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Electronic Theses and Dissertations Theses, Dissertations, and Major Papers
1-1-1962
Studies in the thermal decomposition of metallic alkyls.
Michael G. Jacko University of Windsor
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Recommended Citation Jacko, Michael G., "Studies in the thermal decomposition of metallic alkyls." (1962). Electronic Theses and Dissertations. 6033. https://scholar.uwindsor.ca/etd/6033
This online database contains the full-text of PhD dissertations and Masters’ theses of University of Windsor students from 1954 forward. These documents are made available for personal study and research purposes only, in accordance with the Canadian Copyright Act and the Creative Commons license—CC BY-NC-ND (Attribution, Non-Commercial, No Derivative Works). Under this license, works must always be attributed to the copyright holder (original author), cannot be used for any commercial purposes, and may not be altered. Any other use would require the permission of the copyright holder. Students may inquire about withdrawing their dissertation and/or thesis from this database. For additional inquiries, please contact the repository administrator via email ([email protected]) or by telephone at 519-253-3000ext. 3208. THE PYROLYSIS OF TRIMETHYL GALLIUM
M . G . J ack o a n d S. J. W. P r ic e THE PYROLYSIS OF TRIMETHYL GALLIUM
M. G. J a c k o1 a n d S. J . W. P r ic e Department of Chemistry, Essex College, Assumption University of Windsor, Windsor, Ontario Received October 31, 1962
ABSTRACT The pyrolysis of trimethyl gallium has been studied in a toluene carrier flow system from 686° K to 983° K using total pressures from 6.1 mm to 31.1 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, and ethylene formed. The rate constants decline rapidly if the toluene-to-alkyl ratio is decreased below 45. Part of this decrease has been shown to result from the loss of methyl radicals as ethylbenzene, propane, propylene, and xylenes. In an unseasoned vessel, the decomposition is markedly dependent on surface conditions. In the unpacked conditioned vessel, the reaction is 94% homogeneous in the first bond region and 97% homogeneous in the second bond region. The decomposition occurs in two steps: Ga(CH3)3 -> Ga(CH3)s + CH3 [1] Ga(CHj>2 -> Ga(CHa) + CH3. [2] The analysis of a black solid from the reaction zone is consistent with the formation of (GaCH3)„. Both rate constants depend on the total pressure in the system, the dependence of ki being very slight. A least-squares analysis of the experimental results gives: log10 ki (sec-1) = 15.54- (59,500/2.303RT) log10 ki (sec'1) = 7.94—(35,410/2.303RT).
INTRODUCTION No previous kinetic studies of the thermal decomposition of trimethyl gallium have been reported. The heat of formation of trimethyl gallium has been obtained by the reaction of trimethyl gallium with iodine in benzene solution (1) and by the combustion of trimethyl gallium with oxygen (2). The mean gallium-carbon bond energies obtained from these studies are respectively 56.7±4 kcal/mole and 57.7±2 kcal/mole. In a recent review Long (3), using D(CH3—H) = 102.5 kcal/mole, has recommended a value of 57.5 kcal/mole. EXPERIMENTAL Materials (a) Trimethyl Gallium Trimethyl gallium was prepared by refluxing pure gallium with dimethyl mercury in an atmosphere of dry nitrogen, using mercuric chloride as catalyst (4). The fraction boiling at 56° C (uncorrected) was degassed by bulb-to-bulb distillation and stored under vacuum at —190° C. Melting point and vapor pressure data were in agreement with literature values (2). (b) Toluene (i) Toluene was prepared by the diazotization of o-toluidine followed by deamination with sodium hypo- phosphite. The organic layer was dried over anhydrous calcium chloride and fractionally distilled. The fraction boiling 109-110° C (uncorrected) was dried by refluxing over sodium under vacuum and degassed by bulb-to-bulb distillation. (ii) Toluene from sulphonic acid (Eastman Organic, X325) has been found to be as suitable as that des cribed above. It was dried by refluxing over sodium under vacuum and then degassed by bulb-to-bulb distillation. Apparatus and Procedure The experiments were carried out in a typical toluene carrier flow system in which the reaction zone was 195 cc. In the runs with the vessel packed with quartz tubing the surface area in the reaction zone was increased by a factor of 10 and its volume reduced to 145 cc. Pressures were measured using a mercury - di- octyl phthalate differ* ntial manometer designed to give a magnification of 10 to 1. The trimethyl gallium vapor was injected into the toluene stream through a capillary sealed to the barrel of a stopcock at the top 1Recipient of a National Research Council of Canada Studentship. Canadian Journal of Chemistry. Volume 41 (1903) 1560 JACKO AND PRICE: PYROLYSIS OF Ga(CH,)i 15G1 of the alkyl res voir. The alky! and toluene vessels were weighed at the end of each run to determine the amount of each used. In each experiment a pre-run of 4 to 6 minutes during which only toluene was passed was used to stabilize flow conditions. A similar post-run was used to remove all products from the reaction zone while conditions were still stabilized. In a few selected runs using the toluene from sulphonic acid, pre runs were extended to 30 minutes. During the first 25 minutes the gaseous products were collected and measured. The rate constants obtained agreed with those obtained from the decomposition of toluene from o-toluidine (5). An acetone - dry ice trap removed toluene, ethylbenzene, dibenzyl, and similar products. The remaining products were transferred by a diffusion pump to a Le Roy still at —160° C to remove traces of toluene and hydrocarbons higher than C2. The remaining H2, CH4, CJ1«, and C_>H4 were transferred past a non-return valve to a gas burette with the aid of a Toepler pump. After the gaseous mixture was measured, a sample was taken for chromatographic analysis. The chromatographic analyses were carried out using a 2-m silica gel column at 40° C with a flow rate of approximately 20 cc/min. Internal standards were run with each set of -nalyses so that peak heights could be used. In a few selected runs, the contents of the aceto ne-dry ice were analyzed using a 2-m di- isodecyl phthalate on diatomaceous earth column at 130° C with a flow rate of 28.5 cc/min. This method is sensitive to better than 0.0002 part ethylbenzene or xylenes in toluene. Analysis of a black solid rec vered from the reaction zone was carried out by admitting concentrated hydrochloric acid (12 N ) to an evacuated bulb containing a weighed sample. After 6 hours' digestion at 75° C, the bulb was cooled to —190° C. The non-condensable products were collected and measured and a sample taken for chromatographic analysis. The mixture in the flask was filtered through a weighed sintered- gl-iss crucible to determine the weight of the insoluble materials. The remaining solution was then twice evaporated to near dryness and then analyzed for gallium by titration with 0.01 M potassium ferrocyanide using 3,3'-dimethylnaphthidine in the presence of a trace of ferricyanide as indicator Hi).
RESULTS AND DISCUSSIONS Selected experimental results are given in Tables I and II. Analysis of the data indicates that the thermal decomposition of trimethyl gallium does 'ot occur by the simple release of three methyl radicals. It was found that even at 1075° K no more than two thirds of the theoretical quantity of methyl radicals could be accounted for. This is similar to the decomposition of trimethyl antimony (7) where the formation of (SbCH3)„ was indicated. To test for the possible formation of a similar gallium polymer, a black deposit scraped from the reaction zone was analyzed as previously described. The results of this analysis indicated: 80% gallium (I) oxide, 12% carbon, and 8% gallium methyl. The carbon is probably due to the decomposition of the carrier in the high-temperature runs. Since limited quantities of air ' ere admitted to the reaction vessel between certain runs to test for surface effects, the Ga20 could easily be formed from the reaction of 0 2 with (GaCH3)„. Subsequently r nalyses wert carried out on the contents of the acetone - dry ice trap and on the deposit in the furnace following each of a series of experiments. Under conditions such that less than one third of the theoretical yield of methyl radicals was observed, the gallium was found quantitatively in the acetone - dry ice trap. At temperatures above which two thirds decomposition occurred, the gallium was found quantitatively in the reaction vessel, as a thin, apparently non-metallic film. It therefore seems plausible that GaCH3 does not decompose but deposits in the reaction vessel as (GaCH,i)„. The following mechanism is proposed: Ga(CH3)3 -> Ga(CH3)2 + CH3 [1] Ga,CH3)2 -> Ga(CH3) + CH3 [2] »(GaCH3) -> (GaCH3)„ [3] CH3 + C6H6—CH3 -> C„H6— CH2 + CH4 [4] 2CH3 -> C2H8 [51 2C6H6—CH o - (C6H6—CH 2)2. [6] The small amounts of ethylene formed were assumed to arise from the reactions CH3 + C2H, -> C2Hr, + CH4 [7] C2Hs -> C2H4 + H. [8] CANADIAN JOURNAL OK CHKMISTRY. VOL. 41, 1903
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Hi approximately equal to moles CsH<. 1564 CANADIAN JOURNAL OF CHEMISTRY. VOL. 41. 1963 N O NO StSQ O O £5 ® 58 ■'** **■ cd £> C4 C O ^ C O C * i n © i m go co -*t< © to © -JcsaotoiMo©© INiOCO^CUOlNlNUO © O © © o ’ © © o ’ © goCO ooCO © 0 0© •*!< co © io - * ©O O o o O o C o© —l ( © N © oooo©oo JU —J © © © CO © CO © © CO M3 —* £ £ oooo©t>o ooao©oa V © ■,~o 00 U3 © U3 IN © 41 X £ 00©—I-coo© © > ur CO -S* - ^ © Tfl -#l © OOOOOOO .5 ’£ a> *c U3 -J 4) O O o O O O -H _ fc ca © —i ©© ©cj n < rt f IN © © CO© © (/]s fS O ® o > -S O O O O O O O ® ^ d d d ci d ao d "-H Cl Cl ** <0 f-H — * o c •5taO'-' £ c i u S E oooooooo 3 £ d d d d d d d d a 00«-»(MO®OOOOhWSiOM ® 2 ^ ^ ^ o *o |o . g —' S U H H H H C1! H ■'5 m rt HHHHrtOO® u o xooxoogooooooo £ s JACKO AND PRICE: PYROLYSIS OF Ga(CHi)i 1565 It was apparent from the analysis of the data that the second methyl radical was not released immediately after the first. The pattern of log ki/k£n shown in Fig. 1 indicates 2-5 20 2-2 AO /./ 13 /o o o ^ T Fig. 1. Arrhenius plot for the pyrolysis of trimethyl and dimethyl gallium and the reaction of methyl radicals with toluene. O log k\ # logkt/ki}12. Subscripts denote the number of runs averaged to obtain the given points. that the release of the first two methyl groups might be similar to the successive decom position of dimethyl zinc, first to zinc methyl and only at much higher temperatures to zinc plus a methyl radical (8). The detailed calculations of ki and ki have therefore been carried out as for the decomposition of dimethyl zinc, assuming that below 820° K the decomposition of dimethyl gallium is not an important source of methyl radicals. The mechanism further assumes that reaction [9] is unimportant. The following evidence CH3 + C6H6—CH2 — C6H6—CHoCHa [9] indicates the validity of this assumption under the experimental conditions used for most runs. First, values of ki obtained at 817° I< and 13.0 mm pressure using toluene-to-alkyl ratios between 45 and 120 show little variation. Similarly values of ki at 916° K and 13.0 mm using toluene-to-alkyl ratios between 45 and 120 show little variation. Previous experi ments and calculations (9) also indicate that under similar experimental conditions the loss of methyl radicals according to reaction [9] is negligible. However, as shown in Fig. 2, the value of log ki falls sharply when the toluene-to-alkyl ratio is decreased below 45. Values for ki are affected similarly. Additional gas chromatographic analyses have shown that the apparent falloff is due in part at least to the formation of propane, propylene, ethylbenzene, and xylenes. Analysis for butanes could not be made at present but these are probably also formed. The Arrhenius plots shown in Fig. 1 were plotted using ki's obtained using toluene-to- alkyl ratios of 45 to 120. The simple linear nature of these plots supports the method of calculation used. The curves may be represented by: logto ki (sec-1) = 15.54- (59,500/2.3031? T) logic ki (sec-1) = 7.94 — (35,410/2.3031? T) at 13.0 mm. No other plausible explanation of the results could be found. The values of k\ and ki were both extremely sensitive to the nature of the surface in the reaction zone. Admission of limited quantities of air to the conditioned vessel between 1566 CANADIAN JOURNAL OF CHEMISTRY. VOL. 41. 1903 /■a ■Ol 1.6 ZO 40 60 60 too IZjO C t o l/ Calk Fig. 2. Variation of k, with moles toluene to moles alkyl ratio using fixed toluene concentrations. O unpacked vessel at 817° K ; # packed vessel a t 801° K. runs resulted in approximately a 100% increase in ki and a 200% increase in k2 even after pumping over a 48-hour period. Approximately three runs were required to bring values of ki and k2 back to those normally observed in the conditioned vessels. Using a conditioned packed vessel with a surface-to-volume ratio 12 times that of the unpacked vessel gave values of ki 2.0 times and values of k21.4 times those observed in the unpacked conditioned vessel. It would therefore appear that in the conditioned unpacked vessel, both first and second bond ruptures are predominantly homogeneous processes with a 6% heterogeneous contribution in the first bond region and a 3% contribution in the second bond region. Both ki and k2 depend upon the total pressure in the system, although the dependence of k\ is very slight (Fig. 3). The dependence of k2 is similar to that observed for dimethyl to o 7 5 v» o — 7-6 - /O ZO 3 0 P r e s s u r e (mm) Fig. 3. Variation of ki and k2 with pressure. Subscripts denote the number of runs averaged to obtain the given point. mercury and dimethyl cadmium (9). Therefore, based solely on unimolecular pressure effects, the value of A 2 would be expected to be of the order 10n-1013 see-1. However, JACKO AND PRICE: PYROLYSIS OF Ga(CHj)i 1567 the observed A», 8.71 X107, is much lower than expected. This is presumably due to a change in multiplicity from triplet to singlet state as the second methyl radical is released from trimethyl gallium. The pressure dependence of log ki/kbU2 is shown in Fig. 4. The falloff with increasing 2-6 II o - i 0 20 30 P r e s s u r e Um) Fig. 4. Variation of k\/ks,m with pressure a t 817° K (first bond region) and 914° K (second bond region). Subscripts denote the number of runs averaged to obtain the given point. pressure is similar to that previously observed (7, 8, 9) and may be attributed to the third-body reqirements of reaction [5]. The experimental evidence although complex would indicate that the activation energies may be approximately related toZ?((CII3) 2Ga—CH3) and P((C H 3)Ga—CH3). Taking the total strength of the three gallium-carbon bonds equal to 172.4 kcal/mole (3) gives D{Ga—CH3) equal to 77.5 kcal/mole. ACKNOWLEDGMENT This work has been supported by a grant from the National Research Council of Canada. REFERENCES 1. P. A. F o w ell and C. T. M o rtim er . J. Chem. Soc. 3734 (1958). 2. L. H. L o n g and J. F. S ack m an . Trans. Faraday Soc. 54, 1797 (1958). 3. L. H. L o n g . Pure Appl. Chem. 2, 61 (1961). 4. G. E. C o ates . J. Chem. Soc. 2003 (1951). 5. S. J. P r ic e . Can. J. Chem. 40, 1310 (1962). 6. R. B e l c h e r , A. T. N u t t e n , and VV. I. S t e ph a n . J. Chem. Soc. 2438 (1952). 7. S. J. W. P r ic e and A. F. T rotman -D ic k e n so n . Trans. Faraday Soc. 54, 1630 (1958). 8. S. J. W. P r ic e and A. F. Trotman-Dickenson. Trans. Faraday Soc. 53, 1208 (1957). 9. S. J. W. P r ic e and A. F. T rotman -D ic k e n so n . Trans. Faraday Soc. 53, 937 (1957). THE PYROLYSIS OF TRIMETHYLINDIUM M. G. Jacko and S. J . W. P r i c e THE PYROLYSIS OF TRIMETHYLINDIUM M. G. Jacko1 and S. J . VV. P r i c e Department of Chemistry, University of Windsor, Windsor, Ontario Received December 12, 1963 ABSTRACT The oyrolysis of trimethylindium has been studied in a toluene carrier flow system from 550° K to 781° K using total pressures from 6.0 to 33.5 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, propane, and ethylbenzene formed and in a number of cases by direct indium analysis. The decomposition occurs in three steps: In(CHj)j -> In(CH,)2 + CHa [1] In(CHi)s —» In(CHj) + CH, [2] In (CH.,) —> In + CHc [3] At all temperatures reaction [2] follows rapidly after reaction [1], Reaction [3] occurs at a measurable rate only at temperatures sufficiently high that reactions [1] and [2] are com pleted in a very small fraction of the contact time. At lower temperatures the InCH, pro duced deposits in the reaction zone as a white film of (InCH,),,. Both ki and ki decline rapidly if the toluene-to-alkyl ratio is decrease'1 below 150. In an unseasoned vessel, the decomposition is markedly dependent on surface conditions. In the unpacked conditioned vessel the reaction is at least 89% homogeneous in the first bond region and 97% homogeneous in the third bond region. Both ki and ki depend on the total pressure in the system, the dependence of ki being very' slight. A least squares analysis of the experimental results gives: log,o*i (sec-1) = 15.72-(47,200/2.303RD logio *3 (sec-1) = 10.91-(38,700/2.303RD at 13.0 nun. E\ may be directly related to D[(CH,)2In—CHj]. A rough calculation based on unimolecular pressure effects indicates that £>[In—CH3] is probably about 2 kcal/mole greater than E 3. INTRODUCTION No previous kinetic studies of the thermal decomposition of trimethylindium have been reported. A study of the reaction of triisobutylindium with 1-decene at 150° C for 100 hours (1) yielded tridecylindium and 83% isobutylene. The tridecylindium broke down further to yield only 64% free indium metal plus 1/2 C Il 2= C H —C8Hi 7 and 3/2 C II3—CH2—C8Hn. The remaining indium was assumed to be in some polymeric form. A kinetic study of the thermal decomposition of trimethylgallium has been reported (2). The rate constants obtained were extremely sensitive to the nature of the surface in the reaction zone. After a series of runs, the reaction zone became conditioned and repro ducible results were obtained. The experimental results showed D\ — 59.5 kcal/mole and Di — 35.4 kcal/mole. From a knowledge of the total bond energies, Z>8 = 77.5 kcal/mole was calculated. The thermal decomposition of trimethylindium is expected to be similar to that of trimethylgallium and the other neighboring methyl metallic alkyls that have been studied (3, 4, 5). The mean metal-carbon bond dissociation energy in trimethylindium has not been reported. However, from available data on the methyl compounds of groups 115, II16, IV5, and Vb, a value for trimethylindium of E = 41±3 kcal/mole may be estimated. 