1‘ M ¥ l l | )‘a M W l I ‘ ‘ ‘ ¥ i ‘ ¥ ZPIIII ‘W‘I: M'H “ ¥ V H ‘ l i I [t i ‘\ \ ‘ 1 M w | I? F I “r, . "FF-6E WM 35 mmzeg Q‘Pé 'E’R'E RAH Q? 'E‘E-{E' Wéiiéb‘fiéii} a WALLEUM {EH} Exfi’fiéfléfi mam: ER 2.??? SUiWRiC .‘ici'fiEE‘ mm {m the Seem eé’ M. 5. RfliC’EiiGfifl 5mm URii’fiZSW‘! Efiemaéfi Gm Gm!“ 295? — ‘Ilmllflmliniiilmflnmmlmmml L 3 1293 00994 9649 MICHIGM STATE UNNCRSITY ¥ L IBR A R Y Michigan State University fl (,4.-- AF-sj |_./ MICHIGAN 5mg UIIIIIgzsm EAST LANSING, MICHIGAN I '| w» a.“ ‘ O V: (C‘ ks.) 1.»;- THP. EFFECT W (31203102 01" TR! EATS OF THE 111‘“.le (D-TflALLIW (III) EXOLWJ REACTIOfl IN 2.19f SULFURIC ACID 3? Keane ch Ora Groves AN ABSTRACT Submitted to the College of Arts and Selene. Hichigan State University of Agriculturo and Applied Science in partial fulfillment of the requirement: for the degree of EASTER 01' SCIENCE Department of Matty that 1957 ABSTRACT The rate of the exchange reaction between thallium (I) and thallium (III) in 2.19f sulfuric acid was determined as a function of chloride concentration. The exchange rate was found to be considerably decreased for formal ratios of chloride to thallium (111) between 0:1 and 2.5:1 and strongly accelerated above the formal ratio of 2.5:1. The study was limited to ratios below 10:1 since precipitation occurred in the resction.mixturee of higher ratios. The overall variation of reaction rate is on the order of 103, with a minimum occurring at a chloride to thallium (III) ratio of about 2.5:1, followed by a rate increase with a chloride dependence slightly greater than second order. The data were interpreted by a procedure developed by I. Penna- Pranca and I. Dodson (l) in their interpretation of the very enmilar effect of cyanide on this exchange reaction in perchloric acid. Through this procedure an expression was derived which predicted the rate constants for [01"] : [11(13):] ratios less than 2:1 with a precision of 3 8.21. The variation in exchange rate was concluded to be due to the formation of thallium (III) chloride complexes. The relative magnitude of the association constants of the first two of these postulated thallium (III) chloride complexes, TlCl‘* and TlClz’, was determined as 0.0130 for solutions of ionic strength 3.68f. LITERATURE CITED (1) I. Penna-France and R. w. Dodson, J. Am. Chem. Soc., 11, 2651 (1955). the author wishes to express his sincere appreciation to Assistant Professor c. I. trubeker for his guidance and assistance throughout the eouru of this work. ‘0'... i... it 0 TABLE 0? WRTEETS Immw 0......OOOOOOOOOI.O...COCO-O'COOOOOOOOOOOOOOO HISTORICAL on"...u................................... MATERIALS .............................................. PROCEDURES ...............nu..."..................... IESULTSARDDISCIBSIOI "noun........................ 8W! o.............................o................. LITERATURE CITED ....................................... APPENDIX 1: 131:1‘1 fiomrch “8131-10!!! eeeeeeeeeeeeeeeeeeee Page 13 27 29 30 MMWCTIOE midation and reduction reactions are of great import.“ to the chemist. arising from these types of reaction is an increasins interest in the node of electron transfer which occurs. Electron en- thugs reactions. which involve the simultaneous entidation and reduc- tion of stat of the one eluent without affecting the overall cen- centrstions of the two oxidation states. are of great interest because they represent the si-plest oxidation and reduction reactions ad any even involve the direct transfer of electrons free one species to the other. the rate of electron-transfer reactions is the tool. obtained fru such investigations, with which the chalet hopes to anyone the actual path used by an electron is trmfsrring fr. one species to another. Various factors nay severe this rate of transfer. (l) The usher of electrons involved should be considered; that is. the transfer of two electrons new be nucb nore difficult than the trans- fer of one. (2) llectrostatie charges of involved species with like sign any hinder close approach and decrease the probability of elec- tron transfer. (3) The structure and composition of the reacting species is inportant. For steeple, groups ”rounding the central ata- (e.g. n30. m3. 61‘. or) an hinder electron transfer by inter- ferring with the extension into space of the orbitals involved in electron transfer. or they may aid transfer by increasing the sites of the reacting species and decreasing the forces of coulonhis repul- sion between then. Another possibly important factor is the similar- ity in the structures of the reacting species. According to the trench-coed» principle. electronic transitions are very rapid towered 2 to the notion of nuclei; and. therefore. the most probable electronic transitions are those that do not require the relative position of the Insolei to change. (i) The environ-ant of the reactants is also a factor; metallic conductors in solution nay offer an easy path for electron transfer and thus catalyse the reaction. All of the above factors any effect the rate of electron trans- fer. but too little information is available to evaluate their relative worm. in this uperinentel work the third factor is thought to be the nest influential. The sensitivensss of reaction rates due to the addition of various anions such as chloride. cyanide ad nitrate. which are capable of fanning ccnplsnss with one or both of the reactants. has been observed by several workers. fie purpose of this work was to study the effect of chloride on the exchange rate of the thallit- (Ir-thalliu (Ill) reaction