HEGH FREQUE CY T§?M?EGN OF SGL‘éE MGNGBASSC A59?) WEASSC A5233 3% NOR-AQUEWS MEDRA Thai: for fho Dogma of M. S. MICHIGAN STATE UNWERSRTY Lawrenco La Roy Fleck 1958 LIBRARY Michigan State University HIGH FREQUERCY TITRATION OP SOL‘EE MCI-EOBASIC AND DIBASIC ACIDS IN ROE-AQUEOUS KLEIA BY Len-once Laney Fleck Submitted to the College of Science and Arts of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of RA STISR OF SC I MTCE 'Department of Chemistry 1958 AC KN OJJIEEG-MEZNTS The euthor ie deeply indebted to Dr. Andree Timnick for hie guidance and hie help given throughout the entire inveetigetion and preparation of thie mCII. e Acknoeledgment ie eleo extended to . Er. Dente A. Conetenzo for hie helpful euggeetione in the oonetruction or the high frequency titration epparetue. fl iii-#19112 iii-{8341' ii VITA Heme: Lawrence LeRoy Fleck Born: February 24, 1931 in Kalemezoo. fiichigan St. Augustine High School, Kalemezoo, Acedemic Cereer: iicbigan (1945—1949) Western Kichigen College, Kelemeeoo, Kichig en (19 51-19 55) fiichigen State University, East Leneing, Elohigen (1955- ) Degreee Held: AB. 3. Western Eichigan College (1955) 111 HIGH FREQUENCY TITRATION OF SOME MONOBASIC AND DIBASIC ACIDS IN NON-AQUEOUS MEDIA 3! Lawrence LeRoy Fleck AN ABSTRACT Submitted to the College of Science end Arts of Hichigen State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SC IENCE Department of Chemistry Year 1958 Approved W A {13 '33 AC '1’ A eteble high frequency titration epperntue wee eonetructed. Thie instrument, utilising e plete type cepecitence cell, was employed for all high frequency titretione conducted in this investigation. ihe high frequency titration resulte obtained in thin investigation eere evaluated by comparing these reeulte with those obtained by conductimetric end potentiometric methods. The ehepe of the high frequency and conductimetric titration curvee eere eimiler for’ell eoide titrated. Tetrobutylommoniun hgdroxide wee tested on e titrant for the high frequency titration of come monobaeic and dibeeic acids diesolved in non-aqueous colvente. The beet over-e11 titration rcaulte were obtcincd for acid: dieeolved in 60% benzene-20S methanol. chcr solvents examined were dimcthyl forwamide, methyl isobutyl ketone, Bofi'bennene-lofi methanol. and so; benzene-fioj'methanol. The high frequency titration: of benzoic and eelioylic ecid dieeolved inmemhyl isobutyl ketone were uneuoceeeful due to poorly defined titration and points. Phenol, however. eee eucaeeefully titrated in methyl ieobutyl ketone eith tetrebutylemmonium hydroxide. The following monobeeic end polybeeic ecide dieeolved in 80% benzene-20% methanol were successfully titrated V with tetrabutylemmonium hydroxide: adipic, bencoic, citric. fumaric, maleic, malonic, oxalic, salicylic, eebacic, and auccinic acids and vanillin. Tuo end points in the titration curves, corresponding to the neutralization of both carboxyl groups, were obtained for the dibaeic ecide. The second titration end point for these acids was sharper than the first. Citric acid, a tricarboxylic acid, gave two good and pointe. The third end point for citric acid was poorly defined. The titration of fumaric and maleic acid mixturea dieaolved in 80% benzene-20% methanol with tetrahutyl- ammonium hydroxide resulted in four distinct and points. The mean percentage purity value for the total acid content was found to be 96.3 i 2.5% for four trials. vi TABLE OF COETENTS INfiiODUCTICNOOOOO0.0.00....0..ODOOOOOOOOOOOOOOOOOOOO ’iISTORICAL BACKGROUHDOOOOOOOIOOCOIOOOOOOO0.0...0.... Ron‘.qu00u. Q‘itPIMCtYYeeeeeeeeeeeeeeeeeeeeeeeeege Eon-aqueoue High Frequency Titrimetry............ EXPERIMERTALDeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee R..g.nt.eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee APP‘PIWIeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee Titration PPOOOdur03eeeeeeeeeeeeeeeeeeeeeeeeeeeee Fotentiometric Titretione........"nun...