1Recipient of a National Research Council of Canada Studentship. Canadian Journal of Chemistry. Volume 42 (1964) 1198 JACKO AND PRICE: PYROLYSIS OF TRIMETIIYLINDIYM 119!) EXPERIMENTAL Materials (a) Trimethylindium was prepared by refluxing indium metal with dimethylmcrcury in an atmosphere of dry nitrogen using mercuric chloride as catalyst (C). After 8 days the reaction flask was cooled to 0° C (vapor pressure of trimethylindium, 0.2 mm) and the unreacted dimethylmercury (vapor pressure, 17 mm) was distilled off. The crude trimethylindium was transferred to the main alkyl storage system where the remaining dimethylmercury was removed by repeated degassing at 0° C. The final product melted a t 89.5° C and gave vapor pressure measurements consistent with literature values (6). It was stored under its own vapor pressure at —190° C. (b) Toluene from sulphonic acid (Eastman Organic, X325) was dried by refluxing over sodium under vacuum and then degassed by bulb-to-bulb distillation. Apparatus and Procedure The experiments were carried out in a typical toluene carrier flow system in which the reaction zone was 195 cc. To test for surface effects the reaction vessel was packed with thin-walled quartz tubing of 2 mm O.D. The surface area in the reaction zone was increased by a factor of 10 and its volume reduced to 145 cc. Pressures were measured with a inercury-dioctylphthalate differential manometer designed to give a magni fication of 10 to 1. Trimethylindium was added to the carrier stream by a variable split-stream U-tube pickup system. Before a run, 0.1 to 0.2 gram of the alkyl was distilled from a weighed vessel into the U-tube and the vessel reweighed to determine the exact quantity used. The entire sample in the U-tube was used in the run. The period of alkyl injection was preceded by a 5- to 10-minute flow of toluene to stabilize flow conditions and was followed by a 5- to 10-minute flow of toluene to remove all volatile products from the reaction zone. An acetone - dry ice trap removed unreacted trimethylindium, toluene, ethylbenzene, dibenzyl, and similar products. The remaining products were transferred by a diffusion pump to a trap at —100° C (acetone-toluene sludge) to remove traces of toluene and hydrocarbons higher than C,. The remaining gaseous mixture was transferred past a non-return valve to a gas burette with the aid of a Tocpler pump. After the gaseous mixture was measured, a sample was taken for chromatographic analysis. Chromatographic analysis of the gaseous products was carried out using a 2-meter silica-gel column at 80° C with a helium flow rate of approximately 20 cc/min. The contents of the acetone-dry ice trap were analyzed using a 2-meter diisodecylphthalate on diatomaceous earth column at 130° C with a helium flow rate of 38.5 cc/min. This method is sensitive to better than 0.0002 parts ethylbenzene or xylenes in toluene. In the later stages, a Perkin-Elmer Model 800 gas chromatograph equipped with a 150-foot Golay column, 0.02 inch l.D. coated with polyfpropylene glycol) was used. This increased the sensitivity of the analyses to better than 0.000002 parts ethylbenzene in toluene. In 18 selected runs, the contents of the acetone - dry ice trap were analyzed for indium. Approximately 100 cc of concentrated hydrochloric acid (12 N) was added and the resultant mixture vigorously stirred and evaporated to 1 to 2 cc. The resulting indium trichloride solution was diluted to about 50 ml with distilled water, buffered with hexamethylenetetramine, and titrated with 0.02 M EDTA using xylenol orange as indicator (7). In 7 of these 18 runs, the indium content of the solid in the reaction zone was similarly analyzed. RESULTS AND DISCUSSION The experimental results are given in Tables I and II. They may be discussed in terms of the following mechanism: In(CH3)3 -> In(CH,)a + CH, [U ln(CH3)2 — In(CHj) + CH3 [21 In(CH3) —> In +CH, 13] *IIn(CHi)l - [In(CH3)]» 14] CHs + C,H r-CH 3 -> C6H6— CH2 + CH4 [a] 2CH3 -* C2H6 M followed by the usual reactions of the benzyl radicals to produce dibenzyl or ethylbenzene. The abstraction reaction [a] is a composite reaction proceeding mainly as written but with a small percentage of abstraction from the ring. The ethylene and hydrogen observed in small amounts result from the reactions: c h 3 + c 2h 6 -» c 2h 6 + c h 4 [51 C2H s -> C2H4 + H [6] H + C3Ht—CH3 -* CeH,r-CH2 +TL. 1200 TABLE IA ' S ( 5 c.= o ■« £ •«.S H w H NDA JUNL F HMITY VL 4, 1904 42, VOL. ISTRY. CHEM OF JOURNAL ANADIAN C e ft) —X ft) O a—. EU! a U ■e- u I © © © © © © © © © © © © © © © © © © © © © © © © © © © ~ 4 © O d C 0 C b i Q < e © C t 4 t ' ' - C 4 © < N C ' > C 3 l > » C O t Q t Q O S ) t f 3 Ccit^-co»coo©,*i* OOhC55Wf*OOClNiOift55OOHHOO?IOt0OOOOO« dOOGOi«l>©©©©©,«*fC^*OiOCCCOcO,'1 tf-MiftCCOOCOOOW^NW 'N©OCHflfitO^NWh'CS«Q»««MN^^00cg2NS©NrtOOOOWO^^ONMSgg ' t> I> O ^3------O O O M C C W C ^M ^^ -O C © © © © ©388388 wc'rtd d o dodo o* d o o' ddddddoddd d oo — OiaoOMN^ooosiftcOfroioCQCHtxc«OOHNrt®< 0^>0(NiO - CC — iflNCCNiMN^l < W « N W ^ W h h - o ^ O O O O O O O O < d © c o’ o’ d o* d o’ o’ o' o’ o’ o* o* o’ d d o’ o' o* o' d o' o* ONOOOO( S88oo8o888c ...... o’ d o’ o’ o’ o’ d © o’ o’ o’ o’ o’ o’ o’ o’ d o’ o’ d o’ o' o' o’ o ooooooooooooooooooooooooo OOM — © C-l M — l£ < S C O © OOi'NNWCJ' • -• •( ^ M W U 5 « N — ■ • —______©0000© ^— aC©< s w OTPifSOI^l^cO — OOMOIO^CJM—O — 2JOO J rl-^MN^Mff-W-HwOOOOOOOOOO CQ < doo'ddddo'cddoo'ddbddddddddd H OCMOO — MOWt^OOOOOOWQOQOCOOtfS^ — Ob-iOOOCCt^tOOOOt'-OO^ — t^OO lOO^’tMrtW^WHC'lWCCOOOHOOOOOOOONW ^ejswM^ooaag'jgts^ajgfiSSSO ode. co’dcddddddo’doddddddddd Mao*»*c‘ioccccci«©acc^fri©©,'+©©*t — — d o — *-< o’ o' d — — — d d o o ’d — *-< — o »-h — o n OOOOCOOOOOOOflWWCiflOOOOOOOO dddddddddddddddi^MdeoddMcoMd eCOO TABLE If % decomposition Trap Temp. - analysis k0 km (°K) Gas Metal (%> (sec-1) (sec' ‘) First bond region: 550 1.2 98.0 594 10.3 83.0 610 15.0 81.0 013 11.0 90.1 613 12.0 87.8 013 40.0 58.0 020* 19.7 13.3 85.7 0.219 0.138 023* 57.2 40.7 59.0 0.338 0.209 024* 50.3 30.9 03.7 0.292 0.183 633* 77.8 51.8 48.1 0.000 0.298 037* 64.8 40.5 53.2 0.533 0.320 644* 91.7 73.5 20.5 0.945 0.510 Third bond region: 684 45.3 1.2 697 03.1 2.5 720 72.8 0.9 720 57.9 3.9 729* 98.3 1.5 753 83.3 1.5 ♦Runs in an unconditioned vessel. The values of ka/k rl/2 given in Tables IA and IB have been calculated using the equation y /h 1 / 2 ______[moles CHj] 1___ Ra‘ r [moles C2H6+ C 2H4]1/2 F ^V ^toluene] where V — volume of reaction zone, and t — length of run. If in the decomposition of a compound of the type AI(CII:!)« we have •M(CH3)„ + y e n ,, [I] occurring over a temperature range T\ to 2\> while M CCHa),^ - AI(CH3)T O + zC H 3 [II] occurs appreciably only above T o , we shall have a number of factors which will influence the value of ka 'kTm. First, in a flow reaction, the temperature increases as the reaction zone is approached, therefore when the temperature in the reaction zone T x is above T o, reaction [I] will occur partly in the tube leading to the reaction zone and will be complete in some small fraction of this zone. This has a dual effect on ka/k rV2: (i) reaction [I] is occurring at an average temperature above T 2 but below T it and (ii) the volume over which reaction [I] occurs is no longer the total volume of the reaction zone. The net effect is to hold the apparent observed value of ka/k rin approximately constant as T increases. Actually, the net effect might be a slight decrease except for the fact that reaction [II] is occurring over the entire reaction zone at T s . Experimentally, for di- methylzinc, Zn(CF • 2 —> ZnCHj + CH3 [I] ZnCHj —> Zn + CHs [II] the ratio shows a slight decrease above (4). For trimethylgallium Ga(CH3)3 -> Ga(CH,)s + CH3 [I] Ga(CHj)3 -> Ga(CH3) + CH, [II] JACKO JXD PRICE: PYROLA'SIS OP TRIMETHYLINDIUM 1203 the ratio continues to rise slightly (2). In any case, a sharp break in the ka/kr1/2 curve is observed. The Arrhenius plot of ka'kr11- for the present work is shown in Fig. 1. In this case, the characteristic break occurs at 07% theoretical yield of methyl radicals indicating that below 670° K reaction [2] follows rapidly after reaction [I], but reaction [3] does not occur to any appreciable extent. Rate constants below this temperature ( ki) have therefore a./n /•« o U "4 tz Jz a 14 fS to 17 / • IOOO/T F ig . 1. Arrhenius plots for the pyrolysis of trimethyl- and methyl-indium and the reaction of methyl radicals with toluene. O rate constants based on gas analysis; % rate constants based on metal analysis; 0 log k„/k,w . Subscripts denote the number of runs averaged to obtain the given point. F ig . 2. Variation of ki and fc3 with pre- mre. Subscripts denote the number of runs averaged to obtain the given point. been calculated assuming that two methyl radicals are released for each trimethylindium undergoing reaction. Above (380° K all of the trimethylindium is converted to methyl- indium plus two methyl radicals in a very small fraction of the contact time. Rate con stants in this region ( k3) have therefore been calculated assuming that the fraction of the third bond ruptured is given by: (moles of methyl radicals) — (2 moles trimethylindium) moles of trimethylindium Although the break in the Arrhenius curve of ka/k rl/2 is indicative of the process outlined, independent tests have been made to verify the mechanism. (i) In 18 runs, the contents of the acetone - dry ice trap located at the outlet of the furnace were analyzed for indium. If reaction [4] is responsible for the removal of In(CHs), then above 670° K all the indium should be deposited in the reaction zone. Table II shows that over the entire third bond region only traces of indium reach the acetone - dry ice trap. Below this temperature the quantity of indium found in the trap was always in agreement with the proposed mechanism. (ii) In 7 of the 18 runs listed in Table II a clean pyrex vessel was used. In each of these seven runs the indium content of the reaction zone was analyzed. The values of ki calcu lated assuming moles of indium in the reaction zone equal the moles of trimethylindium decomposed are shown in Fig. 1. The agreement with ki values in a seasoned vessel calcu lated assuming two methyl radicals released for each trimethylindium decomposed is excellent. 1204 CANADIAN JOURNAL O F CHEM ISTRY. VOL. 42, 1901 (iii) The rate constants for the reaction in a clean vessel based on gas analysis lie above the Arrhenius curve. The difference in extent of reaction based on metal analysis is a result of reaction on the unconditioned surface. The most probable surface reactions consistent with the experimental results are the surface decomposition of methylindium to give indium metal plus a methyl radical and the surface decomposition of trimethyl indium. The first of these reactions leads to a decrease in the quantity of (InCH 3)„ deposited in the reaction zone. Hence in an experiment in an unconditioned vessel in which 1.0 millimole of methylindium would have been deposited in the reaction zone in a con ditioned vessel, addition of bromine vapor to the hot reaction vessel (637° K) while still under vacuum produced only 0.34 millimole of hydrogen bromide and a quantity of polymethylene qualitatively in agreement with the reaction 2«Br» + (InCHa)„ — wlnBr, + »(CHS) + nHBr followed by the polymerization of the methylene radicals in cooler regions of the reaction vessel. The 0.66 millimole of methylindium apparently lost by surface decomposition was in good agreement with the additional methyl radicals detected in the gas analysis (0.58 millimole). Starting with a clean vessel, both ki and k3 decrease over several runs to a fixed mini mum value in what is subsequently called a conditioned vessel. If air is admitted to the reaction vessel between runs, an additional two to three runs are required to recondition the surface of the reaction vessel. The percentage of heterogeneous reaction in the con ditioned vessel was estimated by carrying out a series of runs in a packed vessel with a surface-to-volume ratio 12 times that of the unpacked vessel. Because of the large surface area, complete conditioning was probably not obtained, but after a series of runs ki was reduced to about 2.2 times its value in the unpacked vessel and k3 to about 1.3 times its value in the unpacked vessel. Therefore, in the unpacked vessel used in this work, the reaction is at least 89% homogeneous in the first bond region and at least 97% homo geneous in the third bond region. Both ki and k3 depend on the total pressure in the system, although the dependence of ki is very slight (Fig. 2). The slight pressure dependence of ki is similar to th at observed in the decomposition of trimethylgallium (2). As shown in Fig. 3, the pressure dependence U - * o 01 M M <0 L o s Pfmm) F ig. 3. Comparison of the effect of pressure on the rate of thermal decomposition of InCH3 and ZnCHj. of the decomposition of methylindium is somewhat less than that of methylzinc (4). This is presumably due to the large temperature difference at which these decompositions occur. The pressure dependence of ka/krm is shown in F'ig. 4. The fall-off with increasing JACKO AND PRICE: PYROLYSIS OF TRIMETHYLINDIUM 1205 i r- /8 'bo n6to°K /7 ~ \ t-6 0 ^ 0 AS Z 2 T -T *0°K 21 X >• 29 Q 2 0 ~ -d' A*- 4 _i_ _L 10 2 0 3 0 no too too ooo P m SSV l?£ (mm) CtCL/c ALk F ig. 4. Variation of ka/ k , ln with pressure at 610° K (first bond region) and 744° K (third bond region). Subscripts denote the number of runs averaged to obtain the given point. Fig. 5. Variation of k i with the ratio of moles toluene to moles alkyl using fixed toluene concentrations. pressure is similar to that previously observed (2-5) and may be attributed to the third body requirements of the methyl radical recombination reaction. As shown in Fig. 5, the value of ki falls sharply when the toluene-to-alkyl ratio is de creased below 150. Values for k3 are similarly affected. The Arrhenius curves shown in Fig. 1 were therefore plotted using only rate constants obtained in runs where the toluene- to-alkyl ratio was greater than 150. At 13.0 mm, the curves may be represented by: log,0 ki (sec-1) = 15.72-(47,200/2.30.3R7'), logio &3 (sec-1) = 10.91 — (38,700/2.303i?r). The experimental evidence indicates that the activation energies may be approximately related to the bond strengths, although a rough estimate based on unimolecular pressure effects indicated that Dz is about 2 kcal/mole greater than Ez. Thus -D[(CH3)2In— CH3] equals 47.2 kcal/mole and Z)[In—CH3] equals 40.7 kcal/mole. The mean bond energy in trimethylindium is not known. However, comparison of neighboring methyl metallic alkyls indicate that E{ln —CH3) in trimethylindium is probably 41±3 kcal/mole. Allowing limits of error of ±1 kcal/mole in Dj and D3 would give Z)[CH3In—CH3] equal to 35±5 kcal/mole, a value consistent with the proposed mechanism. ACKNOWLEDGMENTS This work has been supported by a grant from the National Research Council of Canada. REFERENCES 1. J. J. E i s c h . J. Am. Chem. Soc. 84 , 3605 (1962). 2. M. G. J a c k o and S. J. W. P r ic e . Can. J. Cheni. 41, 1560 (1963). 3. S. J. W. P r i c e and A. F. Trotman-Dickenson. Trans. Faraday Soc. 54, 1630 (1958). 4. S. J. W. P r i c .nd A. F. Trotman-Dickenson. Trans. Faraday Soc. 53, 1208 (1957). 5. S. J. W. P r i c e and A. F. Trotman-Dickenson. Trans. Faraday Soc. 53, 937 (1957). 6. L. M. D e n n is , R. W. W o r k , F. G. R ockow , and E. M. C harm ot . J. Am. Chem. Soc. 56, 1047 (1934). 