in sulfuric acid of constant ionic strength of 3.6M. HISTGRI CAL 'ihe thalliun (l)-thallinn (Ill) exchange reaction was firat investigated by two groups of workers, G. Barbottle and l. Dodson (2) and I. Prestvood and 15.. m1 (3). Both groups have extended their work and have inreetisatcd the kinetics-of the reaction. Under all the conditione that but been etudied, the reaction rate has been found to be dependent on the first power of the thallinn (I) concen- tration and the first power of the thallim (1n) concentration. Frost-wood and Hahl (3) have obaerved the effect on the rate constant of the thallinn (D-thalliun (Ill) reaction in perchloric acid at a constant ionic strength of 3.681. with variations in the concentrations of the reactants. the hydrogen ion concentration and the nitrate concentration. Their results indicate a decrease in re- action rate with incrcaaing hydrogen ion concentration. the depend- ence of the reaction rate with door-caning hydrogen ion concentration in interpreted as being due to the increase of an active exchange apecias forned by hydrolysis of tho thalliu- (lll). hon kinetic data they interpret thir reanlts in terns of two reaction necheni—s: (1) 21* 4 in“? —->r1“‘ ¢ en" (2) 11* . *11w"-—) rm” e rut“ . a third nechenie- of electron transfer is proposed for nixtnrcs con- taining nitrate ions: (3) 'fl" 9 "1503“ -—? 11303“ e “'1’ . They have slao doterninad the variation of the exchange rate of the reaction eiatnre in the preeence of pleural black and silica sol. The half tins of exchange for the reaction in the preeence of platinu— 4 black was decreased by a factor of 40. The presence of pulverized silica gel resulted in no measurable change in rate. G. Barbottle and l. Dodson (2), working with mixtures of sodium perchlorate and perchloric acid in which the ionic strength was main- tained at 6.0f, studied the variation of exchange rate with decreasing acid concentrations. They also found that the rate of exchange de- creases with increasing hydrogen ion concentration. They suggest that hydrolysis of thallium (III) ion occurs and that the hydrolyzed species exchanges more rapidly. They interpret their data as indicating that both thallium (III) and hydroxo-thallium (III) are present in signifi- cant concentrations, but only the hydroxo-thalliun (III) exchanges with the thallium (I). These results are in agreement with the previous work of Prestwood and Hhhl (3), but the variation of exchange rate does not follow the Prestwood and wahl rate law. More recently c. H. Brubaker and J. P. nickel (8) have investi- gated this exchange reaction in 2.19f sulfuric acid solutions of the same constant ionic strength, 3.68f, and hydrogen ion concentration that Prestwood and Nahl (3) had used for their investigations of the reaction in perchloric acid. They found that the rates of reaction are about 200 times those reported by the latter investigators. They have correlated their data with the following equation __n_. 0.0345 c 0.7(n*)2(304=lo 12(si)z(soé,=23 ab [(ntflo twp) 4 rlrzo :3 (305)] [1 e £45043] where K1 3 (WE). K2 : (uoqgnt) (T1’3) (floued) ‘3 I (T1504’> . K4 r (TISOA‘) (Tl‘3)(304:) (Tl*)(8043). 3 They have suggested that e coeibinstion of exchange processes such as m” . 1150,; ——s u” i. also; «mo: 0 ‘l’l(30‘)3§ -—)'rlso‘* e mmmfi" nay be the reason for the increased rate of exchange. in worhers have used the assmption in: the activity coeffi- cients of the reactants are constant at constant ionic strength. the decrease in rate with increasing acid concentration could be ntirely due to changing activity coefficients of the reactants and transition states involved in the transier'nechaniens (7). I ' I ' Dodson and harbottle' (2) have also investigated electron trans- for rates for aisteres‘ containing nixed hydrochloric and perchloric acids at constant ionic strength 6.0£. They com: in. rate to be considerably depressed by low concentrations of chloride. while it is strongly. accelerated at higher chloride concentrations. The uni- rate occurs at. a [61']:['l’l(lll)] ratio of 1.3 and subseqnently rises. the in- crease is little less than second order in chloride. these data. eup- ple-ented with transference semi-enacts, were interpreted as resulting in. .5. (oration of thalliiss (m) chloride complexes. 'l‘hs initial depression is believed due to the {creation of less reactive 1161“ and 1161;" species while the acceleration upon increased chloride eon- centratioa is believed due to the (creation of a sore reactive 1101" species and possibly a weekly associated thallii- (1) couples each as is. 11:21,: or new”: proposed by lrouhers and Lib (6). The postulated existence of stable thalliua (m) chloride misses is compatible with the observations of Benoit (5). who has estinated dissociation constants of 10'3-1, 10‘5-5. 