“ Conductimctrio Titrationl...u.Human"... High FPOQUODOy Titration.......o"no...o..." r‘ISCE'SSION OF RESULTSOOCO0.0IOOOOOOCCOOOOOOOOOOOOOOO Inetrument Response Curvee....................... High Frequency and Conductimetric Titretione..... nonobaaic Acids in Retnyl Isobutyl Ketone..... fionODOSIO ACidfl 1n Benzene-335613113110]...o........ Polybasic Acids in Benzene-Methanol........... Potentiomotrio Titratimfloeeeeeeeeeeeeeeeeeeeeeee Comparison of Titration Results.................. Titration of 301‘! fugixcurefleeeeeeeeeeeeeeeeeeeeee. SUB-1*:ARY AED COEJCLITSI‘QLIOCIOOO.OOOOOOOOOOOOOOOOOOOOOOO LITLRATLRE CITEDeoeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee. vii LIST OF TABLES TABLE Page I Titration. of Monobeeic Acid. with TCtr3bUtyI-‘mmonim Hydroud.e e e e ee e e ee e e e ee e e ee 29 II Titreticne or Polybaeic Acid: uith Totrabutylemmonium Hydroxide. e e e e e ee 0 e e e co e e e e e 31 III High P’requency Titration Result: for Fumeric 36 and ”31.10 Aflid antmleeeeeeeeeeeeeeeeeeeeeee viii LI ST OF FIGURES FIGURE 1’ '8' Schematic Diagram of fiodified fligh Frequency 1. Titration ApparItUIeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 14 2. High.Frequency end Conductimctric Response Curvee for Tetrabutylammonium,fiydroxide.......... 19 3. High Frequency Titratione of Benzoic Acid in Several Beneene-Eethenol Mixed Sclvcnte.......... 22 4. High Frequency Titration Curves for Salicylic Acid end Some Dicerboxylic Acids in Benzene- u.th‘n°10eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 24 6. High Frequency end Potentiometric Titretione cf Citric Acid in Benzene-methanol, Tetrebutyl- ”112110211113 Hydroxide Titl'.nteeeeeeeeeeeeeeeeeeeeeee 25 6. Potentiomctric Titration of Melonic Acid in Benzene-methanol and Adipic Acid in Hethyl Ieobutyl Ketcne, ictrebutylemmonium Hydroxide Tltl‘mteeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 27 7. High Frequency Titration of Fumaric Acid end Heleic Acid mixtures in Benzene-Kethcnol, ?ctrabutyammonium Hydroxide Titrant.............. 35 ix INTRODUCEIGE Jensen and Parrack (34), who pioneered high frequency titratione in the United States, greatly enlarged the scope or high frequency titrimetry by conducting titrations in non-aqueous media. High frequency titrations conducted in non-aqueous solvante offer several advantages over those conducted in aqueous solutions. The main advantages are: 1) non- equeoue solvents can be chosen which increase the apparent acidity or baaicity of teak acids or bases dissolved in them and, 2) these solvents dissolve many organic acids or bases which are not ordinarily soluble in water. The choice of titrant depends on the characteristics of the solvent, the apparent acidity or basicity of the material being titrated, and the strength of the titrant. These are the main factors that are considered when choosing a suitable titrant-solvent system for non- equeous high frequency titrinctry. Several investigators (7,11,12,25,25,25) hflVB shown that tetrabutylammonium hydroxide in non-aqueous solvents is a good basic titrant for potentiomctric titration and differentiation of strong, seek, and very soaks acids in non-aqueous media. These workers used tetrsbutylammonium hydroxide successfully as a titrsnt for acids dissolved in a variety of solvents including methyl isobutyl ketone, dimethyl formsnide, cthylsnediamine, lxl benzene- isopropyl alcohol, benzene-methanol, acetonitrile, pyridine and others. Wyld, 215;. (23) foxmd that tetrabutylantnonium hydroxide dissolved in isopropyl alcohol compared favor» ably in performance with alcoholic potassium hydroxide for the potentiometrie titration of phenol in several non-aqueous solvents. In vies of this work a study eas undertaken to test the performance of tetrabutylammonium hydroxide as the titrant for non-aqueous high frequency titretions or some monobasic and dibasic acids. cihroughout this thesis acids similar in strength to mineral acids are designated as "strong acids , those similar in strength to unsubstituted csrboxylic acids are designated as "weak acids", and those similar in strength to phenol are designated as ”very seek acids”. HISTORICAL BACKGROUND Several reviews (18.20.54.61) of fundamental