7. J. K in n u n e n and B. W en n estr a n d . Chemist-Analyst, 46, 92 (1957). STUDIES IN THE THERMAL DECOMPOSITION OF METALLIC ALKYLS BY MICHAEL G. JACKO A Thesis Submitted to the Faculty of Graduate Studies through the Department of Chemistry In Partial Fulfillment of the Requirements fo r the Degree of Doctor of Philosophy at the University of Windsor Windsor, Ontario 196M- UMI Number: DC52596 UMI ® UMI Microform DC52596 Copyright 2007 by ProQuest Information and Learning Company. Ali rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 THIS THESIS HAS BEEN EXAMINED AND APPROVED BYl L ABSTRACT The metal-carbon bond strengths for some of the metals in Groups lib , IVb, and Vb have been determined. The object of this work was to study the metal-carbon bond strengths of the Group Illb metals - gallium, Indium, and thallium. The thermal decompositions of trimethylgallium, tri methylindium, and trimethylthalllum have been studied In a toluene carrier gas flow system. The methyl derivatives of these metals were chosen so that the reactions of the radi cals released on decomposition might be as simple as pos sible. The overall progress of the decompositions was followed by measuring the amount of methane, ethane, ethy lene, propane, and ethylbenzene formed, and In a number of cases by direct metal analysis. In an unseasoned vessel, the thermal decompositions were dependent on the surface conditions. In an unpacked conditioned vessel, trimethylgallium was 9$ heterogeneous, dimethylgallium trimethylindium 10$, methylindium 3%, and trimethylthalllum lW$. All rate constants depended on the total pressure In the system. The pressure dependence for the decompositions of the trimethyls was slight, but increased for the dimethyl and monomethyl forms. The break in the curve of the Arrhenius plot of kaA ^ 1 1 indicated consecutive reactions; the second bond was not immediately released after the first if this break occurred at 33$ theoretical yield of methyl radicals (as in tri methylgallium); the third bond was not immediately re leased after the second if this break occurred at 67$ theo retical yield of methyl radicals (as in trimethylindium); no break indicated th a t the second and th ird bonds ruptured rapidly after the first. Independent tests were carried out to verify these mechanisms. From theoretical considerations, It was shown that the experimental activation energy may be approximately related to the bond strengths. In the thermal decomposition of trimethylgallium, the f i r s t two metal-carbon bond energies were determined d ir ectly and the third was determined by differences D/-(CH3)20a-CH3_7 5 59.5 kcal/mole DZ"(CH3)Ga-CH3_7 = 37.2 kcal/mole Z"Oa-CH3-7 a 75.8 kcal/mole In the thermal decomposition of trimethylindium, the f i r s t and th ird metal-carbon bonds were determined d ire c tly and the second was determined by differences D/7*(CH3^In-CH^^7 = ^7.2 kcal/mole DZ“(CH3)In-CH3-7 = 27.b kcal/mole DZ"*In-CH3_7 = '*■0.0 kcal/mole In the thermal decomposition of trimethylthalllum, only the first bond could be determined: D/-(CH3)2Tl-CH3-7 * 2 6 kcal/mole i l l ACKNOWLEDGEMENTS I would like to take th is oppor tunity to acknowledge with gratitude the direction of Dr. S.J.W. Price, who by h is patience and guidance greatly en hanced the quality of th is work. I would also lik e to thank the National Research Council of Canada for the two Studentships th a t were awarded to me during the course of this work. TABLE OF CONTENTS ABSTRACT ...... ACKNOWLEDGEMENTS . . . . LIST OF TABLES ...... LIST OF ILLUSTRATIONS TABLE QF NOMENCLATURE Chapter I . INTRODUCTION General Introductory Remarks ...... Some Previous Studies by the Toluene Carrier Technique...... Introduction to the Present Research.• I I . THEORETICAL CONSIDERATIONS Theory of the Metal-Carbon Bond ...... Properties of Metallic A lkyls....••••• The Croup Illb M etals...... M etallic Alkyls of Croup I l l b ...... Mean Bond Energies by Calorlmetrlc Methods...... Bond Dissociation Energies by the Kinetic Method...... Pressure Dependence of Bond Dissocia tion Energies...... The Toluene Carrier Cas Technique ...... K inetics of Unlmolecular Decomposi tio n s ...... •••• Kinetics of Methyl Extraction...... I I I . EXPERIMENTAL Preparation of Materials Chapter Page ApparatusA pparatus...... kg Experimental Technique, IV. EXPERIMENTAL RESULTS The Pyrolysis of Trlmethylgalliunu.... 58 The Pyrolysis of Trlmethylindium.••••. 76 The Pyrolysis of Trimethylthallium.••• 91 V. DISCUSSION Reaction of Methyl Radicals with Toluene. • • • 106 The Toluene Carrier Technique...... 109 The Pyrolysis of Trlmethylgalllum..... 110 The Pyrolysis of Triaethylindium. 112 The Pyrolysis of Trimethylthallium. •• • 113 Suggestions for Further Work...... 11* BIBLIOGRAPHY...... 117 VITA AUCTORIS...... 120 v i LIST OF TABLES Tables Page 1. The Pyrolysis of Dimethylgalllum ...... 59 2. The Pyrolysis of Trlmethylgalllum ...... 60 3* The Pyrolysis of Dimethylgalllum and Trlmethylgalllum (Packed Vessel Runs) •••• 61 *f. Variation of k with ctol/Calk ••••••••*••• 68 5# Pressure Dependence of Hetal Dimethyls ••• 73 6 . The Pyrolysis of Methyllndlum ...... 77 7* The Pyrolysis of Trlmethylindium 78 8 . The Pyrolysis of Methyllndlum and Trl methylindium (Packed Vessel Runs)••••••••• 79 9* Runs with Indium Analyses 82 10* Variation of k with ctol/Calk ••••••#••••• 90 11. The Pyrolysis of Trimethylthallium (In a Unpacked Unconditioned Vessel) ...... 92 12. The Pyrolysis of Trimethylthallium (In a Packed Unconditioned Vessel) ...... 93 13. The Pyrolysis of Trimethylthallium (In a Unpacked Conditioned Vessel) ...... 9*+ 1^. The Pyrolysis of Trimethylthallium (In a Packed Conditioned Vessel) ...... 96 15. Runs with Thallium Analyses ...... 99 16. Metal-Methyl Bond Strengths ...... 116 v ii LIST OF ILLUSTRATIONS Figure Page 1. Formation of the sp3 Hybrid O rbital .••••• 12 2. Potential Energy Curve for a Unimolecular Decomposition into two Radicals ...... 29 3* Schematic Diagram of the Toluene Carrier Flow System used in th is W ork ...... 1*6 k. Injection System for a Volatile Metallic Alkyl ...... 1*9 5* Pick-up System for Metallic Alkyls of Low Volatility ...... 50 6. Placement of Heating Windings in the Furnace Construction ...... »« 51 7* A Typical Temperature Profile ...... 51 8 . Arrhenius Plots of Rate Constants for the Decomposition of Trlmethylgalllum and Di- methylgalliuin and the Reaction of Methyl Radicals with Toluene 65 9. Variation of Rate Constants with the Molar Ratio of Toluene-to-Alkyl ...... 69 10. Variation of Rate Constants with Pressure for Trlmethylgalllum and Dimethylgalllum • 72 11. Variation of Rate Constants of Various Dimethyl Metals with Pressure ...... 7*t 12. Variation of kaAr* with Pressure ...... 75 13. Arrhenius Plots for the Decomposition of Methyllndlum and Trlmethylindium and the Reaction of Methyl Radicals with Toluene.• 81 ll*. Variation of Rate Constants with Pressure for Trimethyllndium and Methyllndlum ••••• 86 v i i i 15. Variation of Rate Constant with Pressure for Methyl M e ta ls ...... ••.••.••••••••• 87 16. Variation of kaAr^ Pressure ...... 88 17. Variation of Rate Constants with Molar Ratio of Toluene-to-Alkyl 89 18. Arrhenius Plot for the Reaction of Methyl Radicals with Toluene ...... 98 19. Arrhenius Plots for the Decomposition of Trimethylthallium ...... »•...... 101 20. Variation of ka/kr^ wlth Pressure •••.•••• 10*+ 21. Variation of Rate Constant with Pressure for Trimethylthallium ...... 10*t 22. Arrhenius Plot for the Reaction of Methyl Radicals with Toluene ...... 108 iz TABLE OF NOMENCLATURE A ...... Pre-Exponential Factor of the Arrhenius Equation A,B,C .... Moments of Inertia of a Molecule D . Bond Dissociation Energy E Arrhenius Activation Energy E0 Arrhenius Activation Energy at the high Pressure Limit ff ...... Mean Bond Energy h Planck's Constant K . Transmission Coefficient kf Boltzmann's Constant k ...... Rate Constant koo...... Rate Constant a t the High Pressure Limit m Mass of a Moleoule ...... i Number of Atoms in a Molecule n' Number of Effective Osolllators in a Moleoule R ...... Gas Constant Rl ...... Free Radical Group T ...... Absolute Temperature A Hf ••••• Standard Heat of Formation at 25° C . Vibrational Frequenoy 9 ...... Parameter Related to the Amplitude Factor o ...... Symmetry Number x CHAPTER I INTRODUCTION General In tro d u cto ry Remarks The dissociation energy, dZ~r 1- r 2J» of a bond R 1-R2 is the change in energy at the absolute zero in the ideal gas state, B0 > for the reactions R]aR2 — *■ Ri 4* R 2 with the products being in th e ir ground sta te . The bond dissociation energy is the most direct measure of the strength of a bond, and therefore of the stability of the chemical combination between the two atoms or radicals from which it is formed. Theoretical Chemistry is concerned with chemical information from general principles, ulti mately from physical laws governing the behaviour of nuclei and electrons. Energy quantities are perhaps the most accessible numerical quantities we can hope to calculate for chemical systems, and it could be maintained that the most specific energy quantities are dissociation energies. The fact that it has been possible to account qualitatively for the chemical binding and quantitatively for the dissoci ation energies of hydrogen and other simple molecules is important evidence that Theoretical Chemistry is on the right path. The present objective is to expand Theoretical Chemistry. To have reliable experimental values of bond 2 dissociation energies is to have a useful touchstone to test our theoretical ideas on chemical binding. More specifically, the objective of the present research is to give reliable experimental values of dissociation energies for some metal-carbon bonds. Bond dissociation energies can in general be deter mined in a variety of methods, among the most common are the followings thermal equilibrium methods, electron im pact methods, spectroscopic methods, photochemical methods, and kinetic methods (static and flow systems). However, the methods that can be employed satisfactorily to deter mine metal-carbon bond dissociation energies in metallic alkyls are rather limited. The radicals produced in the initial dissociation are too reactive to allow the use of any thermal equilibrium method. Although spectroscopic methods are capable of giving the most accurate values for dissociation energies of simple molecules, they cannot be used for polyatomic metallic alkyls because of the complex ity of their spectra. Electron impact methods give only the upper lim it of the dissociation energy and are compli cated due to the large number of atoms present in the metallic alkyl molecule. The determination of bond dissoci ation energies by photochemical methods are reliable only if the mechanism of absorption of radiation and the subse quent decomposition can be established^ the result will be a maximum bond dissociation energy. Mean bond energies of m etallic alkyls can be determined by caloriraetric methods. Calorimetric methods include the measurements of heats of hydolysis, heats of halogenatlon, combustion in static-bomb calorimeters, and combustion in rotatlng-bomb calorimeters. Activation energies from the thermal decomposition of metallic alkyls have been determined using both static and flow systems. If the process observed experimentally is a unlmolecular decomposition producing two radicals whose energy for recombination is small, the experimental acti vation energy determined will be a good approximation to the bond dissociation energy. The complexity of reactions in s ta tic systems is such th at unambiguous in terp etatio n of the result is almost impossible. The interpetation of re sults from experiments in flow systems has been much more satisfac to ry . Hydrogen was the first carrier used in flow systems to act as a radical scavenger and could be used over a very long temperature range) however the separation of the gaseous products from the hydrogen was dlffioult and required measurements by difference. The toluene carrier flow system, although limited for very high temperature work, offers the most satisfac to ry method fo r reducing the complexity of the reaction and gives satisfactory results* Soma Previous Studies bv the Toluene Carrier Technique The metal-carbon bond strengths of the Group IZb metals zinc, cadmium, and mercury have been determined by the toluene carrier technique (a kinetic method) and the mean metal-carbon bond energies have been determined by calorimetry* The correlation of the results of these two methods is best exemplified by comparing the total bond energies obtained by the thermal decomposition of dimethyl- zinc £“lj and the mean bond energy obtained from studies of the heat of reaction of dimethylzlnc with water in ether solution f2jm From the heat of formation of dimethylzlnc, the bond strengths D^“CI^Zn-CH^ and DZ"” Zn-CRyJ were calculated equal to 82.9 kcal/mole (assuming Q C V R y & J s 102*5 kcal per mole), and thus E s ^1*5 kcal/mole. The thermal de composition of dimethylzlnc in the toluene carrier flow system proceeds by the following mechanisms Zn(CH3 ) 2 — ► Zn(CH3) + CH3 (1) Zn(CH3) — Zn + CH 3 (2) Reaction (2) occurs at much higher temperatures than reac tion ( 1 ) such that at high temperature reaction ( 1 ) occurs in a very small fraction of the contact time and reaction (2) can readily be determined* If the activation energies of these two reactions are equated to the metal-carbon bond strengths, Di s V 7. 2 , D2 s 35» and Di plus D2 equal 82.2 kcal/mole. D2 has a probable error of about U- kcal/mjle due to the large decomposition of the carrier. Both steps of the decomposition have rate constants that are markedly dependent on the total pressure in the system. The apparent activation energy of a unimolecular reaction is a function of the pressure at which it is 5 determined if the reaction itself is a function of pressure* Taking pressure dependency into consideration, both and D2 are probably 2 kcal/mole higher than the experimental activation energies; consequently the agreement between the k in etic and calorim etric methods is meaninglessly good. However, this agreement indicates that when dimethylzinc decomposes completely, the zinc atom is released in the ground state. In the thermal decomposition of dimethylcadmium, the mechanism is d ifferen t from th at of dimethylzinc in th at the second methyl radical was released immediately after the first, and Its rate could not be measured klnetically* From the heat of formation of dimethylcadmium obtained by calorim etric methods, plus D^Cd-CH^JP «Qual 66*8 kcal/mole The experimental activation energy was related to the first metal-carbon bond strength such that Di = ^ 5.8 kcal/mole at 16 mm (pressure dependent re gion) Dj, is probably about 2 kcal/mole larger than the experimental activation energy, and thus &2 may be assigned a value equal to 19 kcal/mole* From thermochemistry, the two metal-carbon bonds of dimethylmercury have a combined strength of 57*3 kcal/tnole c %j . However, the precise mechanism and assignment of energies to each individual bond is apparently lnoonolusive* can probably be assigned a minimum value of 50 kcal/mole* The metal-carbon bond strengths of the Group Vb metals bismuth, antimony, and arsenic have been determined by 6 calorimetry while only the raetal-carbon bonds of bismuth and antimony have been studied by the toluene carrier tech nique. The observed thermal decomposition of triraethylbismuth was straightforward in runs where the observed decomposition was close to 100#, the measured amounts of methane and ethane produced were in agreement with the anal ysis of the undecomposed m etallic alk y l. Thus three methyl radicals were released each time a trimethylbismuth molecule decomposed and the following mechanism was proposed) Bi(CH3)3 - ► Bi(CH3)2 + CH3 (3) b i(c h 3) 2------bi(ch3) + ch 3 (V) Bi(CH3)------Bi + CH3 (5) where both reactions GO and ( 5) proceed immediately after reaction (3). The experimental activation energy was re lated to the strength of the first metal-carbon bond of tri- methylbismuth D^f’(CH 3)2®i-CH3_7 * ^ * 0 kcal/taole at 16 mm (pressure Independent region). From the heat of formation of trimethylbismuth the sum of the three metal-oarbon bond strengths was lOl.lf kcal/mole (if D^"CH 3-HL7 ■ 102.5 kcal/mole). The value for the sum (D 2 + D3) of the seoond and third metal-carbon bond strengths was 57*8 kcal/mole. On the other hand, the observed thermal decomposition of trimethylantlmony was not simple *t higher decom positions gaseous products corresponding to 7k% decomposi tion were produced while amounts of antimony corresponding to 98 £ decomposition were deposited in the reaction zone. 7 This discrepancy was not due to the formation of substances such as hydrogen, ethylene, or propylene, for negligible quantities of these gases were produced. The apparent loss of methyl radicals was most simply interpeted by assuming that a polymer of the type (SbCH^n was produced. Neverthe less, for the purposes of further discussion it was conven ient to assume that for each trimethylantimony molecule undergoing decomposition three methyl radicals were released. The first order rate constant based on gas analysis kg approached the rate constant based on metal analysis kra at low decompositions ( 0.179 and 0. 