104-2 and 10-2-2 for the successive cole- plexes from 'i'lCl‘M to IlClg‘. a. Penna-France and a. Dodson (4), working with reaction mix-- tures of cyanide and perchloric acid solutions of constant ionic strength of 0.5f. have observed that cyanide has a drastic effect on the rate of electron exchange. a.total variation of about 10.000 fold in the rate is observed. small amounts diminish the rate. a minim at less than 11 of the initial value is observed at e [CN']:[TI(III)] ratio of 3.5. followed by an increase in rate about as the third power of (CN’). They believe the rate variation is best explained by the intention of thalliung(lll) cyanide complexes. The initial effect is attributed to the formation of TlCfl** and thflz’ complexes which are inert to the exchange reaction. The increase in rate is ascribed to the formation of higher thalliun:(lll) cyanide complexes. They infer that Tl(CH)3 or 71(Cfl)4‘ reacting with 11* are responsible for the increase near the ninhnun. Evidence for the lower complexes TlCh“ and TlCN2* is further substantiated by kinetic data which enabled them to calculate the relative ugnitudes of the equilibrium constants of these two species. MATERIALS ‘Ihalliu (I) nitrate was obtained from 2. H. Sargent and company. sodius dichronste tron Merck and Company. sodium cyanide iron the hellinchrodt Chemical aorta and all acids and cunning hydroxide iron l. i. do Font do lie-ours and Company. Radioactive thallium (T1334) was obtained as the nitrate irons the U. 8. stoaic Energy Couiseion. Oak Ridge. 'i’cnnessee. The thallius (I) sulfate and radioactive thallit- (ill) sulfate solutions used were prepared by c. Knop according to the procedure outlined by J. P. nickel (12). the thalliu (Ill) enlists solution was prepared (roe a sat- urated solution of recrystallised thallium (I) sulfate. the sulfate was oxidised to thallii- (III) oxide with potsesiu hesacysooi‘srrate (III) in 0.1! sodirn hydmide. the oxide was washed true of hers-- cysnoierrate (11) and (ill) by decanting the supernate and caching with distilled water. Thellin- (Ill) sulfate was then prepared by dissolving the oxide in 20 :1 of 10. 61 sulfuric acid. The voices o! solution was increased to 200 nl. ‘i’ns resulting thalliu (ill) sul- fate solution was anelyrsd for total thalliu content by reduction and precipitation as thalliu (I) chroonte. The thallius (ll!) con- tent ot the sulfate solution use determined with another s-ple by precipitation as the oxide. 'ihe procedure used in both precipitations is described by Well and Hillsbrsnd (l). The analyses agreed within 1.01 indicating that the thallium content of the sulfate solu«- tion is essentially completely thallius (III). The residual sulfuric acid concentration was calculated by determining the mount of sulfuric acid which had reacted with -‘~A“l a 1 I\\- thallius (III) oxide according to the reaction $1103 + 3.112305% Tl;(80(.)3 i- 3820. The count determined was then subtracted iron the initial tomlity of the acid, indicating the toruslity of the residual sulfuric acid in the sultate solution. A standard sedit- hydroxide solution was prepared tree of carbonate and standardised with potassit- scid phthelate. Itandard acids were then prepared and analysed by cmarison with this sodiu- hydroxide solution. All a! the reactions were run in 2.192 sulfuric acid solutions. Pro- equilibrius concentration oi sulfate. bisullate and hydrogen ion data obtained by I. II. with (9) and by a eethod described by ‘l‘. r. Young and L. A. Blats (10). J. P. hickel (12) has calculated the ionic strength of a 1.19! sulfuric acid solution as 3.68:. since the concentration of added chloride ranged between 0.009“ and 0.061 . its eiiect on the ionic strength of em solution was considered negligible; and a constant ionic strength of 3.682 is unused for all reactions. lbs concentrations of all solutions in thelliu (I) and thallius (Ill) were variable. they ranged between 0.010,!“ 0.006“ in thallium (ill) and 0.0101 to 0.0031 in thallium (1). depending upon the tonal concentration of the chloride. All reactions were carried out in 100 el volumetric flasks. PROCEDURES ’ leectioa airturcs uere prepared by the addition oi an appre- priats .ount at each stock solution to 100 al van-atria flasks. 'l'be sulfuric acid was first added to each (lash. iollowed by the «cum o! the mun- (1). mum (In) and hydrochlorie acid solutions. W distilled water was then added to each (lash ts bring the final voluae to apprcaiastely ens al less than 100 al. The flasks care than i-ersed :- a water m kept at 3.91.3 0.01%. 'lhesetlashsr-ainediathsbathtoratlaaatthraahsersiasrder tor the solutions to reach thornsl equilibriu- bstore the active thalliu (ll!) sulfate was added. The active thalliu (Ill) sellate was then addod (l.2 al). the flask was then shaken and brsuzht upright twelve tines. the sero tine was taken as the ties o! first shaking. Separation oi the cai- detion states was eccoaplished by precipitatiea oi the thalliua (I) as the chrcaate. The tirst precipitation was usually done within three minutes. Before each precipitation a mataan !5‘0. 2.7 on iilter paper was dried for at least one hour and weighed. Freshly prepared precipitant was used for each precipitation. lbe mitten e! the precipitant was sodiu dichronata 0.2!, sodium cyanide 1.0!. mil- hydroxide 9.01 and 101 by volt. ethyl alcohol. The precipitant Isa saturated with thallim (I) sulfate. filtered. and stored in an ice bath prior to use. he. data obtained by J. r. nickel (l2). halt tines for the isotope exchange were calculated and tan precipitations were tiled to vary between earn and ten tines the calculated half tine. lO A.5 m1 aliquot of the reaction mixture was pipetted into a 150 ml Erlenmeyer flask containing twice its volume in freshly prepared precipitant, except for runs in which the total thallium content was approximately 0.01f, in which case 10 ml aliquots were used. The solution was swirled in an ice bath during the addition of the sample to counteract the heat of neutralization. For more efficient separation the aolution.waa allowed to age for at least five minutes before the thallium (I) chromato was collected on a filter. The filtration was carried out in a steel funnel with a removable chimney. The filter paper was placed on the flat support and the chimney