developments in non-aqueous analysis have appeared in the recent literature. Skolik (58) reviewed the roles of solvents and standard solutions, the determinations of endpoints, applications and sources of errors in non- aquecus titrimetry. Higuchi, 3.5.31... (28) discussed the results of spectrophotometric and potentiometric studies mo 13 indicators in anhydrous acetic acids Van der Heine and Dahmen (60) determined an empirical acidity potential scale of 12 solvents by potentiometric titrations of strong acids aith strong bases. Eilpatrick (41) dis- cussed the theoretical and practical problems of acidity measurements in non-aqueous media. flooser (51) included a brief review of nonoaqueous titrations and listed a complete bibliography of non-aqueous high frequency titrations reported through 1954. The {aliasing extensive revise is for the period from 1954 through the November 10, l957 issue of Chemical Abstractg. Non-agneousgitrimetrz Perchloric acid in glacial acetic acid has been used extensively for potentiomctric titrations (4,9,15,16,17, 30,39,40,45.47) and for photometric titrations (17,28) of a large variety of organic bacea diacolvad in glacial acetic acid. Titration of some organic bacec using dioxane (29,53), acetonitrilc, and nitromcthanc (9). and chloroform (10} aa aolvonte have been performed poten- 'tiomatrically with a atendard.perchlcrio acid solution. Blake (5) back titrated a measured exceca or perchlorio acid in glacial acetic acid with sodium acetate for the Tao ditterant typos determination or come organic baaea. of electrode ayatema (53.5?) were characterized by neutralization titrationa with parchlcric acid. Kolthofr (42) interpreted acid-baae titrationa in glacial Palit and Singh (51) investigatcd phenol acetic acid. aa a coaolvont with glycola for organic bases tibratcd with atandard pcrchloric acid. Eiaukami and Eirni (50) titrated 5-acotamidoaethy1- 4-amino-9-mcthylpyrimidino in glacial acetic acid with atandard periodic acid using a mdxcd indicator composed of methyl violet and bromophcnol blue. Bumerouc titrationa of acida dissolved in dimcthyl formamide (4,14,45) benzene-methanol (3,4,4?) ethylene- diamdne (14) or pyridina with sodium methoxide have been performed. Strculi (59) titrated heterocyclic amino cult: of polymora diaaolvod in dimothyl formamide with 1,5-di-o- tolylguanidino in 139 methanol-chloroform. Chatton (8) titrated Eraminooalioylic acid and ita aodium aalt with alcoholic potassium hydroxide in methanol using acetone as the non-aqueous medium. Deal and Wyld (12) used alcoholic potsenium.hydroxide as a basic titrent for the titration of very weak acids using ethylenediemine and dimethyl formamide as solvents. Martin (48) titrated peracids, hydrogcn peroxide and hydroperoxides as weak ecids in anhydrous ethylene- diamine with sodium aminoethoxide using antimony electrodes in a potentiometric titration procedure. Kcrchmer (3?) determined mercaptane in the presence of elemental sulfur by titration with an alcoholic silver nitrate solution. two types of solvents were employed in this study. One, a "regular" solvent, contained sodium acetate trihydrate in a small amount or water, benzene and isopropyl alcohol, and the other, an I'aciclic" solvent contained sodium acetate trihydrste, glacial acetic acid, methanol and bensene. Brummet and Hollweg (6) demonstrated the applica- bility of using chelating agents in non-aqueous titrimetry. They determined the concentrations of several metal ions in bensene-methsnol by adding a cheleting agent and titrating the liberated hydrogen ions with sodium nethoxide. wyld,‘g§.gl, (24) compared the performance of polarised pletinumpcelomel electrodes with glass-calomel electrodes in titretions in which potassium hydroxide or sodium aminoethoxide in ieopropyl alcohol was the titrent. Henry, _e_§ 2;. (£7) titrated organic bases conduc- tinstricslly with boron tribromide in aprotic solvents. Several recent articles {7.11.12.19.23.25.2e) reported the titrations of acids using tetraalkylammoniun hydroxides as the basic titrants. dyld and Bruce (7) found that methyl isccutyl ketone see a good differ- entiating solvent for the titration of acids. Non-agueous High Freguencl Titrimetr; hooser (31) compared high frequency titration results with corresponding conductimetric and poten- tiometric titratione. He successfully titrated esak acids dissolved in dimethyl formnmide or bensene-nethanol sith alcoholic potassium hydroxide. Excellent results sere reported for high frequency titrations of some very seek acids such as‘g—hydroxydiphcnyl,phenol, pybromov phenol, Q-nephthol and for week diccrboxylic acids such as edipic acid. Only one endpoint was reported in the titration of the dicsrboxylic acids. Hell, 33,3}. (21) successfully titrated boric acid in methanol in the presence of glycerol with sodium hydroxide in methanol. Iehidate and Masui (32) titrated some salts of organic acids with perchloric acid or sodium acetate in acetic acid. Dean and Gain (13) titrated salicylic acid, potassium.acid phthalete, beneoic acid, gynitrOphenol, boric acid, ammonium bromide and ammonium iodide in diasthyl formamide with sodium methoxide. They also reported that gybutylamine was a suitable non-aqueous titrant for ”stronger acids”. Lane (43) determined the equivalent weights of a large number or organic bases dissolved in glacial acetic acid eith perchloric acid. Lone (dd) also reported the determination of mercury (11) by the precipitation of copper dipropylenediamine mercuric iodide. The precip- itate was dissolved in glacial acetic acid and mercuric acetate and titrated with perchloric acid in glacial acetic acid. In the cane report Lane also describes the determinations of some metal ions by chelation and subsequent titration of the liberated hydrogen ions with a standard solution of potassium methoxidc. Young (62) titrated lithium halides and other salts with a standard solution of silver nitrate in a pyridine solution. he also reported that high frequency methods can be used to determine alkali metal acetates by titra- tion with perchloric acid. Lippincott and Timnick (as) determined aniline, substituted anilines, and mixtures of substituted anilines in glacial acetic acid with a standard perchloric acid titrant. Karrman and Johaneson (38) used potassium methoxidc in 10:1 benaene-methanol for the titration of nonohydroxy-, dihydroxy-and trihydroxy phenols dissolved in benzene- methanol or benzene-dimcthyl formemide. They also reported that when mixtures of phenols were titrated, each component gave a titration break in the order of decreasing dissociation conatant. 81010 and Maroon (55) reported that titrations of dihydrOphenazine with potassium diohronate in glacial acetic acid gave sharp high frequency endpoints. They also titrated organic bases dissolved in glacial acetic acid with a standard pcrchloric acid solution (56). Allen and co-workers (1) employed a Q-Meter for non- aqueous titration of sulfonamidcs and the sodium and potassium salts of organic acids. Hera and test (22) successfully titrated a number of organic acids, bases, and chelating grours in non- aqueous solvents. Titrationa of lactic, tartaric, succinic, citric, formic, or propionic acids dissolved in pyridine with alcoholic potassium hydroxide were carried out. The bases dissolved in glacial acetic acid were titrated with pcrchloric acid. EXPERIMENTAL Reagents The chemicals used in this investigation were not repuriried unless otherwise noted. Repurification of the organic acids was not considered necessary, since the high frequency titrations were evaluated by comparing these results with those obtained by conductimetric and potentiometric titrations. The compounds titrated, labeled purity, and source are 8 Organic Acids: Adipic acid Citric acid Fumaric acid Haleic acid Malonic acid Oxalic acid Phenol Salicylic acid Sebacic acid Succinic acid Vanillin Recrystallised from acetic‘acid Fisher, Certified Reagent Practical Eastman, practical Dow Company Reagent grads Eastman White Label Colemmn and Bell, C.P. Eastman, Practical Baker's Analysed Reagent Retort Pharmaceutical, U.S.P. Other chemicals used were: Primary Standards: Bensoic acid dried over sulfuric acid Potassium acid phthalate ovendried.for tso Other Chemicals: hours at 105° Amberlite I.R.A.