215, respectively) but diverged at high decompositions ( 1.00 and 3 .I 6frespectively). This corresponds to 91% agreement (based on percent decom position) at low decompositions and only 75% agreement at high decompositions. The activation energies from the Arrhenius equations derived from the metal and gas analyses are 57*0 and 53*5 kcal/mole,respectively. The activation energy bused on the metal analyses was assumed to be the more probable estim ate fo r the first metal-carbon bond strength of trimethylanti- mony, D^CI^JaSb-CHjJP * 57.0 kcal/mole. From the heat of combustion of trimethylantimony a value of 1^9 #1 kcal/mole for the sum of the three metal-carbon bonds of trimethylantimony was found. Thus 3S s 1+9.7 kcal/mole and the first metal-carbon bond strength equal to 57*0 kcal/mole seems reasonable. From the heat of formation of trimethylarsenic, the 8 total strength of the three metal-carbon bonds equals kcal/mole £~9j* Since the pyrolysis of trimethylantimony was so complex even when studied by the toluene carrie r technique, it was difficult to believe that the pyrolysis of trimethylarsenlc in a static system was straightforward* Probably little reliance could be placed on the suggestion that the overall activation energy of kcal/mole ob served by Ayscough and Emeleus £*10 J was equal to the strength of the first metal-carbon bond of trimethylarsenlc* Of the Group IVb m etals, a tin compound, dim ethyltln dichloride, is the only compound of this group that has been studied by the toluene carrier technique. The decomposition of this compound was straightforward and the products were tin dichloride plus two methyl radicals* The experimental activation energy was equated to the strength of the first metal-carbon bond giving D ^C l^^Sn-C H jJP * 56*1 kcal/mole a t 16 mm (pressure independent region) This bond dissociation energy is close to but greater than the mean bond energy of the metal-oarbon bonds in tetramethyltin which have been reported to be 53*5 koal/taole £ ^ 7 * I t is expeoted that the strength of the first metal-oarbon bond in tetramethyltin will be greater than 53#5 but less than 56*1 koal/mole. This is predioted by the observation that the redistribution of stannlo halides with stannlo alkyls was exothermic. The metal-oarbon bonds in alkyl merourlo halides were found to be considerably stronger than the bonds in the corresponding dlalkyls C&J as in the series: D£ ClHg-CH'}^/ = 63 kcal/mole BrHg-CH^J/ - 60.7 kcal/mole V £ " IHg-CHs J s 59 .O kcal/m ole D/“CH3Hg-CH3-7 = <57.3 kcal/mole. Introduction to the Present Research Comparatively l i t t l e was known about th e m etal-carbon bond strengths in the alkyls of the Group Illb metals gal lium, indium, and thallium. The object of the present re search has been the determination of the strengths of the metal-carbon bonds of trimethylgallium, trlmethylindium, and trimethylthallium. The trimethyls of these metals were so chosen because the bond ruptures should involve the simple release of methyl radicals. No previous kinetic studies of the thermal decomposi tion of trimethylgallium, trlmethylindium, or trimethyl thallium have been reported. The heat of formation of trimethylgallium has been obtained by the reaction of trimethylgallium with iodine in benzene solution r u 7 , and by the heat of combustion of trimethylgallium with oxygen m a static-bomb calori m eter r & j . The mean gallium-carbon bond energies ob tained by these studies were 56.7 - *+ kcal/mole and 57.7 £ 2 kcal/mole, respectively. In a recent review Long 15iy, using DZrci^-Hy * 102.5 kcal/mole, has recommended a value of 57*5 kcal/mole. 10 A study of the reaction of tri-isobutylindium with 1-decene at 150° C for 100 hours yielded tridecylindium and 83% isobutylene £ " 16_7. The tridecylindium broke down further to yield only (h% free indium metal plus one-half mole CH2=CH-CgH^7 and three-halves moles CH^d^-CgH^# The remaining indium was assumed to be in some polymeric form. The mean m etal-carbon bond energy of trimethylindium has not been reported. However, from the available data on the metal methyl compounds of Groups lib, Illb, XVb, and Vb, a value for trimethylindium of E ■ kl £ 3 kcal/mole was estimated* From incomplete studies on the heat of reaction of trimethylindium with bromine in chloroform solution, the mean indium-carbon bond strength indicated by these studies Is 38*2 kcal/mole CllJ* This tentative experi mental value will be used in further oaloulatlons in this work# CHAPTER I I THEORETICAL CONSIDERATIONS Theory of the Metal-Carbon Bond The polarity or degree of ionic character of a bond not only influences the physical properties of the compound in accordance with the well-known characteristics of ionic and covalent compounds, but also markedly influences the chemical reactivity of the compound. In general, bond partners carry a difference of electrical charge relative to each other and this serves as a dipole that attracts and orientates neighbouring reagents. The intensity of attrac tion may be expected to influence the rate of reaction, and the direction of orientation will govern the products that are formed. The carbon atom with its 2s^ electrons and 2p^ elec trons in the outermost orbitals available for chemical binding, does not ordinarily employ them in these particular forms in chemical reactions. Instead, these four electrons in three orbitals (each p electron is in a separate orbital) are redistributed into four new hybrid orbitals, all equi valent in energy and tetrahedrally distributed in space; the s electrons are not distinguisable from the p electrons as would be expected because of the 2s^2p^ distribution, nor do we find two undirected s orbitals and two 90° p 11 12 orbitals. The hybrid situation comes about by the ’pro motion' of one of the 2s electrons to the third p orbital (unoccupied until now), followed by the Interaction of the remaining s orbital with the three p orbitals to produce the sp3 hybrid as shown In Fig. 1. This figure shows a schematic representation of the Interaction of wave-mech anical expressions governing electron probability; the net effect Is a lengthening and enlargement of one lobe of the p orbital and the marked shrinkage of the other. The re sulting four elongated lobes are directed outwards from the origin towards the oorners of a tetrahedron. If these four lobes overlap with the spherical orbitals of four hydrogen atoms, bonding re su lts and the tetrah ed ral moleoule methane Is produced. 0 * 00-0 5 p h ybrid Fig. It Formation of an sp3 Hybrid Orbital. 13 The promotion of an s electron to a higher energy p orbital in order to begin this process requires energy, but the energy is recovered in the process of chemical combina tion to form the stable tetrahedral product. The chief advantage of a hybridized atomic orbital is its high direc tional character, which according to the principle of maxi mum overlapping should yield a stronger bond. Certain general features of bond strengths follow from such considerations. In the first place, s bonds are almost al ways weak (excluding H 2 because of the inherent stability due to a completed orbital). This is because two similar s orbitals on adjacent atoms cannot possibly overlap to any great degree because of the spherically symmetrical distri bution of their charge. Such bonds are weaker than p bonds, where the directional character allows considerable overlap. Both of these should be weaker than the sp3 hybrid where the overlap is very great. Interesting examples of these rules are the molecules Li 2 , F2 » and c 2 (as *n 62** 5) where the bond energies are 26, 35, and 80 kcal/mole^ respectively. The other Group IVb elements, silicon, germanium, tin, and lead form tetrahedral sp3 hybrids in the same way. The above advantages of bonding with such orbitals accrue to these metals, and an extensive organic chemistry for each of them is found based on tetrahedral compounds of the type RI4.M, In the heavier elements there can be the withdrawal of the s electrons as an inert pair and the use of only the p electrons to form nctal alkyls of the type R 2M. The Ik compounds formed are unstable. The marked Increase in stability of Rl+M over R 2M emphasizes the benefits of hybrid izatio n . Looking fu rth er, metals outside the fourth group may form sp hybrid orbitals, but necessarily of some type other than sp3. The Group Illb metals gallium, Indium, and thallium, with their outermost electronic configuration of ns 2np^ may promote one of the s electrons to the p level and form three trig o n al sp 2 hybrid orbitals leading to volatile metallic alkyls of the type R 3M* In Group lib , there is the promotion of one of the s electrons to the p level with the formation of two linear sp hybrid orbitals leading to volatile metallic alkyls of the type R 2M. Ele ments in Group Vb, with single electrons in each p orbital cannot improve m atters by hybridization and are content with metallic alkyls of the type R 3M, where the s electrons probably remain as an Inert pair. In the Group Vlb elements, the fourth p electron added goes Into an orbital with one of the other p electrons; consequently matters cannot be Im proved by hybridization and metallic alkyls of the type R 2M are formed, the s electrons and the paired p electrons forming two Inert pairs. If the metal-carbon bond Is represented by M-C, we may designate relative polarity by indicating fractions of elec tro n ic charge in the following manner! 8 ®m-c S® The electronic cloud constituting the bond Is not equidistant 1 5 between the nuclei, but is shifted towards the carbon atom because of its electronegativity. A methyl group is rather positive relative to the hypo thetical free carbon atom, for in a methyl group the carbon bears three hydrogen atoms which are considerably more elec tropositive than the carbon itself. In this way the elec tronegativity of the carbon is reduced and the metal-carbon bond will be more covalent with hydrocarbon group involved. Suppose a methyl group is attached to a metal, and this bond is exposed to water. A single water molecule has a distribution of charge, both H atoms are positive with res pect to the 0 atom. The H-0 dipole will be attacted to the M-C dipole and orientated in the appropriate direction! «®C-M « • £$H -O H $e The approach of the dipole continues with a corresponding loss in potential energy, until repulsion by the electronic shells equalizes the attraction. We now have a four-cen tered active intermediate which may break apart into the original components or realign its bonds to form new sub stances. If the change in free energy favours the latter, the products will bei C and M I I H OH Hydrolysis of a metallic alkyl therefore produces a hydro carbon and a metal hydroxide. The reaction is generally swift and violent for most metallic alkyls wIvto the m etal- 16 carbon bond is quite polar. When the metal-carbon bond is much less polar, as in (CH^^Si or (CH 3)2Hg, the reaction is extremely slow and must be accelerated by the increase of temperature and pressure or by the use of catalysts. Properties of Metallic Alkyls 1* General Trends in Physical Properties The properties of a metallic alkyl depend on both the nature of the cental atom and on the nature of the organic group(s) attached to that atom. Three trends of particular interest may be discussed using boiling points os a ty p ic a l physical property! a) Effect of the Organic Group(s)s The differences in the boiling points with different organic derivatives are explained quite sufficiently on the basis of sizes, shapes, and polarities of the organic groups! (C H ^S i b.p. 27° C CCH3)2Hg(CH3)2Hg b.p, 92° C (C2H5)lfSi 153 CH3HgC2H£ 127 (n-C^Ji+Si 212 (C2Hj)2Hg 159 (n-CVJ 9 )i£ i 275 (n-C3H7)2Hg 189 (n -C jH u ^ S i 318 This behaviour may be observed with the compounds of any element in Groups XXI through VII (excluding the transition elements in the a-subgroups) and the compounds of the Group lib elements zinc, cadmium, and mercury. The solid polar compounds of the more strongly electropositive elements of Groups X and IX are not volatile and cannot be compared in 17 this fashion. The substitution of branched-chain hydrocarbon groups for straight chain, or normal hydrocarbon groups generally increases the volatility of the metallic alkyli (n-C 5Hu )ifSi b.p. 318° C (n^Hs^Hg b.p. 8 V3 Ca ( 1-C5Hll^si 27? Ci-C3H8)2Hg 76 a a t 25 ran pressure b) Transitions Within a Given Groups With but few exceptions, the different elements in a given group all form the same general type of organic derivative. In any homo logous series, the weight and size of the parent element can be Important in determining differences in physical proper ties) except for the heavier periods of the Group lib metallic methyls, there is usually an Increase in boiling point with molecular weights Group ZIb Group II lb (CH3)2Zn b.p. 1+2° C (CH3) 3Ga b.p. 56° C (CH3 )2Cd 106 (CH3 )3In 136 (CH3) 2Hg 92 ( ch 3 )3t i 1W7 Group IVb Group Vb 0 O (GII^l+Ge b.p. u (CH3)3As b .p . 53° 0 (CH3 )i+Gn 78 Cch3 )3Sb 0 1 (CH3 )j+Pb 1 1 0 (ch 3) 3b i 110 c) Transitions Across a Periods The physical proper ties across a period are determined, not only by the polar ity of the metal-carbon bonds, but also by li.e molecular weight and symmetry of the compounds. In most cases, the 13 changes are gradual rather than abrupt. If the boiling point is considered a typical physical property, there is no set trend across a period: Group: lib I l l b IVb Vb VIb alkyl: (Cl^Cd (Cl^In (CH^Sn (CH^Sb (C.^Te b.p.: 106° C 136 78 81 82 2. General Trends in Chemical Properties A few broad generalizations can sim ilarly be made concerning the chemical behaviour of metallic alkyls under the following headings: a) Thermal Stability: In any one group, it is gener a lly observed th a t the compounds of the h eavier elements are less stable towards thermal decomposition than those of the lighter elements (except in Group lib). This trend is illustrated by the metallic alkyls of Group Illb: (CH^J^Ga k a lO1* ^ e- 59 , 500/HT (0 *3 ) 3^ k a lO1^? e-*+7,200/RI (0113)311 k = io 10*2 the. illfrilgJ&lg The chemistries of gallium, Indium, and thallium are closely related. With atomic numbers of 31» and 8l% respectively, gallium, Indium, and thallium have outer electronic configurations of the type ns 2np 1 where n has the values U, 5, and 6«respectively. Increases in atomic number and atomic weight are paralleled by increases in density, atomic volume, and atomic and ionic sizes* The metallic lattices have fairly weak bonding and are easily ruptured to yield low melting points. On the other hand, the boiling points are high with a slight decrease with increasing atomic weight. Thus the elements of this group are characterized by long liquid ranges, this property being most pronounced with gallium (rn.p. 30° C and b .p . 2070° C), 21 In this family the first Ionization potentials are low, as the removal of one electron requires less energy than for the neighbouring elements. There Is just one p electron In the nth quantum level, and since this electron Is less penetrating than the previously added s electrons, It Is better shielded form the positive nucleus by the electronic cloud around the element and thus easier to remove. However, the second and third ionization potentials are very high. Inasmuch as the outer electronic arrangements In the atoms of gallium, Indium, and thallium contain three more electrons than the pseudo inert gas structure ns 2np^nd*°, a uniform + 3 oxidation state is expected. This state Is characteristic of all of these elements but potential data indicate that tendencies to enter this state decrease from gallium to thallium. The + 3 state is largely covalent but tripositive ions are known in aqueous solution for all three of these elements. The ns 2np 1 electronic arrangement also suggests the + 1 oxidation state. This state is well known with thallium where oxidation potential data indicate that it is more stable in aqueous systems than the + 3 state. The stability of the + 1 state increases regularly with atomic weight in this family, the influence of the inert pair (the pair of s electrons in the nth quantum level) becoming increasingly more important for the heavier elements because of insuffi cient energy to cause unpairing. 22 Metallic Methvls of Group Illb R e lativ ely few organic compounds of gallium have been described, and those that have been were prepared from gal lium metal and the appropriate mercury alkyl or from gallium trichloride and the appropriate Grignard reagent. They are highly reactive, violently hydrolyzed by water (the lower alkyls being spontaeously Inflammable), but they are less reactive than their aluminum analogues. Trimethylgallium (m.p, -15° C) is a colourless liquid with a boiling point of 56° C. Trimethylgallium, unlike dimeric trimethylalumi- num, is monomeric in the vapour phase. The organic compounds of indium have not been studied extensively. Indium resembles gallium much more than thal lium in its organic derivatives and reactivity because of their similar electronegativities (both have values of 1. 