reactions," New York: John Wiley and Sons, Inc., 1963. APPENDIX 101 late APPENDIX Data Obtained from the Solvolysis Rate Measurements The following tables contain the data obtained from the rate measure- w = weight (g.) of arylcarbinyl chloride. V = corrected volume (m1.) of the volumetric flask used in each run. A0 = the initial concentration of arylcarbinyl chloride. M AgNOs = the molarity of silver nitrate used in a run. Pip.V01.= the calibrated volume (m1.) of each pipet. Titre = volume of standard silver nitrate required to titrate chloride in an extracted kinetic sample. [X] = the concentration of chloride at time t. t = time in minutes. Xeq.av. =the average value of the chloride content at equilibrium, M. k = rate constant obtained by least squares analysis. The molecular weights of the arylcarbinyl chlorides used to calcu- Ao were: a-naphthylcarbinyl chloride = 176.53 a—naphthylcarbinyl chloride—B—d = 177.58 a-naphthylcarbinyl chloride-a,a—d2 = 178.58 8-bromo-a-naphthylcarbinyl chloride = 255.88 8—methyl-a-naphthylcarbinyl chloride = 190.58 102 103 Table XXX. Solvolysis 0f a-naphthylcarbinyl chloride in 0.32 m water- formic acid. Run 1. w = 0.3163 9.; v = 199.88 m1.; A0 = 8 968 x 10‘3 M. Pip. V01. Titre M AgNOs x 103 [X] x 103 t (min.) (m1.) (m1.) - 10.03 2.282 5.076 1.155 51.31 9.996 8.800 2.238 108.51 10.01 6.575 3.338 178.23 9.997 8.030 8.077 233.96 9.998 9.235 8.689 291.63 9.982 10.28 5.207 387.93 10 00 6.870 9.086 5.853 882.53 9.991 6.985 6.328 583.28 9.988 7.380 6.688 685.00 9.990 8.030 7.271 equilibrium 9.990 8.010 7.253 equilibrium 9.990 8.030 7.271 equilibrium _ -3, _ -5 -1 Xeq.av. — 7.265 x 10 , k - 8.63 x 10 sec. . Table XXXI. Solvolysis of a-naphthylcarbinyl chloride in 0.32 m water- formic acid. Run 2. w = 0.3039 9.; v = 199.88 m1.; A0 - 8.613 x_10'3 y t (min.) Pip. V01. Titre 13.1191103 x 103 [x] x 103 (m1.) (m1.) 10.03 2.130 5.076 1.078 51.79 9.996 8.302 2.188 110.80 10.01 6.338 3.218 180.65 9.997 7.880 8.001 282.36 9.998 9.125 8.633 301.32 9.982 10.25 5.212 367.79 10 00 10.99 5.579 828.93 9.991 6.878 9 086 6.227 561.86 9.989 7.182 6.508 667.91 10.02 7.800 6.681 777.88 9.999 7.870 7.120 equilibrium 9.999 7.862 7.113 equilibrium 9.999 7.850 7.102 equilibrium - X eq.av. = 7.112 x 10‘3; k = 8.55 x 10‘5 sec.’1. 108 Table XXXII. Solvolysis of a-naphthylcarbinyl chloride in 0.32 m water- formic acid. Run 3. w = 0.3075 9.; v = 199.80 ml.; A0 = 8.718 x 10‘3 M- Pip. v61. Titre M 891703 x 103 [x] x 103 t (min.) (m1.) (m1.) " 10.03 2.575 5.076 1.303 58.77 9.996 8.785 2.830 121.02 10 01 6.958 3.528 193.82 9.997 8.390 8.260 256.81 9 998 9.575 8.861 317.10 9.982 10.78 5.882 381.92 10.00 6.580 9.086 5.952 886.06 9.991 6.910 6.256 589.91 9.988 7.275 6.589 666.82 9.993 7.810 6.708 781.52 9.990 7.895 7.189 equilibrium 9.990 7.930 7.181 equilibrium 9.990 7.905 7.158 equilibrium xeq.av.