on top. At the point of contact with the filter paper the chimney was 19 mm in diameter. The filtration was aided by an aspirator. Included in the aspiration systemlwas an arrangement for bleeding in air in order to completely control the rate of filtration. Too rapid a filtration greatly reduces the efficiency of the separation. The time of con- tact between the precipitate and supernate from precipitation to separation was kept to within thirty minutes in all cases. Preatwood and Hahl (3) have shown that the heterogeneous exchange between the complexed thallium (Ill) species and the thallium (I) chromata is very slow and would be negligible under these conditions. After filtration the precipitate was washed with four 0.5 ml portions of the precipitant followed by four 0.5 ml portions of distilled water. The chimney was removed, and the precipitate was transferred to a metal plate. A natal cylinder was placed on top of it to prevent the filter paper from curling upon drying. They were dried for at least one hour at 110°C, weighed and mounted on 3% x 2% inch cardhaard cards which were marked for centering. Cellulose tape was placed directly ll war ths s-pla. lash sapla was located directly in front at and tufrosthssssinchsadwisdusfaO-Itsbs. autumn. nodal l. sums-139 saalsrwssesnssctsdtsthsO-Iltwbs. Insults hadaflat platsusfsverwslts. 8-pluwsrssswatsdssisas voltage 100 volts above tbs "toss". 8-pls wsights warisd (raw 7 a. tall-a. fissqlssssuallywsishsdtstwssamussduu. law- sssr. Mensa tbs rats of filtration of tits psasipitstss iawslwiq ths l0 al aliquots was incrsassd ts kssp tbs ssstast tins bstwssa presto pitats ad supersats um. tbs thirty-limits li-it. tiara was sass loss at precipitsts and 7 . 10 la sqlss nssltsd. lbs s-plss wars sswstsd ass: as interval of tiss sufficisstly Imusbtais 10,000mts. hawarajssfthrssswshesustiu intervals fassscts-plswsssssdssthsssstsstwalss. Illasdssa ti-sfsrthsc-ltsbssssdisthssswswasdsm"sss. antacidssssasdtsstgrsnsdserrsatisssssrsasdsfsrssshrssdina. lgsilibriu spacifis sstiwity was tahas ss tbs activity of that s-pls pmipmua an: a can istarwsl .1 tan m: m... Iiass cs- nu life of 1'12“ is to ysars. it was sssscassasy ts ssrrsst for radis- aatiws (stay. Whalitinsswsssttsadstsmssafs-araphsstlu (1-!) mass tins. whats I is defied as tbs ratio 0! tbs spacifis activities (until. rats par a; of ants) st tins t to tins t... (tss tisss ti). Mmphwasssspsndwsiaafr-sia tsainssv psrinsstal points. Ists sssstasts wars uleslstsd fra- hslf “ass and ancestra- tisss st thalliu (i) .6 (m). craphs sf sachenas reactions with 12 short lull the. wily an mount atuuht nun. lunar. graph. of then. anchnaga reactions linolvlns lot; halt ti... Ilrl 0.0“... «attend. Int-n mutton: oi tlu ultuhtod'hou than of then nations mu within 3 101.. This Intu- mum in 1: sxrcuont with that animal to thin rated... by Drunk» ad Itch]. (O). 13 SESL TS AfiD BISCfiSSZOfi The variation in rate of the thallium.(l)-thellium (III) ex- change reaction in 2.12f sulfuric acid of constant ionic strethh was detenmined as a function of chloride concentration. The rate data were interpreted in teams of the Rainy (ll) formula, applicable to exchange reactions which are first order in the overall concentration of each oxidation state and occur at equilibrium ln (1 - x/x-) c - Bjab (n O b)t. The x and x,, are the specific activities at time t and at infinite time (ten times ct), respectively. Specific activity is defined as the ratio of the activity in counts per second per milligram of pre- cipitated thallium (I) chromete. The a and b are the overall formal concentrations of thallium (I) and thallium (111). respectively; and R is the rate of exchange of the electron transfer reaction in units of formelity'ltime’l. The rate of exchange of the thallium (I)-thallium (III) re- action in 2.19f sulfuric acid was shown, by C. H. Brubeker and J. P. Euckel (3). to be dependent on the first powers of the thal- lium.(I)-thslliwm (Ill) concentrations. They assumed °‘ 49 a a k [11(1)] [mum] and found that alpha equals 0.98 3 0.06 and beta equals 1.00 3 0.01. The half time of reaction. the tire when x/x. equals 1;, can be evaluated from a plot of in (l - xlx¢,) versus time. Typical exchange rate data interpreted by the above formula are indicated in Figure I. 1.0 0.9 0.8 0.7 0.6 0.5 0.4 l-x/xm 0 ~ 400 800 r 1200 Minutes Fig. I - Typical rate data. (have A, [Cl' :[T1(III)] 0:1, curve B, [c1']:tr1(111)] 0.87:1; curve c, c1']:[n(1u)] 1.06:1. 15 Itossbssssnisl'izurslthststtiussrothsrsisbstusss 51. slid 101 subs-p isdicstsd. his sppsrsst sore-tins 'snhsnxs is duo to ss sceslsrstsd «classes rsts semis; either during tbs short :1.- bsmssslixisssnd sspsrstissordvris; ths upstart-s. w. 5, hoping the haunt oopsrstsd sud tbs. rsts of precipitation so coco stsst ss possibls tor sll procipitstioss of soy givss res. the error on u m. We sore-tins exam. will to (“an tutor as not offset the slope of the m ,1». m- which tbs n1: tins of rssctios u dstsrsissd. m. 51. to‘ 101. some sore-tins mum. is is oars-out with provisos sort (2. I) so this outage rssstios shore sspsrstios oss effected l7 prssipitstios o! thsllii- (I) M. ,. Iubstitutiss m. u.- shove sqsstiss. six. 2 r us.- c I :5. gives the suction I/st '8 0.63915“. 