6)* Trimethylindiura is a white volatile solid which melts at 89 , 5° C forming a colourless liquid which has a boiling point of 136° C, The vapour is monomeric* Trimethylindium can be readily transferred within a vacuum apparatus forming white needle-like crystals. The organic compounds of thallium are similar in their general chemical character to their gallium and indium ana logues, The trialkyls are prepared with the use of organo- llthlum compounds, since the action of the less reactive Grignard reagents proceeds only as far as the introduction of two organic groups to give the structure RgTlX. The failure of the reaction between thallium and organomercury 23 compounds, successful for the preparation of gallium and indium alkyls, is due to the low electronegativity of thal lium compared to mercury. Trimethylthallium is a white volatile solid that melts at 38.5° C forming a pale yellow liquid which has a boiling point of ?6° C a t 85 mm (lM-70 C extrapolated to 760 mm). Trimethylthallium should not be heated over 90° C for fear that it might detonate. The vapour is monomeric. Trimethylthallium can be transferred within a vacuum apparatus forming needle-like crystals. Trimethylthallium is stable if kept in the dark but darkens on exposure to light. Thallium has the only trimethyl in this group that reacts slowly with mercury at room tempera ture producing dimethylmercury and thallium amalgam. Mean Bond Energies by Calorlmetrlc Methods The calorlmetrlc methods for the determination of mean bond energies may be classified under two main classifica tions i solution calorimetry and bomb calorimetry (statlo and ro tatin g ). The data obtained in solution calorimetry allows the heat of reaction, which is usually a halogenation or a hydo- lysis, to be calculated. If the necessary auxiliary data are available, the heat of formation may then be calculated. The overall accuracy of the experimental results in solution calorimetry will depend upon the calorlmetrlc and chemical aspects of the investigation. However, the limiting factor in attainable accuracy is more the chemical rather than the 2k calorlmetrlc part of the determination Cv$J' The heat of formation of trimethylgallium has been obtained from the reaction of trimethylgallium with iodine in benzene solution at 55° C Z”13«7« With a molar ratio of trimethylgallium to iodine of 1»7, about 70$ of the iodine theoretically required for complete halogenation was used* With a ratio of It20 tho amount was 87 $. Of the total heat of reaction, about 80 $ was evolved in the first k minutes, and a fte r *+5 minutes the heat continued to be evolved at a rate of 0*3$ per minute* Because of the low solubility of iodine in benzene, higher concentrations could not be used) because of the low boiling point of benzene, higher tempera tures could not be used to Increase the solubility of the iodine. Because of these limits on the experimental con ditions used, 100$ reaction could not be acheived in a re- sonable time. From these experiments, AHf/"*(CH 3 )3Qa, liq_7 was - l 1*. $ £ 8 kcal/mole. The rather large limits of error are a result of errors in auxilllary data and the need to extrapolate to 100$ reaction* For metallic alkyls, the mean metal-carbon bond energy is obtained by the following equations 1 H(c) + nC(graphite) +, 3/2nH 2(g) — ► (CH3 )nM(g) M(g) — ► M(o) nCH3(g) + nH(g) ►nCHif(g) nCHlf(g) — nC(g) + 2nH2(g) l/2nH 2(g) ---- ► nH(g) nC(g) — »» nC(graphite) ______25 Adding, we obtain the result: M(g) + nCH3(g) ------► (CH3)^i(g) - AH where: • AH s Dx + D2 + ...... Dn s B Thus Dx + D 2 + ...... Dn equal %J + AH %J - nAH Z“CH3, %J In the case of trimethylgallium: AHf^ “(CH3 )3Ga, gJ s -6.7 1 8 kcal/mole AHf/~Ga, gJ « 65.6 £ 0 .5 kcal/mole AHfifCH3, %J * 32.6 1 1 kcal/mole Therefore Dx + D 2 +* D3 « 170.1 — 11.5 kcal/mole or B a 56-7 - **• kcal/mole. The data obtained in bomb calorimetry by direct exper imentation Is the heat of combustion from which may be determined the heat of formation of the compound studied. When the combustion of an organometallic compound takes place In a conventional statlc-bomb calorimeter, oxides of the metal and In certain cases the metal I ts e lf are formed in addition to the usual products from the organlo part of the molecule. The oxides are commonly found as a complex mixture and are often in such a finely divided state that their heat content differs from that of the bulk substances* In the combustion of trlmethylarslne the products are As, As203, As20if, and As 20j while in the combustion of trimethylgallium the products are Oa and Gap0 3 along with carbon dioxide and water. In combustion calorimetry, the actual process that UNIVERSITY OF WINDSOR LIBRARY % 5 n ? 26 occurs in the bomb must be related to the experimental heat of combustion. Thus we require the identity, the physical s ta te , and the amounts rf a l l products. Because of the ease of separation of the pijducts of combustion in the experi ments with either trimethylarsine or trimethylgallium, these requirements are met* The heat of combustion of trimethylarsine is given by the following equations (CH3)3As(1) + 602(g) ---- ► iAs203(c) + 3J02(g)+H H 20 (l) + 66^.6 t 1*2 kcal/mole Z"*9j7 The heat of formation of trimethylarsine can be obtained from the heat of combustion by the following equationss Ah(c) + ^02 ■ ■» iAs203(c) 3C(graphite) + 3^ — 3C02 (g) + 2i 02 — tyH20(l) jAsg Bond Dissociation Energies by the Kinetic Method The direct kinetic determination of bond dissociation ensrgles depends on the assumption that for the reaction + R]_ + R2 the activation energy of the reverse or reoomblnatlon reac tion is zero. Thus the activation of the forward reaction is equal to the energy of reaction, or the bond dlssodatlon energy. The assumption of zero activation energy for the recom bination reaction has considerable experimental 28 ju s tific a tio n In the case of atoms and small rad icals. An energy of activation would imply that two radicals of appro p riate spin approaching one another to form a molecule would suffer some repulsion before combining. Schematically this would be represented by a hump on the energy-inter atomic distance curve, or 'potential energy curve1, for the interaction of two radicals (Fig. 2, a). Much evidence on such p o ten tial energy curves where and R 2 are atoms has accumulated from band spectroscopic studies, and the re su lts show that usually no such potential maximum as shown in Fig. 2 , b occurs. The rotating sector method has been applied to the determination of the rate constant of methyl radical recom bination in the photo-decompositions of acetone (at 125° C and 175° C) and dlmethylmeroury (a t 175° C and 220° C), using the small but accurately known rate of methane foxma- tlon as a measure of the methyl radical steady-state concen tration /*2lJ7. The resulting value of the reoomblnatlon rate constant is if. 5 X lO1^ cc/mole-seo, with an activation energy of E s 0 t 700 cal/taole regardless of the radloal source. A second determination of the rate constant of methyl radical recombination using the photo-decomposition of acetone (at 135° C and 165° C) by the rotating sector technique f22J gives a value in agreement with the above work. If there is no potential energy barrier for the recom bination of two radicals, the transition state theory 29 t 8 a. DISTANCE OF SEPARATION OF THE TWO RADICAL FRAGMENTS Fig. 2s Potential energy curve for a unimolecular decom position into two radicals. Curve 4 represents a finite energy of activation for recombination. Curve b represents a zero energy of activation for recombination. 30 predicts that for a unlmolecular reaction the rate constant is given byi k - K k'T 0»(T) e“D/RT h 0(T) The total partition functions, 0(T) for the normal molecule and 0'(T) for the activated complex, may each be separated into translational Z."”A(T)«.7, rotational jfr(T)/o[7, and vibrational ^“v(T)J7 contributions. The translational partition function ACT) « <2 Tmk,T)3/ 2/h 3 will he the same for the normal molecule and the activated complex. The rotational partition function will be r(T)/ k = K k*T 6' rA«B«cO* 3 TT(1 - e"hv/k If hv^^k’T, then (1 - e"hv/^*T) « hv/k*T, and we obtaini 31 k - K £' fA'B'cO* 3t 7T(v) e“D/BT cf» LABG J 3n-7 7TU») Taking logarithms of both sides of this equation and differ entiating with respect to temperature givesi d(ln k) - D. " i r s p The Arrhenius activation energy is therefore equal to the bond dissociation energy. At the other extreme, if hv»k'T, (1 - 0-hv/kfTj & such th ati k a K iLlX a-0/* 1 € L ABC J h Taking logarithms of both sides of this equation and differ entiating with respect to temperature givesi d(ln k) « D ..+ BT dT RT* Therefore the limits D E D ♦ RT may be placed upon the experimental activation energy. Thus if the experimental activation energy for a unlmolecular decomposition can be accurately determined, it should be a reasonable approxi mation to the bond dissociation energy. Pressure Dependence of Bond Dissociation Energies One of the most satisfactory and realistic theories of unlmolecular reactions is that of Slater Z~23j7« For his model, S later takes a polyatomic molecule in which a l l os cillators are classical and harmonic. The molecular motions are described in terms of a series of internal coordinates, 32 and reaction is supposed to take place when a specified coordinate attains a critical value. If the reaction under consideration is the dissociation of a molecule into two radicals| the critical value of the specified coordinate is the critical length between the two atomic nuclei being separated in an activated molecule. If enough modes of vibration come into phase in the same instant, all of them together can achieve the critical value in the specified coordinate and lead to the rupture of the bond. The ob served first order rate constant is the rate of decomposi tion of this activated molecule into products. Slater defines the activation energy Bj° at high con centration to bet I? s H ddn k) d l keeping either concentration or pressure constant, and this reduces to E0 in the Arrhenius case where the activation energy was defined as the critical (minimum) energy for dissociation. Slater has also postulated that if the unlmolecular rate constant is measured in the pressure dependent region, the experimental activation energy E is related to the ex perimental activation energy at infinite pressure B 0 (Bj°) by the relations E • E0 - * n* RT g(0) where n' is equal to the number of effective oscillators in the molecule and g(0) represents the fractional drop of E 33 from the high value (E0) to the low value (E 0 - £ n1 RT). The function g(0) is related to the amplitude factor in the c r itic a l coordinate and goes from zero to unity. In the previous section it was shown that the experi mental activation energy E for a unlmolecular dissociation lies within the limits D £> E D 4* RT. The assumption that R • E0 was Inherent in the derivation of this result. Therefore, if the experimental activation energy has been determined in the pressure dependent region, the magnitude of E0 - E must be determined to estimate the bond dissocia tion energy. The calculation of kAoo and henc® of g(9) requires a complete vibrational analysis of the molecule In question* This is generally not available. The approximate value of kAoo nay be obtained from the slope of log k versus log P obtained experimentally. Values of kAoo as a function of the pressure dependent parameter 0 have been tabulated by Slater for values of n' from 1 to 13* Because no complete vibrational analysis Is available for the molecule in question, it is necessary to arbitrarily choose a value of n*, the number of effective oscillators in the molecule. For a non-linear molecule, there are 3n - 6 vibrational degrees of freedom ( 3n - 5 if linear). However, in a molecule with several heavy nuclei the con trib u tio n s from the C-H bonds w ill usually be small except for the contributions from those bonds near the point of rupture. For purposes of further calculations, the number 3W of effective oscillators will be taken as -}-( 3n - 6 ). For dimethyl metals, n' may reasonably be assigned a value of about 10. The value of kAoo obtained from the experimental data for these these Compounds at 13 mm is 0.*f0. This corresponds to a value for g(0) approximately equal to 0.35 Hence at 700° Kt B E0 - 2.5 kcal/mole The effective number of oscillators in trimethyl metals may reasonably be assigned a value of 16. The value of kAoo obtained from experimental data for these compounds at 13 mm is approximately 0.95 and th is corresponds to g(Q) approxi mately equal to 0 . 0U-. Hence a t 700° Kt B B0 - 0«*f kcal/mole For methyl metals, n' may be asigned a value of 8 . Slnoe kAoo *8 about 0.*K>, g(9) is 0.35. Hence at 700° Kt B B0 - 2.0 kcal/mole For the compounds studied, i t is not unreasonable to assume hvA 'T 1 a t 700° K (vs* 1013). Hencet E0 £0 D +> 0.82T = D + 0.7 kcal/mole Therefore the errors obtained in assuming D z E w ill be 0*3 to 1 .8 kcal/mole. In the following sections, the following corrections will be made to the experimental activation energiest I>1 T Ei + o kcal/toole D2 - E2 + 1.8 kcal/mole D3 2 E3 + 1.3 kcal/mole 35 The Toluene Carrier Gas Technique The problem of determining bond dissociation energies by the kinetic method is reduced to that of finding the activation energy of the unlmolecular dissociation processt R3R2 ► Ri + R2 The Investigation of the kinetics of the process may be complicated by various secondary reactions such as the re combination of Ri and R 2 or abstraction from R 1R2 by eith er Rl or R2« The first reaction leads to a loss of product, while the second might in itia te a chain process. Consequen tly the k in etics of the whole process can be very complex and difficult to Interpet. A useful method which in some cases insures th at com plicating side reactions do not confuse the kinetics of the unlmolecular dissociation reactions is the toluene carrier technique ^2*+, 25„_7. Toluene reacts readily with various radicals or atoms according to the equations R + C6H5-CH3 -----► C6H5-CH2 + RH The radicals react preferentially with the toluene which is present in a very large excess, each radical being therefore completely surrounded by toluene. The formation of the stable molecule RH prevents the back reaction and possible side reactions. The benzyl radicals do not react in the hot zone under the experimental conditions used, and eventually dimerize outside the reaction zone. To prevent the forma tion and decomposition of dibenzyl in the reaction zone, short contact times (approximately 1 to 2 seconds) and high 36 flow rates (flow rate of toluene should be at least 100 times greater than the flow rate of the compound to be decomposed) are used. The rate of in itia l dissociation may be measured by the formation of products of the type RH, C6H5-CH2-R, or by the measurement of dlbenzyl its e lf . Under 700° C, the decomposition of toluene is negli gible, being less than 0. 0l£ /~26_7, and approaches 1% decomposition at 800° C. The thermal decomposition may be represented by the following mechanlsmi C6H5-CH3 ------C6H5-CH2 H + C6H5-CH3 -----» C5H5-CH2 + H2 and H + C$H5-CH3 ---- » C$H£ ♦CH3 CH3 C6H5-CH3 ---- ► C6H5-CH2 + CHI4. followed by the dimerization of the benzyl radicals. The quantity of dlbenzyl recovered is one mole of dibenzyl per mole of gas (H 2 and CHi* in the ra tio 60s*f0) produced. More recent investigations indicate H 2 and CHit are produced in the ratio of 67*33 7 and the f i r s t order rate constant for the thermal decomposition of toluene is given by* loglO k (sec"1) * 1^.8 - (85, 000/ 2. 303RT) It is important to make clear the limitations of the toluene c a rrie r technique. This method cannot be used for the determination of bond dissociation energies greater than that for the carbon-hydogen bond in toluene unless a dif ferent product is formed. Even if such a product is formed, the large quantities of H 2 and CHi* produced often create physical problems unless they can be continuously pumped away without losing the desired product. The most favour able case is th at in which the dissociation energy of the bond to be broken is at least 10 kcal/mole lower than D/f - c 6H5CH2- H 7 . Secondly, the radical or atom produced in the initial dissociation should react easily with toluene to produce the stable molecule RH. It is also possible to use this tech nique even if the in i tia l radical decomposes producing a new radical that reacts with toluene. On the other hand, it might appear that the toluene carrier technique could be used to determine the dissociation energies of very weak bonds. This is not the case. For a very low bond dissocia tion energy, the temperature required might be so low that the abstraction reaction would be too slow to remove the radical R, since this reaction requires some activation energy /"*28 J, However, even at these low temperatures where the methyl radicals released dimerize to a large ex tent, the toluene still performs its essential function of reducing any attack of the released radicals on the parent substance. Kinetics of Unlmolecular Decompositions In the unlmolecular thermal decomposition of a metallic alkyl, the activated complex consists of a single activated reactant molecule which follows first order kinetics. The mechanism of decomposition may be represented by: Let the Initial concentration of A be a moles per cc. At any time t: - d EA1 s ki CAl Separating the variables and integrating, we obtaim In £A3 = -kxt a or CAl s a e“^l* The most common form of this equation and the one that will be used in this work is: kl ■ 2.303 iog a - t c a - x where x is the amount of A th at has decomposed. If we have a series of consecutive reactlonsi A B + Rx B -12%. C + R2 the total concentration remains constant: a = CAl + CBl + CC3 The net rate of formation of B is the rate of its formation from A minus the decomposition of B to give Ci d CB3 = kxCAl - k 2[B] d t = kx a e”kl t - k 2 CBl Integrating, we obtain: [B] = a kX (e*kl* - e-k2t) k2-k i The concentration of C is obtained by: [C] = a - (fA] 4-Cb3 ) 39 In the step-wise decomposition of a metallic trimethyl, we have: m(ch 3)3 m(ch 3)2 + ch 3 m(ch 3 )2 -IS*. m{ch3 ) + ch3 The total methyl radicals released equals M(CH 3>2 + 2 MCCH3 ) total methyl radicals = [B] 4 * 2033 Substituting for CB] and Cc] from above, we obtain the consecutive order equation: methyl a a [2 + kl (e"klt + 6^ 2*) - 2 k2 e"kl * | ra d ic a ls L * 2-* ! k 2”kl -J Kinetics of Methvl Extraction In the thermal decomposition of metallic methyls, methyl radicals are released into the toluene carrier flow system, and their reaction with toluene, i.e. the abstrac tion reaction, is given by: ch3 + C6H5-ch3 — ► C£H5-ch2 + chi*. The rate of formation of methane is given by: dtCHl+1 = ka [cH3] [C6H5-CH3] d t Methyl radicals are also removed from the system by the com bination of two methyl radicals: CH3 + CH3 -----► CH3-CH3 The rate of formation of ethane is given by: d CC2H6] - k r [CH3] 2 d t From the rates of formation of methane and ethane, we obtain the following equation: kr* (d[C2H6]/d t) ^ LC6H5-CH3I The rate of formation of methane or ethane during a run is found by: dfcHit or C2H6] a total CHU. or CpH6 obtained dt reaction volume X time The result is in moles/cc/sec. The concentration of toluene in moles/cc is obtained by: tc6H5-°H3l: g s The most usable form of ka/kr^ is given by: ka - ( to ta l methane) x 1 x 62360T kr* (total ethane)* (rx vol X time)® p which has the units (cc/mole-sec)^. The value of kr has been obtained from rotating sector experiments /~21, 22_7, and consequently a value for ka can be calculated from experimental results. However it is more convenient to assume that the methyl radical combination reaction has zero activation energy. The normal form of the Arrhenius equation is given by: k -- Ae-E' m Alternately, we may write: log k = log A - E/2.303RT Differentiating with respect to T, we obtain: d £&. ■ A° e ' E a / R T kr* Ar» e-iEr/M Rewritting: d(log kaAr^) _ Ea “ ^Er Ba d(l/T ) ” * 2.303R * 2.303R since the methyl radical combination reaction has zero activation energy. Thus, from the Arrhenius plot of ka/kr^> the activation energy for the abstraction reaction is given by: Ea = - 2.303R X slope CHAPTER I I I EXPERIMENTAL Preparation of Materials 1. Toluene a) Toluene was prepared by the diazotization of o-tol- uidine followed by deamination with sodium hypophosphite. The organic layer was dried over anhydrous calcium chloride and then fractionally distilled using a 1-meter glass bead packed column. The fraction boiling 109 - 110° C (uncor rected) was dried by refluxlng over sodium ribbon under vacuum and then degassed by bulb-to-bulb d i s t il l a t i o n . Toluene prepared in this manner was found to be more suitable than the sulphur free reagent grade toluene pre viously used which required 30 % prepyrolysis in order to ob tain reproducible rate constants in the pyrolysis of toluene itself Z”27j7. b) Toluene from sulphonic acid (Eastman Organic num ber X 325) has been found to be as suitable as that des cribed above. It was dried by refluxing over sodium under vacuum and then degassed by bulb-to-bulb distillation. 