= 7 163 x 10‘3; k = 8.62 x 10'5 sec.'1. Table XXXIII. Solvolysis of a-naphthylcarbinyl chloride in 0.32 m water-formic acid. Run 8. w = 0.3025 9.; v = 199.88 m1.;.Ao = 8.573 x 10‘3 y. 4‘ Pip. V01. Titre M AgNO3 x 103 [x] x 103 t (min.) (m1.) (m1.) 4— - 10.03 2.365 5.053 1.191 57.37 9.996 8.800 2.228 116.66 10.01 6.290 3.175 181.13 9.997 8.000 8.088V. 258.55 9.998 9.125 8.612 316.88 9.982 10.10 5.113 376.01 10.00 5.800 10.06 5.832 888.02 9.991 6.080 6.082 573.88 9.988 6.388 6.398 673.16 9.993 6.885 6.528 750.98 9.989 6.899 6.988 equilibrium 9.989 6.865 6.918 equilibrium 9.989 6.870 6.919 equilibrium X eq.av. = 6.927 x 10‘3; k = 8.57 x 10'5 sec.'1. 105 Table XXXIV. Solvolysis of a-naphthylcarbinyl ch10ride—8-d in 0.32 m water-formic acid. Run 5. w = 0.3038 9.; v = 199.88 m1.; A0 . 8 561 x 10'3 g. Pip. V01. Titre M AgN03 x 103 [X] x 103 t (min.) (m1.) (m1.) - 10.03 2.630 5 053 1.325 61.63 9.996 8.880 2.288 116.80 10.01 6.280 3.170 179.76 9 997 7.695 3.889 239.65 9 998 8.995 8.586 302.89 9.982 9.960 5.082 365.15 10.00 5.560 10.06 5.593 852.78 9.991 6.080 6.122 588.15 9.988 6.382 6.828 686.57 9.993 6.890 6.533 753-62 9.989 6.885 6.938 equilibrium 9.989 6.910 6.959 equilibrium 9.989 6.905 6.958 equilibrium Xeq.av. = 6.989 x 10 3; k = 8.58 x 10 5 sec. 1. Table XXXV. Solvolysis 0f d-naphthylcarbinyl chloride-8-d in 0.32 m water-formic acid. Run 6. w = 0.3231 9.; v = 199.88 m1.; A0 = 9.105 x.10'3 y. Pip. v61. Titre M A91103 x 103 [x] x 103 t (min.) (m1.) (m1.) ‘ . «- ‘-' 10.03 2.680 5 053 1.350 57.10 9 996 8.825 2.839 116.83 10 01 6.760 3.812 179.61 9.997 8.225 8.157 237.01 9.998 9.882 8.792 297.05 9 982 10.56 5.386 357.77 10.00 11.82 5.770 820.85 9.991 6.162 10 06 6.208 503.01 9.988 6.570 6.617 613.09 9.993 6.795 6.880 737.68 9.989 7.285 7.296 equilibrium 9.989 7.228 7.279 equilibrium 9.989 7.280 7.291 equilibrium 9.989 7.285 7.296 equilibrium ‘ X eq.av. = 7,290 x 10-3; k = 8.53 x 10"5 sec. ‘1 106 Table XXXVI. Solvolysis 0f d-naphthylcarbinyl ch10ride-8-d in 0.32 m water-formic acid. Run 7. w = 0.1638 9.; v = 99.865 ml.; A0 = 9.215 x 10‘3 M. Pip. v61. Titre M 1191703 x 103 [x] x 103 t (min.) (m1.) (m1.) - 10 03 3.005 5.053 1.518 65.15 9.996 5.590 2.826 138.79 10.01 8.080 8.059 230.05 10.00 10.10 5.108 325.62 9.998 5.800 10.11 5.865 826.50 . 9.989 18.73 5 053 7.851 equilibrium 9.989 18.78 7.856 equilibrium _ -3, _ -5 -1 xeq av. - 7.853 x 10 , k - 8.85 x 10 sec. . Table XXXVI. Solvoysis of a-naphthylcarbinyl chloride in 0.32 m water- formic acid. Run 8. w = 0.1658 9.; v = 99.865 ml.; A0 . 