4 ms. Thus. urn-quummu truthshsvssssssstrstisssois-dt sad the ssssurss hsli tins of rssetios. lbs offset o! incrsssis. chlorids essssstrstios so the rsts o! sxchsngs is shot: is l'sbls I. It sss be soon thst the rots of sschssss is ctr-sly sensitivs .. .....u.. 1- am“. sssesntrstios. no man «he: 1. s asses! sssrssss is rsts tollovsd by s “drsstis rsductiss is rsts stsrtis; st ss spprosissts [61"] x [11011)] rstio o! 0.311 sud roset- m s uni- st s [or] : [runn] rstio o! snrszisstsly 3.531. A: m. point the ovorsll cum 1. s m. docrssss on tho ordsr of 100. At highsr [01"] a Damn] the rsts sgsis incrsssss with s chloride upssdsscs slightly xrsstsr thss second order. the study no lisitsd to H 16 e sexist-[GP] 1 [THUG] retic of 10:1. Preperetios of reection sutures shove e rstie of 1011 see scccspsnied by the ferssties of s precipitete. the precipitete hes ss espiricsl fouls. 112613. 1131.11 mil“ 0! KIWI Mn 0! 011101101 calmne- AT 1593:. P ' 3.“. I389‘ ' 2:19! ' ll 01"(1) flaunt) 11(1)“) cl'muu) All.» 151.11.) 0.000 ' 0.0105 0.010 0.00:1 0.794 40.5 0.0091 0.0105 0.010 0.000:1 0.107 205 0.012 0.0115 0.010 1.00:1 0.0095 300 0.014 0.0115 0.010 1.23:1 0.0405 005 0.017 , 0.0115 0.010 ‘ 1.49:1 0.0157 2.545 0.025 0.0115 0.010 2.00:1 0.0020 13.240 0.025 0.0115 0.010 2.17:1 0.0021 15.400 0.027 ' 0.0115. 0.010 2.55:1 ' 0.0019 10.410 0.055 0.0114 0.010 3.07:1 0.0025 12.900 0.025. _ 0.0005 0.005 5.15:1 0.00405 14.750 0.050 0.0005 0.005 4.01:1 0.00041 9.400 0.035 0.0004 0.005 5.47:1 0.00920 0.500 0.001 0.0005 0.005 9.53:1 0.0544 1.000 the effect en the rete of rssetios with increesisg chloride tell he espleissd es the sue hesis thet I. H. ledscs end «waters (2. 4) here seed in their interpretetios ef the effect ef chleride sud cysnide A es resetion retes in perchleric scid ef keenstest ionic strength “.00. the initiel reducties is the eschenge rete sen he esplsined 011 the hssis ef the fersstios of thsllius (:11) couples“. mes complexes epperently ere ef such s neture ss te disfever e rspid electron eschsnge lecheniu. This vill result in s decresse in the coscentrsties of the C . . , . I . . . . . - . . . . _ -- 'v C ‘ O . . K . . . . ,. _ . . . . - . . . . - 1 _. -‘ O ‘ ‘ ' ‘- a u N " ' U I l ‘ . . . 4 : I u . e l ' a . I ‘ O C . i. V . . . 1 . , i s e 0 . e f - -' . . : . s s - e .. v A ' . 1 I e ‘ I o 1 . C I ' | C I v I l o ) ' l I c s s . e ’ . s s . e s . , 7. I s . ~’ 1 ' 9 e o . . . . : , v . ., . . —.—- . .y - . . v . . . - -4, - -O , s O --as a . .. -- ~ . e - a. n - O ‘- ..s -4. 0-..-.. -u . . '1 1 _, 1 . 7: . . U " : , _ ‘ , J 1 1: ',. ‘ 7 .: 7 : 1 . . I . J . 7 f: ' l I , J , . 0 . . «, , e ' , 1 . ‘ 1 .. , : . t; ‘ L . . 17 011.111:- (111) new: species sorsslly present is the m of chloride ssd e eshsewest decreese is the eversll resetios rote: the soet prohshls forsssf the eagles thelliu (111) ioss ere 'l’lCl” and 3101:” be nest-9th. fist the thelll. (111) end not the M“. (I) um1mucqm‘mmuwummumc (5). mmum11ummnc1“unc1{uumuuu-uu um. mum 0111: «societies oosstente 0:: 11:. order .1 10‘ set 103. respectively. has-thee support for this seen-puss is pines fro- therecestworheflsiresdleseollee (l3). Mhewesssesredthe «societies sosstset for the l'lCl species esi ehteisse the also 1.0 ethD‘C. Misadthiswslsewiththeeessluesehteissdhy leseit (3) for the thslliI- (111) eta-pisses isdioetee thst the letter wouldhetheprsd-isestepeciee. nenheeessstiscreeseisrstsef reestioe is W to he 0::- u the forsstiee of 1101, end run". which spperestly have s pester shility to esohsece thee the 'l'lCl” ssd l'lclz’. 'nae eeseeietios eossteste for these letter misses were else detenised by 1.001: (5) «:0 0.:- estissted a be .000: 101. If the iscreeeed rete is capletely dse to the forsetios of nabs-02101;. thersteefeschsusshosldspproschsesssteet welue whes ell of the thelliu (Ill) hes Mined to fore the 11le 0.91011. we should scour seer e [01'] :[r1(111)] 1.110 of 4:1. has seesnisstissef'rshlelitcsshessssthstthieissottheoeee. the essstsst rete increese fra e [Cl’]1['fl(lll)] rstio of hi to 10:1 sest he due to the fonsties of wesh thslliu (I) chloride cos- eleses which eschews rspidl; with 71m. The forsetios of such thslo 11:- (1) when es r1013: end r101": hes 0000 poetulsted 0y Ira-sen end 1.11: (6). ‘ 18 The exchenge rste dsts.were snalyeed by s.method used by l. Penne-rrence end I. H. Dodson (4) in their enelysie of the thal- lius (I)-thelliun (III) reection in the presence of cyanide in per- chloric acid of constant ionic strength (6.0!). Included in the enelyeis ere dete on exchange rates for the reaction between e [61"] 1 [11011)] ratio of 0. 185:). and 0.74011. 001.1004 by .7. 1. 1110101 (12). ‘ The following teens are defined: [Tl‘3] 3 A . total uncouplexed thallium (III) [mun]. 1° totel 10mm: (111) [01-] e 110 [1101”] : AX [1101f] : ex, :5 s [1101”] / [11"][01‘] ‘6 a [1101;] / [3161“] [01"] r “zleoo (111501.12 or 4.51:1 16 AX2(A) K5 AX: The concentrations of chloride and thallium (111) can be ex- pressed es (2) x0 e Ax + 2 AX: assuming ell Cl' is complexed end (3) A s ‘0 - AX - AXZ upon substitution of equation (2) into (3) (4) AX e 2 A0 - X0 - 2 A end (4) into (2) (5) AXz e A. - A0 0 X0 19 The following relations are defined Nagsyo; weosylselesoeyzzlo/eosoc upon dividing equation (4) by A0 111/10 3 2 - xo/Ao - 2 4/110 or ’1: Z-ZyO-o‘ equation (5) by A0 szleasA/Aooxo/Aoo 1 or and equation (I) by AD 1/4, : (mzuo) We 7. :0 lo 1512 r 5J2 - be '002 K5 12 x5 0" 1 1 ya) 01' upon rearrangement (a) 16/15 : hm- 1 +42) (2 - 2y. - «)2 If one assumes that neither AX nor A12 react. and that higher cae- plexes may be neglected for alpha less than 2, than h/ko g ’0' where h is the observed second-order rate constant; and k. is its value in the absence of the complexing agent X. The results obtained upon substitution of appropriate alpha and hike values into equation (6) are indicated in Teble II. "a ": h-.- .‘u—av.