2. Trimethvlfralllum Trimethylgallium was prepared by refluxing pure gallium metal with dimethylmercury in an atmosphere of dry nitrogen k2 ^ 3 Z~29_ /• The o v erall re actio n is given by: 3 Hg(CH3 )2 + 2 Ga ----- ► 2 Ga(CH3)3 + 3 Hg A trace of mercuric chloride was added as catalyst with the formation of methyl mercuric chloride as the intermediate. The reactants and the catalyst were initially placed in a quickfit flask equipped with a take-off head. After 2*+ hrs the temperature in the take-off head dropped from 92° C (b .p . of dimethylmercury) to become steady a t 56° C (b .p . of trimethylgallium. Small fractions were taken at $6° C over the next 2V hrs until only a residue of about 1 cc was left in the flask. The conversion was virtually complete and no purifica tion of the product was necessary. The fraction boiling at 53*6° C at 71^ mm was frozen down with liquid air and trans ferred to a degassing system. The sample was degassed by uuJLb~ Co-bulb distillation in vacuum and stored under its own vapour pressure a t -190° C. The m elting point was found to be -16.5° C and the vapour pressure was 65 mm at 0° C, both values in agreement with literature values 3. Trimethvlindlum Trimethylindium was prepared by refluxing pure indium metal with dimethylmercury in an atmosphere of dry nitrogen Z~3o J 7» The overall reaction is given by: 3 Hg(CH3)2 -f 2 In -----* 2 In(CH3)3 + 3 Hg A trace of mercuric chloride was added as catalyst with the formation of methyl mercuric chloride as the intermediate. ¥ f After 8 days, the reaction flask was cooled to 0° C (vapour pressure of trimethylindium: 0.2 ram) and the unreacted dimethylmercury (vapour pressu re: 17 mm) was d is tille d o ff. The crude trimethylindium was then distilled into a degas sing system and purified by repeated degassings at 0° C. The final product had a melting point of 89.5° c and a vapour pressure of 37 mm a t 60° C, both values consistent w ith lite r a tu r e values Z”30_7. The trim ethylindium was stored under its own vapour pressure at - 190 ° C. 1+. Trimethvlthallium Trimethylthalliura was prepared by adding dropwise an ether solution of methyllithium to a suspension of dry powdered thallous iodide in anhydrous ether containing methyl iodide /,~31> 32,_7. The m ethyllithium was prepared by adding methyl iodide dropwise to a suspension of finely cut lithium metal in ether £"33_7* Tlie thallous iodide sus pension was stirred at room temperature under a dry nitrogen atmosphere. As each drop of methyllithium hit the suspen sion, a black dot (finely divided, highly reactive thallium) formed momentarily and then disappeared. As the addition of methyllithium progressed, the suspension became darker. After standing for 36 hours the mixture cleared. The over all reaction is given by: 2 CH3M + CH3I + T i l ------► 11(0113)3 + 2 HI The reaction mixture was heated in a water bath at 75° C to distill the ether. Maintaining the water bath a t **5 this temperature, the residue was then vacuum distilled into a trap at -30° C. The crude metallic alkyl was tranferred to a degassing system where the remaining ether was removed by repeated bulb-to-bulb distillations with the cold trap at 0° C. The final product had a melting point of 38.5° C and was consistent with the literature value Z~32_7. Trimethyl- thalliura in the pure form was always handled and stored in the dark as it was sensitive to light. Vapour pressures were measured from -25° C (1.0 mm) to 60° C (17.5 mm). The vapour pressure data of Gilman and Jones j T ' & . J from 5*+° C to 7^° C gave vapour pressures that were higher than those obtained here (*+5 mm at 60° C compared to 17.5 mm), and this was probably due to decomposition at higher temperatures and exposure to light. ApparaAuq The toluene carrier flow system used in this work is shown in Fig. 3. The description of this system may be discussed under the following sections* 1. Vacuum System The source of high vacuum was a two-stage mercury dif fusion pump (Precision Glass Company, Toronto, Ontario) backed by a two-stage oil-sealed Rotary Vane Pump DUO 5 (Balzers, Principality of Liechtenstein). To prevent oil or mercury from entering the system, a liquid air trap was interposed before the main body of the system. All ground glass joints and heated taps in the system were lubricated E 0)E *M P O w H to tn ^ u £ h o o Cli rH •H pt, 'O(0 ■HO#o cfl • P fn r t ^ o I CU> , E ® £ I »H O*H J - •* I 0) . >»P I x : X C • * o H O « I t o o ctf \ 7 regularly with High Vacuum Silicone Stopcock Grease (Dow Corning Corporation, Midland, Mlchagan). Unheated taps were lubricated with Apiezon N Grease (Associated Electrical Industries, London, England). The degree of vacuum in th e system was read on a McLeod Gauge constructed to measure pressures as low as 10"^ mm of _If mercury. A vacuum of 10 mm or better was considered to be a workable vacuum. 2. Carrier Gas Storage and Control The carrier gas used throughout this work was toluene, purified as previously described, and stored in a vessel (R^) of about 150 cc. The vessel was attached to the main system by means of a #l*f ground g lass standard tap er Jo in t so that it could be weighed before and after each run. Car rier control was maintained by a constant temperature bath. Cooling effects due to vaporization were counteracted by use of an immersion heater in the bath. The toluene pressure (the pressure in the reaction zone) was read on a di-octyl phthalate-mercury differential manometer (Mi). The sensing side of the manometer consisted of 25 mm OD tubing; the responding side consisted of l*t mm OD tubing with 2.1 mm ID capillary. This combination gave a monometer so constructed that a 1 mm pressure on the sensing side gave a 9.06 mm rise in the capillary. 3. Metallic Alkyl Storage and Control Each metallic alkyl was introduced into the system by If8 degassing under vacuum in to R2 *. About 3 grams were dis tilled into a small vessel (R2) attached to the system by a #l!+ joint so that it could be weighed before and after each run. The in je c tio n system shown in F ig. was used fo r trlm ethylgallium and th a t shown in F ig . 5 was used f o r t r i methylindium and trimethyl thallium. a) Construction: The furnace consisted of a quartz cylinder, 3 inches in diameter and 2*t inches long, wound on the outside with Chromel-A Resistance Ribbon (Hoskins Manu facturing Company, Detroit, Michigan). The ribbon was about 2 mm wide and about 0.2 mm thick, giving a resistance of 0.603 ohms per foot. The windings were cemented into place by Sauerelsen Cement, Number 31 (E.H. Sargent and Company, Detroit, Michigan). To obtain an even temperature profile in the centre 8 Inches of the furnace, the windings were arranged as shown in F ig . 6. The to ta l re sista n c e of th e furnace was 60 ohms. The heating elements were tapped at 7 points so that the heating could be adjusted by shunt resistances. An lnconel liner, 2.5 Inches in diameter, 12 inches long, and 0.25 Inches thick, was placed in the centre of the furnace to smoothen the temperature profile in the centre of the fur nace and give a sharp temperature fall-off at each end. A typical temperature profile is shown in Fig. 7* The wound quartz tube was centered in a box (2*+w X 12" **9 to furnace from toluene reservoir □ to mercury alkyl manometer storage F ig. ht Injection system for a volatile metal alkyl, as used in the experiments with trimethylgallium. 50 to from furnace toluene re se rv o ir alkyl storage F ig. 5i Pick-up system for metal alkyls of low volatility, as used in the experiments with trimethylindium and tri- methylthallium. 51 cen tre lin e of furnace d istan ce from a cen tre "I lin e in inches tu rn s per inch tap tap tap tap Fig. 6: Placement of heating windings in furnace construc tio n . thermocouple o placement % o U4> 3a? platinum a>U re sista n c e P« thermometer E 01 placement ¥ 6 H 16 10 Distance from exit end (inches) Fig. 7i A typical temperature profile. UNIVERSITY OF WINDSOR LIBRARY 52 X 12") with a frame of three-quarter inch angle iron and sides of asbestos board one-quarter inch thick. Similar ends, but with 3**inch holes to accomodate the quartz tube, were fitted. All seams were filled with asbestos cement (E.H. Sargent and Company, D e tro it, M ichigan). The box was filled with powdered alumina C-l (particle size 50 mesh, low density - approximately 1.8 grams per cc, gift of the Alumi num Company of Canada, Toronto, Ontario) for insulation. The maximum operating temperature was 1000° C. b) Temperature Control! The centre 8 inches of the furnace, the area where the reaction zone of the reaction vessel was situated, was constant in temperature to within t 1° C. Accurate and reproducible temperature control was achieved by the use of a Sunvlc Platinum Resistance Thermo meter Controller, Type RT2 (Sunvlc Controls Limited, London, England). The temperature was read in the axial thermocouple well of the reaction vessel using a Chromel-P-Alurael thermocouple (28 gauge w ire, Hoskins M anufacturing Company, D e tro it, Michigan) in conjunction with a m illivolt potentiometer (model 8691» Leeds and Northrup, Philadelphia, Pennsylvania). 5. Reaction Vessels A reaction vessel consisted of a quartz tube, bo mm OD and 8 inches long, sealed to 20 mm OD ends. An axial ther mocouple well constructed of 10 mm OD tubing ran the length of the reaction vessel. Graded quartz-to-pyrex seals were 53 situated a few centimeters beyond each end of the furnace. The average re a c tio n volume was 195 cc. For temperatures below *+60° C, similar vessels were constructed of pyrex. To test for surface effects, a quartz vessel was packed with fine quartz tubing, 3 mm OD and a wall thickness of 0.8 mm, increasing the surface-to-volume ratio by a factor of 12 and reducing the volume to 1 cc. The packing com pletely filled the cross-section of the rerction zone. The flow through the re a c tio n zone was regulated by a control capillary (CC, Fig. 3)» 1 mm ID and *t0 mm long, sealed in at the outlet of the reaction vessel. 6. Product Separation. Collection, and Analysis Beyond th e co n tro l c a p illa ry a t the o u tle t of the reac- tlon vessel, a high capacity trap (Tx) maintained at -80° C with an acetone-dry-ice sludge removed unreacted alkyl, tol uene, ethylbenzene, dibenzyl, and similar products. A mer cury diffusion pump transferred the remaining products to a second trap (T2) maintained at -100° C with an acetone-tol uene sludge to remove hydrocarbons higher than Ci+'s. The remaining gaseous mixture was tranferred past a non-return valve to a gas burette (calibrated volumes: 0.M+, *+.3*+> ^5.36, and 1^2.9 cc) with the aid of a Toepler Pump. A small McLeod Gauge (M^) indicated complete transfer of the products to the gas burette. After each run, a sample was taken for chromatographic * analysis. A portion of this sample was accurately measured in a gas burette adjacent to a gas chromatograph (Model 15*+, Perkin-Elmer Corporation, Norwalk, Connecticut). Using a 2- m etre s ilic a gel column (Perkin-Elmer Column J) a t 80 C, with a helium flow rate of approximately 20 cc per minute, internal standards were run with each set of analyses so that peak heights could be used. The contents of were analyzed using a temperature of 7 5 ° C in a Model 800 Ges Chromatograph (Perkin-Elmer Corporation, Norwalk, Connecti cut), equipped with a 150 foot Golay Column (Perkin-Elmer Column R), 0.02 inches ID coated w ith polyCpropylene g ly co l). Hydrogen was analyzed by allowing an. original sample from the gas burette to be in contact with tiny pellets of copper oxide for 15 minutes in a furnace maintained at 275° c. > Experimental Technique After the furnace reached the desired temperature and the vacuum was 10~** mm or better, a run could be carried out in the following manner. The weighed toluene storage vessel R^ (Fig. 3) con tained degassed ready-to-use toluene. A fixed temperature bath was placed around the vessel to obtain the desired pressure (examples a bath of 1*+° C gave an operating pres sure of 13 min). The weighed metallic alkyl storage vessel R 2 contained degassed ready-to-use alkyl. In the study of trimethyl- 55 gallium, a small sample ( 0.2 to 0.3 grams) was distilled from R2 into the alkyl finger (Fig. M-). A fixed temper ature bath was placed around the finger to obtain the de sired pressure (examples -20° C gave a pressure of 20 mm). The alkyl pressure was such that at all times the minimum acceptable pressure difference was 5 mm to insure against pressure surges that might cause toluene to enter the alkyl injection system. This pressure difference also determined the concentration of the alkyl passing to the reaction zone; higher pressure differences gave larger concentrations of alkyl and decreased the toluene-to-alkyl ratio. To start a run, the flow of toluene was commenced and the pressure mea sured by the differential manometer. After a 3 t o 5 m inute flow of toluene to stabilize flow conditions, the trimethyl- gallium vapour was injected into the toluene stream through a fine capillary sealed to the base of a stopcock Sx (Fig. *f) at the top of the alkyl reservoir. The flow of alkyl con tinued from 20 to 120 minutes (depending on the reaction conditions) and was followed by another 3 to 5 minute flow of toluene alone to remove all products from the reaction zone while conditions were still stabilized. The alkyl re maining in Fx was redistilled into fig. The amounts of tri- methylgallium and toluene used were determined from the weight losses of R2 and Rx respectively. In the studies of trimethylindium and trimethylthallium, approximately 0.1 t o 0.2 grams of alkyl were distilled from R2 into the U-tube projection P (Fig. *>)• The entire sample 56 In the U-tube was used in the run. After a 3 to 5 minute flow of toluene by-passing the U-tube, stopcocks S 3 and were opened to allow the toluene to sweep the alkyl vapour to the reaction vessel. The alkyl concentration and the toluene-to-alkyl ratio were controlled by the proper manipu- lation of stopcocks S 3 , Sif, and S 5 in conjunction with the temperature of the projection. The alkyl run was ended when the last crystal of alkyl was observed to sublime into the toluene stream. A 3 to 5 minute flow of toluene alone re moved a ll products from the reaction zone whileconditions were still stabilized. The amounts of trimethylindium or trimethylthallium and toluene used in a run were determined from the weight losses of R 2 and Ri,respectively. In the runs with trimethylthallium, the entire system was kept in the dark to neutralize the light sensitivity of the compound. All tubing on the inlet side of the reaction vessel was maintained at about *f0° C to prevent condensation of either the carrier or the alkyl. The injection system was heated as required. The tubing from the outlet of the reaction vessel to trap T^ was heated to about 60° C. Trap Ti cooled to -80° C with an acetone-dry-ice sludge removed unreacted alkyl, toluene, ethylbenzene, dibenzyl, and similar products. The remaining products were trans ferred by a diffusion pump to a trap cooled to -100° C with an acetone-toluene sludge to remove traces of toluene and hydrocarbons higher than Clf's. The remaining gaseous mix ture was then transferred past a non-return valve to a gas 57 burette with the aid of a Toepler Pump. After the gaseous mixture was measured, a sample was taken for chromatographic a n a ly s is . In several of the runs, the contents of the acetone- dry- ice trap were analyzed for the metal content. After adding 50 ml of concentrated hydrochloric acid, the mixture was twice evaporated to near dryness. The solution was dil uted with distilled water to a volume of 50 ml• Analysis for gallium was carried out by titration with 0,01 M potas sium ferrocyanide using 3,3*-dimethyl naphthadine in the presence of a trace of potassium ferricyanide (freshly pre pared) as indicator Analysis for indium or thallium was carried out by buffering the weekly acidic solution with hexamethylene tetramine and titratin g with 0.02 M EDTA using xylenol orange as indicator Z“35«7» In several of the runs, the contents of the reaction zone were sim ilarly analyzed for its metallic content. The first order rate constants were calculated from the equations k - 2.303 log 1 (sec"*) t c 1 - f wheres f s fraction of the metallic alkyl decomposed te ■ contact time, and is given bys t„ - (rx volume )(FWi)( 273) sec wheres Vf ■ rate of flow of gns through the reaction zone (moles/sec). CHAPTER IV EXPERIMENTAL RESULTS The Pvrolvsis of Trimethylgalilum The pyrolysis of trimethylgalliura has been carried out in the toluene carrier flow system from 686° K to 983 ° K using total pressures from 6.1 mm to 31.1 mm. The progress of the reaction was followed by measuring the amounts of methane, ethane, and ethylene formed. The complete experimental results are given in Tables 1, 2, and 3* Analysis of the data indicates that the ther mal decomposition of trimethylgalilum does not occur by the simple release of three methyl radicals. It was found that even at 1075° K no more than two-thirds of the theoretical quantity of methyl radicals could be accounted for. This was sim ilar to the decompositicn o f trimethylantimony where the formation of (SbCH^)n was indicated. To test for the formation of a similar gallium polymer, a black deposit scraped from the reaction zone was analyzed. The results of this analysis indicated: 80# gallium (I) oxide, 8£ raethyl- gallium polymer, and 12# carbon. The carbon is probably due to decomposition of the carrier in the high temperature runs. 