-4OO resin analyticalgrade Tetrabutylammonium iodide fiatheson, Coleman and Bell or Eastman Kodak 10 Solvents: Benzene,“ C. P. and methanol, herck, absolute were used as received. Bethyl isobutyl ketone was freed of acid by passing it through an activated alumina column. Anhydrous isopropyl alcohol was prepared by distillation from calcium metal turningc. An ee-oe° boiling point fraction was collected. ”imethyl fornamide was purified by distillation. Tetrabutylammonium.hydroxide in isopropyl alcohol nil prepared by the method or hyld and co-aorkers (23). In this method an AMberlite 1.8.A. ion exchange resin was used to convert the tetrabutylammonium iodide to tetra- butylammoniun hydroxide. The ion exchange column, 62 centimeters long, was made from 4 centimeter glass tubing. The column was conditioned by passing slowly 10 liters of l H potassium hydroxide through the column. The column was then washed with 5 liters of distilled water followed by 5 liters of anhydrous isopronyl alcohol. Seven hundred milliliters of isopropyl alcohol containing 100 grams of tetrahutylanmoniun iodide were passed through the column. The throughput was kept at a rate less than 5 milliliters per minute to insure maximum conversion to the hydroxide form. Seven hundred milliliters of anhy- drous isopropyl alcohol were then passed through the column and these washings were combined with the reagent. 11 The 1400 milliliters of tetrahutylammonium hydroxide were stored in a 2 liter pyrex bottle equipped with an escsritooanhydrono absorption bUIb to insure maximum reagent stability. Reagent.solution was withdrawn from this bottle through an all-glass siphon. The tetrabutylannonium hydroxide was standardised against primary standard benzoic acid by'a visual titra- tion procedure. Five drops of thymol blue dissolved in isOpropyl alcohol was used as the indicator. methyl isobutyl kctone or 80% benzene-20% methanol was used as the solvent for the standardization. The indicator blank for 50 milliliters of the solvents was less than 0.08 milliliters. To check the adequacy of thymol blue as the standardization indicator, several potentiouetric standardization titrations were performed. Coed agreement between the two standardisation methods was observed, Apparatus A Ecckman Kodel B~2 p5 hater, equipped with a glass eleatrode and a sleeve type saturated calomcl electrode pair, was used for the potentiomctric titrations. The conductance titrations were performed with a Serfasa hodel ROE 15 Conductivity Bridge. Flatinizcd platinum immersion electrodes (cell constant of 0.1) were employed. Preliminary high frequency titrations were conducted with the high frequency titration apparatus designed and 12 constructed by Johnson and Tinnick (56). It was found, howevcr, in the course of the preliminary titration: curried out, that the apparatus was affectod at timee by line voltage fluctuationc which resulted iu erratic instrument rcsponee. To eliminate or greatly reduce this erratic behavior a aocond stare voltage regulator unit was incorporated in the circuit. Figure 1 show: the circuit diagram of the modified high frequency titration apparatus utilizing a R.C.A. voltage regulator circuit. ihic voltage regulator circuit (52) includes a 5651 voltage reference tube. Only two major modifications were required for the adap- tion of the voltage regulator circuit. Two voltage reference tubes (typo 023) in curios were required to supply the 300 volt Operation level of the second stage voltage regulator. A potential divider at the output of the regulated power supply was added to provide 150 volt- to the 955 oscillator tube. A new instrument, including the second stage voltage regulator circuit, was constructed. Very stable instru- ment cpcretion was attained. fly tests in which line voltage to the instrurent was varied from 120 to 60 volts, only very email changes in instrument response were observed. Zhe real test of satisfactory stable perform- ance was made during titratione. Vary little scattering of points in the titration curve: was detected. High Frequency Circuit Diagram Code (Eor Figure 1) 0.. Cell assembly 61, Cg, Ca, C4. 