-_.. ---_.._ -. - -_- w>h - - usquarros (0;, 07.9: r1 010:1 .1... m. 5.1:: 50.740 0.2701 0.0255 0.500 0.2095 0.0194 00.920 0.150s 0.0511 1.04 0.1112 0.0509 1.25 . 0.0009 0.0021 . 01.59 0.0259 0.0515 1.49 0.0172 mg in. 0.0515 Tun» manor!“ re- 5. . 1mm (ti) . 11 appears 0...: the value we, is essentially a constant. with an swarm wales of 0.0310. mum-u: .5 equation (5) and substitution of 0.0515 fer 5}" gives as equation of the fore 1.5 (7) 37.1 9 p.071- 0.554) - 0.0504 (2 .07.)! I 0. this expression was solved for 7. ad evaluated for values of alpha bet-sea 0.183 and LCD. nears-athetweeetheectuelwelsesefthereestieerate sad :1.» 00:51.04 0..“ u:- m equation (1: predicted) 15 indicated in Table 111. ramm (Dominant (111) 1510111001 111 m alpha *0. 105 $0.270 00.663 00.140 0.0“ ”.926 ' 1.060 1. 230 *1.390 1.090 l. 60 1.70 1.00 01.03 70 0. 0196 0.7251 0.5479 0.2420 0.1950 0. 10“ 0.1040 0.0502 0.0240 0.0145 0.0079 0.0040 0.0020 0.0000 Oh wilues obteined Ira J. 5. Make]. (12). TA!“ 11: ' 21 2155111101 a 01102100 1r 25°01. 1. WW 1 1 “mm-:11) h(predieted) 0.00 0.00 0.02 0.50 0.41 0.45 0.22 0.20 0.17 0.15 0.12 0.12 . 0.090 0.005 0.049 0.000 0.015 0.019 0.010 0.012 0.0003 0.0051 0.0014 0.0025 0.00004 1. Deviation 2.0 1 0.4 6., 9. 1 12.0 0 8.0 10$ 5.5 10.3 0.201 R , (f'l min'l) 10’2 10'3 22 I I l IIVI U U i 11715 I . I O I O / 1 11111111 1 11111411 1 ’— 10'I 10° 101 Fig. c1'/'rl(111) II - Exchange rate as a function of chloride concentration. Broken line represents the calculated reaction rate curve. Solid line represents the experimentally determined reaction rate curve. <:> , reaction rates determined by J. P. Nickel (12). 23‘ Figure 11 is a 103.103 plot of reaction rate versus [61"] l[‘1‘1(lll)] . The broken line represents those values of h obtained from equation (7). and the solid line represents experimental values of the reaction rate for the higher [61"] 2111011)] ratios at which the asemnptione made in the derivation of equation (7) are no longer valid. the close agreements between experimental and predicted values for the rate constants lend support to the esmptions eede in the derivation of equation (7)1 (l) neither AX nor AX; react; and (2) higher complexes may be neglected for [61"] :[Tlunfl ratios less than two. Apparently the formation of 'ilCl” end 1'1le hinders electron exchange. This hindrance could be due to two factors: (1) the coulonbie repulsion of species of like sign; end (2) the dissimilarity in the structures of reacting species, assuming the thallium (I) is present essentially as the 1:1" ion. At low [Cl'J:[l'l(lll)] ratios the predominant species are probably 'l’lCl” and 11*. Since these postulated reaction species are well ions with a relatively concentrated electrostatic charge, the coulombic repulsion effect any be the most important factor. For [61'] 1['l'l(lll)] ratios from 1:1 to 211 the predominant species are most likely 111312" and l‘l’. and in this case the dissimilarity in structure may he the important factor contributing to the retardation of the electron transfer. The increased rate, evident after a [Cl'] :[THIID] ratio of 2:1. is thought to be due to two phenomena: (1) the formation of higher thallius (III) complexes. 11613 and 11614“; and (2) the formation of thalliu- (l) chloride complexes. Possible mechanisms, involving these complexes, which favor electron 2!. transfer are (l) *‘l‘lCl3 . rlc12- -—>rrlc12' e rlc13 and (2) «new 1 r1c13= —-)*1'1le 0 new. Mechanism (1) is considered to be favorable to an increased electron transfer rate by virtue of the absence of a coulomhic repulsion be- tween reacting species and structural similarity of the reacting species. Mechanism (2), at first glance. seems to disfavor rapid electron exchange because of coulombic repulsion effects; however, if the sizes of the reacting species are considered and the fact that the existing charges are spread out over a large ionic surface area, the structural annilerity effect may very well predominate. Consideration of the chloride and the very similar cyanide effect on this exchange reaction scans to favor a mechanism for the electron transfer reaction in sulfuric acid (8) siniler to the type shown above. It may be that the increased exchange rate, compared to that observed by Prestwood and Hahl (3) in perchloric acid of similar ionic strength, may be best explained by the combination of processes frusogr 9 n’——->ruso4)' 0 *n’ and “1604);" 9 Il(soa)'——y*‘l'l(804)' 0 1160102.. The coulombic attraction effect afforded by the previously suggested processes (8) are overshadowed by the more favorable mechanism of electron transfer through a sulfate bridge indicated in the above processes. 25 The value of 0.0318 for the ratio of the association con- stants of the T101” and TlClz‘ complexes is not a true prediction of the relative magnitudes of these species. It was assumed in the derivation of the expression which leads to the evaluation of ‘6/‘5 that A. the total uncomplexed thallium (III), was in the for-.of the Tl*" ion. This was certainly not a valid assumption. Brubaker and nickel (8) have shown that the thallium (111) species in 2.191 sulfuric acid is both hydrolysed and complexed with sulfate. There- fore a s [evil s [110*] o [1109th e [1130;] . [1132.] where 510‘] e I: EI'IOH’EI; [TlOH‘fl e I} [11273] E! *3 [H '3 [nsofl e :3 [mod] [304:] g [110?] 3 total uncomplexed 11*3 As Erl’fl 3 [110.3 5.251. e 5.]. «0 K3 [804:] e l [hdJZ [hf] The values of the K's are K1 s 0.77, K2 3 0.071 (14), K3 s 2 (15.8). The values of H’ and 804: for a 2.19f sulfuric acid solution are 2.90f and 0.70f, respectively (12). Evaluation leads to the equation A g [11”] s 2.44 Enf’] Since it was assumed Ito/ts .' 