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C Mle v C M C O O O O O O O O O O O O 000 - - -vO '-O ^-C C O Vv«H O O O O O COtHlTVrH COtHlTVrH Jsr r J r rr IrsrH Vr UvCMOO UvCMOO O O O r o _ + O ' ' O + _ o r oxrvlrv C^vO C^vO lvO O lev CM O O O CM O O XT v •H ■p © o o cd p c cn 01 rH © © 0 o cn E 1 61 62 reaction of oxygen with the methylgallium polymer. Sub sequently, analyses were carried out on the contents of the acetone-dry-ice trap and on the deposit in the furnace fol lowing each of a series of experiments. Under conditions such that less than one-third of the theoretical yield of methyl radicals was observed, the gallium was found to be quantitatively in the acetone-dry-ice trap. At temperatures above which two-thirds decomposition occurred, the gallium was found quantitatively in the reaction vessel, as a thin, apparently non-metallic film. It therefore seems plausible that methylgallium does not decompose, but deposits in the reaction vessel as (GaCH3)n. The following mechanism was proposed: Ga(CH3)3 - ch3 ( 1) Ga(CH3 )2 ------► Ga(CH3) + ch3 (2) n Ga(CH3 ) ----- ► (GaCH3)n (3) + C£H5-ch 3 - CHl*. (a) 2 CH3 ------► CH3-CH3 (r) 2 C6H5-CH2 -— ► (c 6h5-ch 2)2 (>0 The ethylene and the hydrogen observed in small amounts re sult from the reactions: CH3 + C2H6 — *■ Cj>Hij ♦ CHi* (?) C2h? — ► C2Hif + H (6) H + C6H5-CH3 — * C6H5-CH2 * H2 (7) In the runs with low toluene-t©-alkyl ratios, propane, ethyl- benzene, end xylenes observed in small amounts result from the reactions: 63 CH3 + C2H^ -----». G2H5-CH3 (8) C6K5-CH2 + CH3 ------C6H5-CH2-CH3 ( 9 ) CH3-C6HI* + CH3 ► CH3-C6HI4.-CH3 (10) Reaction (10) occurred to a very small extent because reac tion (a) proceeded mainly as written but with a small per centage of abstraction from the ring. The values of ^aAr^ given in Tables 1, 2, and 3 have been calculated using the equation: ka _ [moles CHiJ x 1 x 1 [moles C2H6 C2Hlf]^ t$ [toluene] If in the decomposition of a compound of the type M(CH3)n we have: M(CH3)n ------» M(CH3)n. y + y CH3 (11) occurring over a temperature range T^ to T2 while: M(CH3)n. y ------* M(CH3)n„y.z + z CH3 (12) occurs appreciably only above T2* we w ill have a number of factors which will influence the value of ^aAr^* First, in a flow reaction, the temperature increases as the reaction zone is approached; therefore when the temperature in the reaction zone (T3) is above T2, reaction (11) will occur partly in the tube leading to the reaction zone and will be complete in some small fraction of the zone. This has a dual effect on kaA r^* i) reaction (11) is occurring at an average temperature above T2 but below T3, li) the volume over which reaction (11) occurs is no longer the total volume of the reaction zone. 6 b The net effect is to hold the apparent observed value of ^aAr^ approximately constant as the temperature in creases. Actually, the net effect might be a slight de crease except for the fact that reaction (12) is occurring over the entire reaction zone at T3» Experimentally, for dimethylzincs Zn(CH3)2 ---- ► Zn(CH3) + CH3 (13) Zn(CH3) --► Zn ♦ CH3 (1»+) the ratio shows a slight decrease above T2 The Arrhenius plot of ka/kr^ f or the present work is shown in F ig. 8 . In th is case th e c h a ra c te ris tic break in the curve occurred at 33 % theoretical yield of methyl rad icals and the ratio continued to rise only slightly. Thus it was apparent from the analysis of the data that the se cond methyl radical was not immediately released after the f i r s t . According to the mechanism, the number of moles of methane plus twice the number of moles of ethane and ethy lene formed during a run (correction being made for any car rier decomposition at higher temperatures) should be equal to the total moles of methyl radicals released. Below 820° K the methyl radicals released were essen tially due to the first bond rupture. Thus the fraction of trimethyl- galiium decomposed was given by* moles of methvl radicals released # moles or alkyl used Above 8*+0° K, the methyl radicals released were essentially due to the successive ruptures of the first two bonds. Thus 65 1 I J , 04 ■ 6 o « t \ G a ( C H ^ 2 O' 0 0 \ \ \ e Q ® ® e ^ V tooo/r Fig. 8: Arrhenius plots of rate constants for the decom position of trimethylgallium and dimethylgallium and the reaction of methyl radicals with toluene. 0 rate constant; 9 ^a/kr£. Subscripts denote the number of runs averaged to obtain the given point. 66 the fraction of dimethylgallium decomposed was given by* moles of methvl radicals released - moles of alkyl used moles of alkyl used Between 820° K and 8M-00 K, the methyl radicals from the thermal decomposition of dimethylgallium became appreciable. The rate constant for the thermal decomposition of tri methylgallium was thus calculated frcw the usual equation fo r consecutive unimolecular reactions by the method of successive approximations* Ills.] - ba,J] [» * & , - ! -H The value of k 2 used in the above equation was obtained frcm the Arrhenius plot for the decomposition of dimethylgallium (Fig. 8) extrapolated to the temperature range between 820° K and 8*t0° K. Since any methyl radicals due to the decomposition of dimethylgallium tended to raise the value of ki, lower values vf k]_ were used in the above equation. Only one or two approximations were required to obtain sub stantial agreement between (methyl radicals released)caic. and (methyl radicals released)0p8» The percentage decom position of dimethylgallium was of the order of at 820° K and 7% a t 8»+0o K. The mechanism further assumed that the methyl radicals were not removed by any reactions other than the abstraction and recombination reactions. Extensive work with dimethyl* mercury by Gowenlock, Polanyi, and Warhurst /~36J7 has shown 6 7 that the percentage decomposition based on total methyl rad icals released in the form of methane, ethane, and ethylene was in good agreement with that calculated from the weight of mercury produced. The loss of methyl radicals by reac tions (8), (9), and (10) was therefore negligible under or dinary conditions. The following evidence indicated the validity of this assumption. Values of at 817° K using toluene-to»alkyl molar ratios between 60 and 120 showed little variation. Similarly values of k2 at 916° K with the same ratios showed little variation. However, as shown in Fig. 9, the value of ki (Table ^-) fell sharply when the toluene-to-alkyl molar ratio was decreased below 60. Values for k2 were similarly affected. Additional gas chromato graphic analyses have shown th a t the apparent decrease was due in part at least to the formation of propane, propylene, ethylbenzene, and xylenes. Analysis for butanes could not be made at that time, but these were probably formed. The Arrhenius plots shown in Fig. 8 were plotted using runs with toluene-to-alkyl molar ratios greater than 60. The simple linear nature of these plots supports the method of calculation used. The curves may be represented bys logio ki (sec-1) = 15.51*- (59,500/2.303RT) log10k2 (sec-1) = 7.9^- (35,M0/2.303RT) at 13.0 mm pressure. No other plausible explanation of the results could be found. The values of ki and k2 were both extremely sensitive to the nature of the surface in the reaction zone. TABLE h o % Si pH •H M ■s p P «5 •H P O 8 68 pce vesl us 81 K. 801° t a runs essel v packed 0 g 9 Vaiton o r e c tnt wih h mlr i tio a r molar the ith w ts stan n co te ra of n ariatio V 9* ig. F f ol t al . upce vesl us 87 K; 817° t a runs essel v unpacked 0 l. y lk -a -to e n e lu to of •*< L og _ 7.6 t f A To U 8 4 S A lOO AO SO 40 O I / / t l c Ctol/ / * * * * * 69 70 Admission of limited quantities of air to the conditioned vessel between runs resulted in approximately a 10Q# in crease in ki and a 200# increase in k2 even after pumping over a period of *f8 hours. Approximately 3 to h- runs were required to bring the values of the rate constants back to those normally observed in the conditioned vessels. Using a conditioned packed vessel with a surface-to- volurae ratio 12 times that of the unpacked vessel gave values of k^ 2.0 times and values of k2 1A times those ob served in the unpacked conditioned vessel. The percentage of heterogeneous reaction was calculated in the following manner. A value of k^ for the unpacked vessel was chosen at about the mid-point on the Arrhenius curve and the corres ponding value of k^ in the packed vessel (0.10 and 0.20 res pectively). The 0.10 increase in ki (unpacked vessel) was due to an increase of 11 in the surface-to-volume ratio. Thus the Increase per unit surface-to-volume ratio was 0.10/11 a 0.009. The percentage increase in k^ was 0.009/0.10 X 100# - 9#t and this was due to the heterogen eous contribution. It was concluded therefore that in the conditioned unpacked vessel the first bond rupture was pre dominantly a homogeneous process with a 9# heterogeneous contribution. In the same manner, the second bond rupture was a predominantly homogeneous process with a *+# hetero geneous contribution. Both ki and k2 depended on the total pressure in the system, although the dependence of k* was very slight 71 (Fig. 10), and was similar to the pressure dependence of trimethylblsmuth The pressure dependence of k 2 was similar to that observed for dimethylraercury and dimethyl- cadmium £^J and dimethylzinc J (Table 5 and Fig. 11). The reactions were investigated under conditions such that the rate of energy transfer was not sufficient to maintain the high pressure rate constant. Therefore based solely on unlmolecular pressure effects, the value of A 2 was ex pected to be of the order of 1011 to lO1^ sec"1. However, the observed value (A 2 = 8.71 X 10^ sec"1) was much lower than expected. This was presumably due to a change in mul tiplicity from the triplet to the singlet state as the second methyl radical was released from the trimethylgallium molecule. The pressure dependence of ^aAr^ Is shown in Fig. 12. The fall-off with increasing pressure was similar to that previously observed with the data obtained in similar studies with other metal alkyls studied **, 6_7, and was attributed to the third body requirements of the methyl radical recombination reaction. The ratio kaAr^ decreased at higher pressures due to the greater number of collisions to remove the energy of the excited ethane formed and there fore a lesser extent of redlssociatlon occurred. 72 O 10 1 0 30 Pressu re Cm») Fig. 10s Variation of rate constants with pressure for trimethylgallium (817° K) and dimethylgallium (91^° K). Subscripts denote the number of runs averaged to obtain the given point. 7 3 TABLE 5 Pressure Dependence of the Metal Dimethyls Dimethylmercury (8l6° K) Log Pt 1.01 1.21 l A l Log ki T. 56 T.68 T.80 Diraethylcadmium (825° k ) Log Pt Q.7k 0.80 1.19 1.3^ 1.39 Log kt T.58 1.52 T.80 T.87 T.90 Dimethylzinc (870° K) n j Log Pt 0.86 1.10 1.21 1.3^ 1A2 1A 5 Log kt T.13 T.25 T.3^ T.39 IM T.50 Dimethyl gal Hum (91^° K) Log Pt 0.79 0.96 1.12 1.27 1A8 Log kt T.28 T.30 TA5 T.60 T»55 T.70 7 * «D *9 77 * 75 <& o ^ 73 o ' / /•/ 0.6 0-8 to A 2 / # t6 L o g P Pig. H i Variation of rate constants of various dimethyl metals with pressure. 0 dimethylcadmium (825° K); 0 di- methylmercury (816° K); t dimethylgallium (91M-0 K); 0 dimethylzinc (870° K). 75 2-7 3 . / 30 “O 0 to to 30 P ressure (mm) Fig# 12* Variation of fcaAr^ with pressure. Upper curve - 817° K (first bond region)} lower curve - 911*0 K (second bond region). Subscripts denote the number of runs aver aged to obtain the given point. 76 The Pyrolysis of Trlmethvllndium The pyrolysis of trimethylindium was studied in the toluene carrier flow system from 550° K to 781° K using total pressures from 6.0 mm to 33*5 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, propane, and ethylbenzene formed, and in a number of cases by direct indium analysis. The complete experimental results are given in Tables 6, 7, and 8. They may be discussed in terms of the fol lowing mechanism: In(CH3 )3 In(CH3 )2 + ch3 ( 1) In(CH3)2 In(CH3) + ch3 (2) In(CH3 ) In + ch3 (3) n InCH3 (InCH3)n 0 0 CH3 + C£H5-CH3 C6 H5-CH2 + CH1+ (a) 2 CH3 CH3-CH3 (r) 2 C6Hj-CH2 (c6h5-ch2)2 (5) The abstraction reaction (a) is a composite reaction pro ceeding mainly as written but with a small percentage of abstraction from the ring. 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The characteristic break at 67# theoretical yield of methyl rad icals released indicated that below 670° K reaction ( 2) fo l lowed rapidly after reaction ( 1), but reaction ( 3) did not occur to any appreciable extent. Rate constants below this temperature (ki) have therefore been calculated assuming that two methyl radicals were released for each trimethyl- lndium molecule undergoing decomposition. Above 680° K, all of the trlmethyllndium was converted to methyllndium plus two methyl radicals in a very small fraction of the contact time. Rate constants in this region (k3) have therefore been calculated assuming that the fraction of the third bond ruptured was given byt (moles of methyl radicals) - (2 moles of trlmethyllndium). vmoles of trimethylindium) Although the break in the Arrhenius curve of ^a/kr^ was indicative of the process outlined, Independent tests have been made to verify the mechanisms a) In 18 of the runs, the contents of the acetone-dry- ice trap located at the outlet of the furnace were analyzed for indium. If reaction (3) is responsible for the removal of methyllndium, then above 670° K a ll of the Indium should be deposited in the reaction zone. Table 9 shows that over the entire third bond region only traces of Indium reach the acetone-dry-ice trap. Below this temperature the quantity 81 \ \ eo > » "'Xs © 13 /•# /S f-t b7 AS fOOO/T Fig. 13* Arrhenius plots for the decomposition of methyl- indium and trimethylindium and the reaction of methyl radicals with toluene. 0 rate constant based on gas anal ysis; t rate constant based on metal analysis; % ^a/kr ** Subscripts denote the number of runs averaged to obtain the given point. 82 TABLE 9 Runs with Indium Analyses Temp 1Percent Decomposition Trap kg Rm Gas Metal Analysis ( K) (JO (JO (JO (sec*1) (sec*1) Third Bond Regions 753 83.3 1.5 729a 98.3 1.5 726 57.9 3.9 720 72.8 0.9 697 63.1 2.5 681* **5.3 1.2 F irs t Bond Regions 6¥*a 91.7 73.5 26.5 0.9V5 0.510 637a 6V.8 1*6.5 53.2 0.533 0.320 633a 77.8 51.8 V8.1 0.606 0.298 62Va 50.3 36.9 63.7 0.292 0.183 623a 57.2 VO. 7 59.0 0.338 0.209 620a 19.7 13.3 85.7 0.219 0.138 613 Vo.o 58.0 613 12.0 87.8 61’ 11.0 90.1 610 15.0 81.0 59** 16.3 83.0 556 1.2 98.0 a runs in an unconditioned vessel of indium found in the trap was in agreement with the pro posed mechanism. b) In 7 of these 18 runs a clean pyrex vessel was used. In each of these 7 runs the indium content of the reaction zone was analyzed. The values of k]^ calculated assuming moles of indium in the reaction zone equals moles of tri- methylindium decomposed are shown in Fig. 13. The agreement with ki values in a seasoned vessel calculated assuming two methyl radicals released for each trimethylindium decom posed was excellent. c) The rate constants for the reaction in a clean ves sel based on gas analysis lie above the Arrhenius curve. The difference in the extent of reaction compared to the metal analyses was a result of reaction on the unconditioned surface. The most probable surface reactions consistent with the experimental results were the surface decomposition of methyllndium to give indium metal plus a methyl radical and the surfaoe decomposition of trlmethyllndium. The first of these reactions lead to a decrease in the quantity of methyllndium deposited in the reaction zone. Hence in an experiment in an unconditioned vessel in which 1.0 raM of methyllndium would have been deposited in the reaction zone in a conditioned vessel, addition of bromine vapour to the hot reaction zone (637° K) while still under vacuum pro duced only 0.3V mM of hydrogen bromide and a quantity of polymethylene quantitatively in agreement with the reactloni 8>f The 0.66 mM of methylindium apparently lost by the surface reaction was in good agreement with the additional methyl radicals detected in the gas analysis (0.58 mM). d) In a run in the unconditioned vessel in the third bond region, the vessel was removed from the furnace under vacuum to visually inspect the methyllndium polymer. It appeared as a white non-metallic solid coating the entire surface of the reaction zone. To determine the indium con tent, concentrated hydrochloric acid was admitted to the reaction zone and reaction with the methyllndium polymer was observed. After the indium chloride solution was re moved, a thin white coating appeared to remain on the sur face. Addition of 20 % hydrofluoric acid almost immediately caused the coating to peel from the surface. This coating again was polymethylene, and was probably formed by the reactions 3n HC1 + (InCH3)n ------n InCl3 + 2n H2 + (CH2)n Starting with a clean vessel, both ki and decreased over several runs to a fixed minimum value in what was sub sequently called a conditioned vessel. If air was admitted to the reaction vessel between runs, an additional 2 to 3 runs were required to recondition the surface of the reac* tion zone. The percentage of heterogeneous reaction was estimated by carrying out a series of runs in a packed ves sel with a surface-to-volume ratio 12 times that of the unpacked vessel. Because of the large surface area, com plete conditioning was not obtained, but after a series of 8 ? runs ki was reduced to about 2.2 times its value In the un packed vessel and k3 was reduced to about 1.3 times its value in the unpacked vessel. Therefore, in the unpacked vessel used in this work, the reaction was at least 90 % homogeneous in the f i r s t bond region and a t le a st 97Jf homo geneous in the th ird bond region. Both ki and k3 depended on the total pressure in the system, although the pressure dependence of ki was very slight (Fig. 1*0. The slight pressure dependence of ki was was similar to that observed for the thermal decomposition of trimethylgallium £37_7 trimethylbismuth JT6J. As shown in Fig. 15, the pressure dependence of the thermal decomposition of methyllndium was somewhat less than that of methylzinc This was presumably due to the large tem perature difference at which these decompositions occurred. The pressure dependence of ka/kr^ is shown in Fig. 16. The fall-off with increasing pressure was similar to that previously observed ^"1, 6, 37.7, and was attributed to the third body requirements of the methyl radical recombina tion reaction. The ratio ka/kri decreased at higher pres sures due to the greater number of collisions that deacti vated the excited ethane formed and therefore a le sse r ex tent of redissociation occurred. As shown in Fig. 17, the value of ki fell sharply when the toluene-to-alkyl molar ratio was decreased below 150 (Table 10). Values for k3 were similary affected. The Arrhenius curves shown in Fig. 13 were therefore plotted 86 2-9 o- °o' 2-7 O O ^ 2-5 o o * 4 0 /O 20 30 P ressure (mm) Fig. l^-i Variation of rate constants with pressure for trimethylindium (610° K) and methylindium (7M*-0 K). Sub scripts denote the number of runs averaged to obtain the given points. 