9.382 x 10’3 M Pip. v61. Titre .8 11191103 x 103 [X] x 103 t (min.) (m1.) (m1.) - ‘ -‘-‘ 10.03 2.665 5 053 1.383 60.13 9.990 8.982 2.500 120.32 9.993 6.820 3.888. 180.87 9.982 8.862 8-288 282.86 10.00 9.925 5.015 310.87 8.986 5.505 5.579 380.23 8.992 5.902 5.978. 859.86 8.986 6.550 6.638 608.58 8.992 6.882 6.926 718.88 3.985 5.820 7.380 equilibrium 8.986 7.310 7.808 equilibrium 8.986 7.385 ‘7.888 equilibrium , X eq.av. = 7.811 x 10‘3; k = 8.80 x 10.5 sec.-1. 107 Table XXXVIII. Solvolysis of a-naphthylcarbinyl chloride-0,0-d2 in .O.32 m water—formic acid. Run 9. w = 0.1750 9.; v = 99.865 ml.; A0 - 9 815 x 10‘3 M Pip. v61. Titre M 891103 x 103 [x] x 103 t (min.) (m1.) (m1.) — 9.991 2.100 5.053 1.062 60.33 9.988 8.007 2.027 120.56 9.998 5.660 2.856 180.90 10.02 7.265 3.668 286.07 10 03 8.285 2.159 312.63 8.986 5.380 5.812 889.86 8.992 6.178 6.253 593.00 8.986 6.670 6.760 782.38 8.992 7.630 7.723 equilibrium 8.992 7.680 7.778 equilibrium 8.992 7.670 7.768 equilibrium _ -3. _ -5 -1 Xeq.av. - 7.758 x 10 , k — 3.31 X 10 sec. . Table XXXIX. Solvolysis of a-naphthylcarbinyl chloride-0,0-d2 in 0.32 m water-formic acid. Run 10. w = 0.1853 9.; Va 99.857 ml.; A0 = 1.039 x,10‘2 M. Pip. v61. Titre M A91103 x 103 [x] x 103 . t (min.) (m1.) (m1.) " » 9.991 2.250 5.053 1.138 60.09 9.988 8.290 2.170 121.26 9.996 6.022 3 088 182.08 10.01 7.560 3.816 281.88 9.989 8.998 8.552 303.86 8.986 5.070 5.139 371.63 8.992 5.665 5.738 838.25 8.986 6.812 6.898 576.63 8.986 6.862 6.958 706.89 8.986 7.920 8.026 equilibrium 8.988 7.990 8.097 equilibrium 3.985 6.320 8.018 equilibrium X = 8.086 x 10'3; k = 3.29 x 10‘5 sec.'1. eq.av. 108 Table XL. Solvolysis of d—naphthylcarbinyl chloride-0,0-d2 in 0.32 M water—formic acid. Run 11. w = 0.1778 9., v = 99.865 ml.; A0 = 9.972 x 10‘3 M. Pip. v61. Titre M 11191103 x 103 [x] x 103 t (min.) (m1.) (m1.) 10.02 2.225 5 053 1.122 59.95 9.998 8.085 2.065 120.11 9 982 5.755 2.913 180.19 10.00 7.285 3.661 281.38 9.993 8.610 8.358 306.95 8.986 8.880 8.905 375.17 8 986 5.395 5.868 887.11 8 988 6.200 6.286 589.82 8.988 6.780 6.833 736.85 8 986 7.655 7.758 equilibrium 3.985 6.080 7.709 equilibrium 3.985 6.060 7.688 equilibrium _ -3. _ -5 -l Xeq.av. - 7.717 x 10 , k - 3.35 x 10 sec. . Table XLI. Solvolysis of a-naphthylcarbinyl chloride in 0.32 M water- formic acid. Run 12. w = 0.1695 9.; v = 99.865 ml.; A0 . 