51”] nelz’] r1c1" 26 then the actual value of the ratio is K5/K5 s 2.44 [110”][r1c12'] [mutt]? a 0.0313 Benoit (5) has detenmined the values of K5 and ‘6 at infinite dilu- tion to be 1.28 a 103 and 3.16 a 105. respectively. These values were corrected for applicability with solutions of ionic strength, 3.68f. These corrected values give the ratio K6/K5 to be 0.0037. The deviation of this latter value from the value 0.013 is not surprising since the activity coefficients used in correcting Benoit's values were only approahmate in nature. Activity coefficients were selected so that the ionic sine and vaLence type were comparable to the species involved in each equilibria. Values for the activity coefficients of the actual species have not been determined. 27 sonar The variation in rate of the thalliu" (l)-thalli\n (111) electron exchange reaction in 2.19f sulfuric acid has been deter- mined as a function of chloride concentration- The overall rate of exchange was found to vary by a factor of 103. The initial effect of adding chloride to the syst- vaa a rapid decrease in aschangs.rate. This effect was attributed to the forma- tion of the thinn— (ll!) chloride complexes, T161“ and Half. which are apparently inert to an electron exchange. A minimum rats was observed at a chloride to thalliu (In) ratioof about 2.5:1. folloved by a rapid increase in exchange rate. This increase in exchange rate was attributed to the formation of the thallium (In) chloride capleaes run, and not“. The increase In. .a chloride dependence slightly greater than second order. .The failure “of the reaction rate to approach a limiting value was believed due to the formation of thallit- (I) chloride complexes favorable to a rapid exchange mechanism. Exchange mechanisms have been proposed. Those which appear favorable to an increased reaction rate involve electron transfer through a chloride bridge. By «suing (1) that higher cmlsaes above T101“ and 11le may be neglected for [cu]:[r1(rrrfl ratios below 2:1 and (2) that new and Hal; do wt reset. it was possible to derive an expression which predicted the rate constants for this reaction uith a per cent pre- cision of e 8.2 for [c1‘]:[r1(m)] ratios less than 2:1. Inrther mathematical development afforded an evaluation of the relative magnitudes of the association constants for the 11le 28 and run“ esmplexu. Ooructise for hydrolysis and enlists complex tonesticn save a value of 0.013 for the ratio ten, in solutions at constant ionic strength. 3.68:; where K; x [1101“] . K6 2 [11613. ‘ BNlEcv] [new] I er] . 29 LITERATURE Club 1. Hillebrand, H. 1., and Lundell, G. I. L, Applied Inorganic Analysis, 2nd Ed., John Riley and Sons, Inc., New York, 1953. 2. fierbottle, 6., and Dodson, I. 8., J. In. Chem. Soc., 12, 880 (1948); _7_3, 2442 (1951). 3a h‘fltWOd, ‘e Je. ‘nd "“1. As CeglJe be them. SOCe. 2-9.. 880 (1943); 1_1_, 3137 (191.9). 4. Penna-France, 1., and Dodson, R. 11., J. Am. Chen. Soc., 11, 2651 (1955). 5. Benoit, 1., Bull. soc. chin. France, 5-2, 518 (1949). 6. hcmhers, 11., and Lih, I. 11.. z. physik. mesh, A153, 335 (1931). 7. Rossetti, r. J., J. Inorg. Nucl. 011%.. l, 159 (1955). 8. Brubaker, c. 11., and nickel, J. P., J. Inors. Nucl. Glam, 3, 55 (1957). 9. Smith, 11. 11.. PhD Thesis, University of micago (1949). 10. Young, '1'. F., and Blatz, L. A., Olen. Revs., 43,98 (1949). 11. Many, B. A. 0., Nature, 142, 997 (1938). 12. nickel, J. L, PhD Thesis, Michigan State University (1957), in print. 13. Hair, V. 8. K., and llsncollas, c. 11., J. Chem. 80c., 318 (1957). 14. Biedernen, 0.. Arkiv £3: Kemi, g, 441 (1953). 15. Bell, 1. 8., and George, J. 11. 3., Trans. Faraday Soc., 42, 619 (1953). APPENDIX I INITIAL enema! “81m 30 The initial research assignment was the preparation of compounds characterised by metallic ions of large ionic since, high charge, and which are not extensively hydrolysed in solution. The preparation of platinum (1V) chalets compounds was considered to be the nest promising approach to the solution of this problem. Initial interest centered upon the preparation of a tris (2,2 dipyridyl) platinum (1V) compound. An extensive preliminary search through the available literature revealed that the preparation of this compound had not been previously reported. However, preparations of similar com- pounds, e.g. Ih(dipy)3 C13'31120 (l), 0e(dipy)3 013-1120 (2), and lumpy), c1; (3) [where "dipy" is 2.2 dipyridyl] had been reported. The procedures for the preparation of the above complexes were noted with a view that similar procedures might prove useful in the synthesis of the tris (2,2 dipyridyl) platim. (IV) coupler. The first attmpt at a synthesis involved the dissolution of Hzl’tCla in a saturated aqueous solution of dipyridyl. Upon heating and separation, the filtrate yielded a, small mount of a red, waxy compound and the residue consisted of a yellow, fibrous, extremely insoluble compound. Analysis of the residue indicated that this canpound con- tained 39.31 platinum. It was believed to be Pt(dipy) 014 , which has a theoretical composition of 39.67. platinum. 