133 micromicrofarads, mica C5, C5. 20 microfarads, 450 volts 07. 0.1 microfarads, 400 volts L1. HG E/U coaxial half-wave line, approximately 85 centimeters total length L2. 10 turns No. 22 wire wound around R4 L3. Filter choke, Stancor C-1709, any, 85ma. DC. Bl, R4. 15,000-ohm, 1-watt R2. loco-ohm, l-watt H5. loo-ohm, S-Iatto R5. 12,030-ohm, 2-watts 85, R7. 4?,OOO-ohm, 0.5ouatta R3. 12,000-ohm, 2-watts R9. 68,000-ohm, 2-inch: R10. 1,009,000-0hm, 0.5-wutts R11. 15,0CO-Ohm, 2-watta R12. 10,000-ohn output voltage-control potanttometer 813. 5000-0 m, wire wound 314. ISO-ohm, 10-watts, plate current balancing potentiometer T. 350-0-550, QOma.x 5 volts, 3:; 6.5 volts. 58. V2. 5Y3 V3: V4. ODS. va lsq/so V50 6AS7‘GT V6. PSL7-GT V7. 5651 14 h:\.\\x%$®x§x$x\<§\\man\\n\ \b\<.uu\ .V . \ WW§WQ 3%. 9% w ILL J A Q «N A «.a r llllllllll . lkvwavaiMN . 4| 15 The operating frequency of the titration apparatus was moanurod with 3 Signal Corps Signal Generator Eodol l-ZEZ-A and Signal Lorpa Notorodyno flonitor fiodoloBC-l755oA. Tho Operating frequency employed throughout this study out 148.5 no. A Sargant fiodol XXI Polarograph, connoctod across n fixod resistor in series uith the grid leak resistor of tho oscillator tuba, Ill used to detect grid current charges (38). The half-wave coaxial line and tho plate typo capacitativo coll employed were flhoso constructed by Hooaor (31). A 250 milliliter polyethylene bottle was employed as o titration vessel. A motor driven glass stirring paddle oxtended through a amall hole in the cap of the bottle. Continuous stirring was used throughout tho titration. The tip of n semi-micro burst, extending through a amnll hole in the shoulder or the bottlo, Ill immersed in the solution being titrated. Through appro- priate port: a nitrogen atmosphere could to maintained in tho bottlo. Tho rocponso curve for totrabutylammonium hydroxide in the rclatively basic dimethyl formamide was obtained with the solution in the vessel under a nitrogen atmos- phere. A nitrogen atmosphero was not maintained nhilo titration: in which methyl isobutyl ketono or bonzono- mothnnol nerved as solvents. 16 Titration Procsduroo Potontiomotrig Titrations Tho weighsd ommplos IOPO dissolved in 50 milliliters of oithor 805 bonsano-QOfi'mothnnol or methyl ioobutyl kotono. The choics of the solvent depended on the apparent acidity of the acid. The standardization control on tho pH motor was adjusted until the lowest pH valuo, usually one, was indicated on the motor. Titrant'uaa added in 0.5 mil- liliter incrcmonts to the stirred solution. Hear the endpointrthc increments were reduced to 0.03 millilitor. Some of the stronger dibasic acids could not be titrated in methyl iaobutyl kctono using the godol 3-2 pH Motor, because the motor noodle went off scale before tho titration was completed. Conductimotric T trationa Tho weighed samples were dissolved in 50 milliliters of solvent. Titront was added through the buret tip which was immoraod in the solution being titrated. Conductance volues were moaaurcd during the course of the titration with the oscillator or the conductivity bridge Operating at 60 cycles per second. A nitrogen atmosphcrc was maintained in the titra~ tion 708381 only while the rccponso curve was being obtained for the dinothyl fornamido system. 17 High Freguencz Titretions The high frequency titration apparatus and the polsrozrspb eere sllosed to warm up for at least 15 minutes prior to titretions. Weighed samples were introduced into the titration vessel and dissolved in 150 milliliters of solvent. Folsrogrepb edjustments were made so that the recorder indicetor assumed some desirable initisl velue. This was sttsined by selecting s 1.0 volt spen, s 20% bridge setting and s sensitivity or 0.06 microemperes per millimeter. Doenscsle compeneetion ees employed for the final adjustment. when the indicator moved too fer upscale during s titration, it was returned to the initial value by adjusting the downscale compensator. The reagent burst tip extended below the surfsce of the solution being titrated. Reagent see added in .25 to 0.50 milliliter measured portions. Instrument readings were made 30 seconds after each portion of reagent had been added. 