9.615 x 10"3 M. Pip. v61. Titre M 1191103 x 103 [x] x 103 - t (min.) (m1.) (m1.) , ~~ » -‘ 9.996 2.882 5.053 1.857 61.82 9 998 5.335 2.696 125.17 10 00 7.180 3.608 188.55 10.01 8.880 8.883 251.86 8.988 5.165 5.236 325.97 8.986 5.782 5.819 801.87 '8.988 6.210 6.296 876.35 8.986 6.710 6.800 605.73 8.988 7.505 7.609 equilibrium 8.988 7.860 7.563 equilibrium 8.988 7.890 7.598. equilibrium 9.989 15.09 7.633 equilibrium X = 7.600 x 10‘3; k = 8.35 x 10‘5 sec.'1. eq.av. 109 Table XLII. Solvolysis 0f d-naphthylcarbinyl chloride in 0.32 m water— formic acid. Run 13. w = 0.1757 9.; v = 199.80 ml.; A0 = 8.981 x 10’3 M. Pip. v61. Titre .8 1191103 x 103 [x] x 103 t (min.) (m1.) (m1.) 9 998 1.535 5.053 0.7758 68.82 9.996 2.818 1.828 126.90 10.01 8.630 2.337 289.68 9.982 5.882 2.775 323.91 10.02 6.320 3.187 808.70 9 988 7.022 3.552 511.66 9 990 7.765 3.928 665.87 9 989 8.865 8.888 equilibriuma 9.989 8.875 8 889 equilibriuma 9.989 8.885 8.895 equilibrium: 9.989 9.000 8.553 equilibriumb 9.989 9.015 8.560 equilibriumb 9.989 9.020 8.563 equilibrium a _ ‘3 . _ -5 -1 eq.av. - 8.889 x 10 at 27.5 hours, k - 8.83 x 10 sec. . .. ‘3 . g -5 -1 eq.av. - 8.559 x 10 at 51-52 hours, k 8.32 x 10 sec. . Table XLIII. Solvolysis 0f 8~brom0-a-naphthylcarbinyl chloride in 0.32 M water—formic acid. Run 18. w = 0.1333 9.; v = 99 865 ml.; A0 = 5.225 x 10‘3 M. Pip. v61. Titre M 11191103 x 103 [x] x 103 t (min.) (m1.) (m1.) _' - ‘ " 9.998 1.090 5.053 0.5509 28.99 9 998 1.220 0.6166 28.18 9 998 1.380 0.6772 31.90 9.998 1.680 0.8289 80.81 9 998 2.320 1.173 63.85 9.998 8.080 2.082 129.82 9.998 6.020 3.083 235.55 9 991 9.680 8.896 equilibrium 9.991 9.650 8.880 equilibrium . x = 8.888 x 10‘3; k = 6.15 x 10‘5 sec.'1. 110 Table XLIV. Solvolysis of 8-bromo-a-naphthy1carbinyl chloride in 0.32 M water-formic acid. Run 15. w = 0.1281 9.; v = 99.857 ml.;.Ao = 5.022 x 10 318 Pip. V01. Titre M 119103 x 103 [x] x 103 t (min.) (m1.) (m1.) 9.996 1.680 5.053 0.8892 87.96 9.996 2.795 1.813 87.80 9 996 3.862 1.952 132.78 9.989 5.150 2.605 198.98 9.988 6.520 3.299 295.07 10.01 7.260 3.665 368.88 9.990 8.065 8.079 891.18 9.982 9.360 8.738 equilibrium 9.982 9.350 8.733 equilibrium _ '3. - ’5 -1 Xeq.av. — 8.736 x 10 , k - 6.11 x 10 sec. . Table XLV. Solvolysis of 8-methyl-a-naphthylcarbinyl chloride in 0.32 M water-formic acid. Run 16. w = 0.0987 9.; v = 100 ml.; A0 = 5.18 x 10'3‘M. Pip. v61. Titre M 119103 x 103 [x] x 103 t (min.) (m1.) (m1.) . ‘ - ' * 9.991 9.030 5.053 8.567 8.90 9.982 9.50C) 8.809 16.12b 9.993 9.580 8.825 19.89 9.990 9.565 8.838 equilibrium 9 996 9.585 8 825 equilibrium 9 996 9.565 8.835 equilibrium X eq.av. = 8.831 x 10'3; k = 3.8 x 10-3 sec. -1 aRate constant obtained from estimation of half-life treating data as simple FIRST ORDER REACTION. bTaken as infinity titre.