0n the basis of its greater ionic character, Pt(dipy)3 (:11, should he the most soluble compound of the dipyridyl substituted 31 platinum (1V) chloride series, [Pt(dipy) Gig], [rt(dipy)z 612] 612, [Pt(dipy)3]c1‘. The red crystals obtained from the filtrate were considered to be Pt(dipy)3 €14. Efforts to increase the yields of this red compound led to experiments involving ethyl alcohol, acidic-aqueous solutions, and water-alcohol mixtures as the solvent for the reaction. None of the above methods increased the yield appreci- ably, and in all cases the yellow insoluble complex was the predominant compound formed. Further preparative attempts were based on a procedure used by 2. ll. Jaeger and J. A. van Dijk (l) in their synthesis of Rh(dipy)3 013-31120. This procedure involved the addition of anhydrous PtCl‘ to boiling 2,2 dipyridyl. This mixture was then heated on a water bath, after the addition of some water and ethyl alcohol, for several hours. Separation of the reaction mixture yielded a smell mount of a black residue and a dark red filtrate. Upon evaporation of this filtrate, the fibrous yellow compound began to form although the filtrate remained bright red in color. Recrystallization was carried out several times until the yellow complex was no longer formed during crystallisation. Several procedures were utilised for the crystallisation process in an effort to prevent the formation of the yellow complex. These were slow evaporation at room temperature, vacuum distillation and evaporation at higher temperatures. None of the above procedures prevented the formation of the yellow complex during crystallisation. The final product obtained from repeated recrystallisations consisted of a dark red, hygroscopic compound. 31 This substance was dissolved in.water and repeatedly extracted with ethyl other until the ether extract, upon evapora- tion, showed no traces of dipyridyl. Analysis of various preparations of this substance for platinum content did not give consistent results. The analysis ranged from 147. to 222 for platinum content. The theoretical com- position of the Pt(dipy)3 Cl‘ complex is 24.232 platinum. This inconsistency in analysis was thought to be due to dipyridyl hydrochloride impurities. further liquid-solid extraction was done utilising a soxhlat extractor and anhydrous other as the ex- tracting agent. continuous extrection*was carried out for eight to tanmweeks. Evaporation of the extracting solvent indicated a substance similar to dipyridyl or dipyridyl hydrochloride was being extracted. The final product was a hygroscopic, dark red, flat die-ood- shaped cryutelline compound. It was easily soluble in alcohol and insoluble in bensene or other. The absorption spectrun of an aqueous solution of this substance shows a‘wide absorption band in the visible region with a maxin- at 527 my. The absorption spectrum for the ultra-violet region between 340 mp and 240 m]! was more complex; however, absorption peaks were noted at 287 my, 297 my and a mall side bend at 320 my. The final yield of this substance was so small that analysis for platinum was not attempted. A.variation in the reaction procedure was tried in hopes that the red compound might be insoluble in molten dipyridyl in the absence of ethyl alcohol and water. if this were true, the 33 separation and crystallisation stops could be eliminated from the above procedure. Experiment revealed that the yellow'compound was formed almost immediately upon addition of PtCl‘ to molten dipyridyl but no trace of the red complex was detected even when the reaction was allowed to proceed for several days. However, upon the addition of ethyl alcohol and water the red substance appeared within a few hours. Another variation employed was the use of ethyl alcohol alone as a solvent in the reaction procedure in order to reduce the time for evaporation. Because of the low yields and the expense of the reagents these experiments were abandoned. Interest next centered upon possible preparations of the shmilar compounds Pt(py)6 C14 and Pt(phen)3 61g [where “py” is pyridine and "phen" is 1,10-phonanthrolind]. The procedure for preparation of the pyridine complex consisted of dissolving anhydrous PtCl“ in pyridine at a temperature slightly below boiling. immediately upon mixing a yellow, fibrous compound was formed. This compound use found to be extremely insoluble in water. Evaporation of the filtrate gave no indication of the presence of another compound. Preparation of Pt(phen)3 014 was attempted by the some pro- cedure used for the dipyridyl canplex. This method resulted in an insoluble brown residue and an orange colored filtrate. Evapora- tion of the filtrate yielded a.smsll amount of a waxy, orange compound. Repeated extraction with ethyl ether failed to remove enough of the 34 impurities, believed to be excess phenanthroline, to give well defined crystals. The results of these preparations cannot be considered conclusive; however, the following generalization might be made. Formation of tris(2,2-dipyridyl)platimnn (IV) chloride and related compounds is apparently deterred by the initial production of the acne .dipyridyl substituted compound. The extreme insolubility of this compound effectively removes it from solution and prevents further substitution fro. occurring. LITERATURE CITED 1. Jaeger, I. IL, and van Dijk, J. A., Free. Ace. Sci. kneterdam, 2e MCI. 'e P.. m Quin. Re Ce. Jo be (but. 3°C., 2-2.. 2322 (1950)e 3. Burstsll, r. 8., J. dun. Soc., 173 (1936). 11.111 11C'1111 S111£1 1 "111111111 111 MM: 5.111% A10 .11 .1 1. 3:1ENcg DEPARTAIIELT or C1‘ EH1:3TRY EAST LANSING, MICHIGAN CHEMISTRY LIBRARY Date Due Demco—293 MICHIGAN S'I'ME U1‘4E‘1’Q’ESETY OF AGRICULTURE AND APE-USO SC1ENCE DEPARTMENT OF CHEMISTRY EAST LANSING, MICHIGAN new?“ 111111111111 " c“, Groves, The effect of chloride on the rate of the thallium(I)-thallium(III) exchange reaction in 2.19f sulfuric acid. "7111111117 1711111111111 111117 1“