18 {1 H (’3 (‘1 ’3 (.4 (x) H 'J «3 C) ijfi A ‘ a L: (—0 f—J ~ 1 U1 Instrument fiespon§g_Curves To obtain the information for constructing response curves. measured increments of titrsnt were added to a known volume of solvent contained in the titration vessel of the instrument being used. Instrument readings for various concentrations were recorded. High frequency and conductimetric response curves a. sore constructed by plotting the molar concentration of the titrant in the solvent being studied against the instrument readings. inosc curves served as useful guides in the selection of suitable solvent-titrent systems and of the Optimum concentration level in the solution to be titrated. The test solvent-titrant system is one ehich yields relatively high and lineer instrument response for slight on ngss in concentration. The optimum concentration level in the solution being titrated is that which yields linear and relatively high instru- ment response when the concentret on changes in the solution. Figure 2 shows the high frequency roeponse curves for tetrebutylsmnonium hydroxide in 80% benzene-205 meth- anol, methyl isobutyl ketone, and dimothyl fornsnido. The greatest instrument response was obtained ehen the 9 1 §§3xyw WW3 Nob .VQQQWMV‘ vxawkuuxsxmwvxwkob Qéx \wnwknvwwtxififix N NVoomk \6 MNNxN WNW huddxx , \Q_. 0 \ 3% .0 \08 .0 \KNQNan &Q% \Q I K \.m .mmva.o moma.o m ;om.m om m4 n.ooa we.m camo.o oomH.o cmooummom mm m.HoH ow.o Hme.o oemfl.o emom.mmom e: w.ooa wo.o amwu.o ooma.o meom.mnom um .Hoa ev.m Hawa.o wowa.o .iomsm.nm cm 0.00“ «v.9 do «a. o ovma.o \ownn om om m.mHH oa.m ”mm”. o woma.o w Moaee=om mm a.eo or.e me~.o wema.o rtoaumeom um v.0m mo.o domH.o eema.o o>momamwon mm a. mo em.o~ mcvm.o emwa.o moon mm w.eua on.w amma.o >wma.o can a: .mou no.» Hmmn.o bmmH.o cmea gem rr Rom.esumq coco oocunom hank?— Aenehw. 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This fact is demonstrated by comparing the percentage purity values shown in Table II for each of these acids. Satisfactory results, calculated on the basis of the second neutralization endpoint, were obtained for adipic, citric, fumaric, malonic, oxalic, sebscic, and succinic acids. In nearly all cases, the conductimetric titration results obtained for these acids were in good agreement I with those obtained by the high frequency and poten— € tiometric methods. ‘ with the exception of the results obtained for the longer chain adipic and sebacic acids, the titration results evaluated on the basis of the first titration endpoint for high frequency and conductimetric titrations sore satisfactory. Titretiqg._£ Acid Kixtures Very little change in the slaps of the successive high frequency titration curve segments was observed for maleie acid. Much sharper endpoints were obtained for fumsric acid then for maleic acid. these results suggested the possibility of resolving a mixture of these acids. Figure 7 shows a typical high frequency titration curve obtained for s titration of rumsric and meleic acid mixture with tetrstutylammonium hydroxide. The results are summarized in Zsble III. w .httfik g ..\< tel c .. Vc.\.\\\\.\.u§\u NRVNENV \<\ NV§RX\\\§\M\ u\%\\&\ .QéQW “two G S<\ Sums u\N\\\\n§\Vb unto .c Kc \<§\\N\\\ 5.x \ NNVVmfiux _,\\m\%.\ WNmNN\V\VV\\< S‘ZJJJW/72/ N Iflfl/f/fl/fl 4775/2; OOH K .op. as N 2 K an mtovmlo enounma ca wane canceou OOH K .unemofl N a K HEAmIo a unaem o» machOAncnheo undone» Ho canao> e a once condom m o o nEahm Mllllliq.l ouoa annuabm w a u a woo.m new.m mam.o mmb.a o n.mb m.¢m men.m the.“ ova.” mnm.o n «.em m.non mom.a nnm.a mad.” mam.o m m.nb o.vo~ men.» men.” ”no.0 moo.” a nouowdm Doahqaom Moscow canoe oaoaem oahuimm edge coeoq canoe once u .uom fiance oao< .eom anodes wme$HHx QHU< UHWQ