8 7 t b 7 6 o W -J A 2 t.0 OS t'O t-Z t+ t'6 Loo P Fig. 15i Variation of Bata Constant with Prasssura for tha Matal Mathyls. 0 Mathylindium at 7M*o K; • Methylsinc at 1056° K. Subscripts danota tha numbar of runs aYaragad to obtain tha glvan point. 8 8 l ■" .i """ * o' 1 7 /6 ; \ \ O—o bS o 2 2 - \o — 2-/ \ rN > 20 ° > ° o ” i J_____ 1__ 0 to 20 30 P r e s s u r e ( m m ) Pig. 16* Variation of ka/kr^ with pressure. Upper curve - 610° K (first bond region); lower curve - 7Mf° K (second bond region). Subscripts denote the number of runs aver aged to obtain the given point. i. 7 Vrain f ae osat wt mlr ato of tio ra molar with constants rate of Variation 17: Fig. oun-oakl 0 us 63 K; 613° t a runs 0 toluene-to-alkyl. Loo k 28 mm tz o ZO 0 400 300 ZOO too % us 69 K. 629° t a runs 89 90 using only rate constants obtained in runs where the toluene- to-alkyl ratio was greater than 150. The simple linear nature of these plots supports the method of calculation used. The curves may be represented byt logio kx (see"1) » 15.72 - 0*7,200/2.303RT) logi0 k3 (sec-1) s 10.91 - (38,700/2*303RT) TABLE 10 Variation of k with Gtol/Ca]jc at 13«0 mm Tamp to InHa3 CH^ C2H5 (»2®f kl , £1 2 1 * (°K) (sao) (fflM) (mM) (mM) (mM) (sac ) °.lk 629 2.005 0 .6kl 0.076 0.0009 O.OOO^f 0. 1^7 66.b 629 2.090 0.665 0.187 0.1110 0.0020 0.2M* 196 629 2.000 0.9**8 0.312 0.1610 0.0000 0.290 257 613 1.909 1.600 0.091 0.0683 0.0011* 0. 0^9 Wl.O 613 2.110 1.^69 0.106 0.0916 0.0012 0.057 59.0 613 2.1*f0 0.82** 0.163 0.0862 0.0000 0.123 205 613 2.050 1.112 0.269 0.1050 0.0010 0.138 386 a molar ratio 91 The Pyrolysis of Trimethylthallium The pyrolysis of trimethylthallium was studied in the toluene c a rrie r flow system from ** 58° K and 591° K using total pressures from 5*6 mm to 33*0 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, propane, and ethylbenzene formed, and in a number of cases by direct thallium analysis. The complete experimental results are given in Tables 11, 12, 13, and l*f. They may be discussed in terms of the following mechanisms ti( c h 3)3 T1(CH3)2 + ch 3 ( 1) ti(c h 3)2 T1(CH3) + ch 3 (2) t i(ch 3) T1 + ch 3 (3) CH3 4- C6H5-CH3 C6H5-CH2 + CHlf (a) 2 CH3 ch 3-ch 3 (r) 2 C6H5-CH3 (c6h 5-ch 2)2 0 0 The abstraction reaction (a) was a composite reaotion proceeding mainly as written but with a small percentage of abstraction from the ring. The ethylene and the hydrogen observed in very small amounts (usually less than 0.05JO result from the reactionsi CH3 4* C2H6 ----- ► C2H5 + Cfy <*) C2H5 C2H|+ 4 B (6) B + C6H5-CH3 ----- * C6H5-CH2 + H2 ( 7) In runs with low toluene-to-alkyl ratios, propane, ethyl- benzene, and xylenes observed in small amounts result from the reactions! 92 O'CM O J - O rn J- OO Un \ooi• •••••••••• mo'Ow'riO'ooj-oo O 00 CO U. ITN \r\ NO n ro ro (\1 H| IftO OvRftlJ^nOvflOtK H i O ^ w „5d ®O OrONvOlroNMOOO••••••••••• « CMHHOOOOOOOO IfV Q Jf o to Jxo o mIs g o o % o• o•o o o o o• o• o o © 00 H w 8 H « O w o § 3 ” ooooooooooo iH■P'd ® S3 O ■P® -HP • •••••••••• •S3 ooooooooooo £8 o vO p"v UN W HOpvOONJ-ONqu>. . VO ON CM J r VTN - - m . . , _ 00 H ro Cv. H H vO CO fO Uv fO rt rl rl *8 • •••••••••a w«o h OHHOOOOOOOO ■H O R« s O Uv O O N N ® O' J O 01 1! Ud \V i&&l8gS88gg••••••••••• OOOOOOOOOOO ea«* - ft JS*m*SU* ohhooohhhoh O ®n W—* ooooooooooo mmrnmrorororornmrn• • ••••••••• ® I HHHHHHHHHHH ■3 a. 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O J t © O VTN H o © • • • • • • • • • M H O O CM CM■H O O O \TN td H H © H CO 'O O & 1 8 8 8 8• «• 88• • • • ~ o o o o o o o o o no „ U w • ••••• o o o o o o H ©W | S s <9 £tS'© © o• o••••• o o o o •P© flo StI «H +> y) O S CM O r o n o CM NO h «rt Nfi (N <*"* n o J - n O O H RS 3 * 8 8 § * § ! * ? • ••••• w 13 o o o o o o o o o © £ n o rO Q O UNH O ® s no 8 o fO ^0 XJw j j ^ NO O ^ \r\ 00 H • • • ••••• H W O o o H O O O O O <2000 O O O O O O © S • • • • ••••• A B no no no no no no no no ro v-* H r l H H H rl rl rl rl ^ Q r o O O CMC^ 4^ © no ® ^ CO CO III M • • • • ••••• w r< O O O O rl rl rl O O OOvfflOi I? - no ITN no i-I O' CO J- IfN J- \TN \TN \fN \TN Jfr jJ- © ja o «o 97 CH3 + C2H5 CgH^-C^ C8) ch 3 + c6h ?- ch 2 -► c6h 5- ch 2- ch 3 (9) CH3 + ^ CH3-C^Hif-CH3 (10) The Arrhenius plot of fca/kr^ shown in Fig. 18 shows no characteristic break at 33# or 67# theoretical yield of methyl radicals indicating that at all temperatures reac tions (2) and (3) follow rapidly after reaction (1). Thus the rate constants were calculated assuming that three me thyl radicals were released for each trlmethylthallium mol ecule undergoing decomposition. Although the continuity of the Arrhenius curve of ka/kp^ was indicative of the process outlined, independent tests have been made to verify the mechanisms a) In most runs (see Table 15)» the contents of the acetone-dry-lce trap located at the outlet of the furnace were analyzed for thallium. Over the entire temperature range of decomposition, the thallium found in this trap was equal to the quantity of undecomposed trlm ethylthallium ex pected if each alkyl molecule that decomposed liberated three methyl radicals. b) In 10 runs, the contents of the reaction vessel were analyzed for thallium. In all cases the quantity of thallium deposited in the reaction zone was in agreement with the postulated release of three methyl radicals. To insure that the deposit was actually thallium, 0.082 grams of the deposit was scraped from the reaction zone while in an inert atmosphere and analyzed for thallium. 19.0 mis of 98 O \ *• v 04 o\© 0*6 0 4 w io o o / t Fig. 18s Arrhenius plot for the reaction of methyl radi cals with toluene. • runs in the unpacked unconditioned vessel; 0 runs in the packed unconditioned vessel; 0 runs in the unpacked conditioned vessel; • runs in the packed conditioned vessel. 99 TABLE 15 Runs with Thallium Analyses Temp Percent Decomposition Trap kg© km Gas M etal A n aly sis (°K) oo {%) <*) (s e c - 1 ) (s e c - 1 ) 593-h i 95.2 98.5 3.^8 l+. 8 »+ 571m 90.5 91.6 2.60 2.65 571m 85.3 88.9 1.99 2.28 568m 7^.0 71.6 1.36 1.27 567m 7*+.2 25.3 1.52 560m 58.2 60.5 38.7 0.955 1.020 558m 86.7 87.6 1.57 1.80 ?+3i 86.3 11.0 2.05 * 3 m ^3.9 **5.0 0.565 0.585 5lf2m *+7.*+ »+5.0 5*+.2 0.718 0.671 5131 50.0 ^7.3 0.651 5o in i 6.8 8.0 0.069 0. 08 ^ 5 ° ° m 9.5 9.3 89.8 0.099 0.097 8.6 91.8 0.087 *+911 22.9 77.1 O.23I+ lt'86m 5.9 93.2 0.05*+ 10.5 39.*+ 0.095 8.8 89.5 0.082 k7hu 1.3 1.8 97.9 0.012 0.016 ^ O i n 2.0 95.0 0.019 W 6n 16.*+ 82.2 0.212 I runs in the unpacked unconditioned vessel II runs in the packed unconditioned vessel III runs in the unpacked conditioned vessel 100 0.02 M EDTA were required giving a thallium analysis of 99.8#. No evidence was found for the formation of polymer of the type (TlCH 3)n, as found in the pyrolysis of tri- methylgallium or trimethylindium. Starting with a clean vessel (I), the rate constants did not decrease over several runs to a fixed minimum value as in the case of trimethylgallium or trimethylindium. On the other hand, the rate constants remained at a constant value; near 95% decomposition in successive runs, the rate constants were 2.2*+, 2.28, and 2.11+ sec"1. One of these runs would have deposited enough thallium to change the surface, however no effect due to coating the surface with with thallium was observed. In another series of runs, small amounts of a ir accidentally introduced into the reac tion zone between runs produced no observable effect on the rate constants. The experimental data under these condi* tions (unconditioned and unpacked vessel) is given in Table 11 and constitutes curve Z in Fig. 19. The percentage of heterogeneous reaction was estimated by carrying out a series of runs in a packed vessel (II) with a surface-to-volume ratio 12 times that of the unpacked vessel I, and the results are given in Table 12 and consti tutes curve II of Fig. 19. The rate constants obtained using vessel II were a factor 3*7 greater than those ob tained in vessel I. The overall reaction in vessel I was therefore apparently about 25# heterogeneous. In an attempt to reduce the amount of surface reaction, 101 'a • * 7 5 r \ o \8 \ A7 18 t-9 ZO 27 22 IOOO/T Pig. 19* Arrhenius plots for the deconposltion of tri- methylthalliun. 0 runs in unpacked unconditioned vessel (curve I); 0 runs in packed unconditioned vessel (curve II); 9 runs in unpacked conditioned vessel (curve III) (0 based on metal analysis); •runs in packed conditioned vessel (curve IV). Subscripts denote the number of runs averaged to obtain the given point. 102 the unpacked vessel was Initially treated with hot 50 % hydrofluoric acid for 10 minutes. This treatment was re peated for at least 2 minutes between each run. The experi mental results are given in Table 13 and constitute curve III of Fig. 19* The rate constants In vessel III could never be reduced below this curve even by longer treatments with hot 50# hydrofluoric acid. Therefore throughout this work vessels treated as described above are termed condi tioned vessels. To estimate the percentage of heterogeneous reaction in vessel III, a packed pyrex vessel (IV) with a surface-to- volume ratio 9 times that of vessel III was treated with hot 50% hydrofluoric acid fo r 10 minutes. This gave a rate constant high by a factor of 13* Further conditioning with the hot acid reduced the rate constants to approxi mately a factor of times those obtained in vessel III. These results are tabulated in Table l1* and constitute curve IV in Fig. 19. These results Indicated that the reaction in vessel III was approximately 1*4# heterogeneous. Comparison of curves I and I I I indicated th a t the reac tion in vessel I was about 79# heterogeneous. This result was obtained by the following calculation* if the rate constant k in vessel III was 0.100 units and lb% of th is was due to the heterogeneous component, the the homogeneous component was 0.086. The k in vessel I was 0A00 and its heterogeneous component OAOO - 0.086 - 0.311** Thus the percentage of heterogeneous reaction in vessel I is 103 0.3lV0.»K)0 X 100# = 79#. The above calculated large percentage heterogeneous reaction is consistent with the greater than ^5# hetero geneous reaction that would be Indicated by comparison of curve I with the initial runs in the partially conditioned packed vessel (vessel IV before it was fully conditioned). The low estimate of percent heterogeneous reaction in vessel I obtained by comparison of runs in vessels I and II was probably due to the fact that vessel II had been washed with hydrofluoric acid before being stored at the conclusion of previous work. The pressure dependence of ^a/kp^ ls shown in Fig. 20. The fall-off with increasing pressure was similar to that previously observed with values obtained in similar studies with trimethylgallium, trimethylindium, and other metallic alkyls studied *f, 6 J and was attributed to the third body requirements of the methyl radical recombination reac tion. However, at the low temperatures at which trlmethyl thallium released methyl radicals into the toluene stream, the fall-off was less than at higher temperatures* Less thermal energy was available for the methyl radicals and thus there was less energy in the ethane formed and the tendency for the methyl radicals to fly apart after recom bination was reduced. The ratio ^aAr^ vas higher at lower pressures due to the fact that there were less collisions to remove the energy of the excited ethane formed and there fore a greater extent of redissociation occurred. 10>t 10 0*6'L ______I______I______I______J o to 1 0 so 00 PRESSURE (mmt) Pig. 20* Variation of ^aAr^ with pressure at 528° K. 0 represent individual runs; • point taken from Fig. 18. 17 O 7*6 o ^ 75 O to 20 30 4 0 Pressure M Pig. 21* Variation of rate constant with pressure for trlm ethylthallium a t 528° K. UNIVERSITY OF WINDSOR LIBRARY 1 0 5 The rate constant k depended on the total pressure In the system, although the pressure dependence was very slight (Fig. 21). This slight pressure dependence was very similar to that observed for the thermal decomposition of trimethyl- gallium of trimethylindium. The overall reaction in the unpacked conditioned vessel may be represented by the equation* log10 k (sec*1) 5 10.2 - (25,800/2.303HT) However, at low temperatures the heterogeneous component consisted of 16# while at higher temperatures the hetero geneous component was only 13jf. The homogeneous reaction in the unpacked conditioned vessel may be represented by* lo g 10 k (s e c - 1 ) S l o . k - (26,^00/2.303RT) CHAPTER V DISCUSSION Reaction of Methyl Radicals with Toluene The values of ka/kr^ have been calculated using the equations to, - — ~oi». c«t— x,— x I kpT [moles C 2H6 + C2HU]* 32 Z0 0-8 0-4 1000/T Fig. 22i Arrhenius Plot for the Reaction of Methyl Radicals with Toluene. 9 Dimethylzlnc; 0 Dlmethylmercury and Di- methylmercury; • Trimethyl gallium; 0 Trimethylindium; 0 Trlmethylthallium. 109 the extent u* redissociation will increase as the tempera ture is increased. Thus the amount of ethane formed was smaller than i t should have been and large values of ka/kp& were obtained. The Toluene Carrier Technique The thermal decomposition of trimethylantimony has been studied by the toluene carrier technique /~ 6_7 , but the decomposition was not simple. Even at the highest tempera tu res, the yields of methane and ethane f e ll fa r below the amount th at would be expected i f a l l of the alkyl decomposed. The first order rate constant based on either gas or metal analysis decreased with increasing concentration of the tri- methylantimony. This deorease was probably due to some sort of back reaction as the toluene-to-alkyl ratios employed (*+0 to 50) probably did not afford complete removal of the radicals on formation, and the inoreased difference of rate constants based on gas and metal analyses was probably due to incomplete analysis or the formation of a polymer of the type ( 8 bGH3>n. Much less complexity was obtained in the thermal decom positions of trimethylgallium, trimethylindium, and tri methyl thallium, as higher toluene-to-alkyl ratios were employed. I t was found th a t a t low toluene-to-alkyl ra tio s the rate constants decreased, and from the plot of rate constant versus the toluene-to-alkyl ratio, a minimum accep table toluene-to-alkyl ratio was obtained. 110 A series of runs were carried out using dimethylmer- cury as the radical source. At toluene-to-alkyl molar ratios of 7.6 and 9.5, the analysis of methane, ethane, ethylene, propane, and proylene yielded only 67% and 77 % of the theoretical amount of methyl radicals expected, respec tively. Analysis for ethylbenzene, meta-, ortho-, and para- xylenes yielded the remaining methyl radicals expected. With trimethylgallium and trimethylindium a similar apparent loss of products was observed; in these cases only 20% to of the lost products was found in the liquid analyses. The remaining loss was presumably due to some back reaction. Pyr.stolg, pjLLriffathylKftUAani No previous studies on the bond dissociation energies of trimethylgallium have been reported. The mean bond energy has been obtained by the reaction of trimethylgallium with iodine in benzene solution /[‘llJ% and by the combus tion of trimethylgallium with oxygen in a static-bomb calo rimeter The mean gallium-methyl bond energies from from these studies were 56.7 kcal/mole and 57*7 kcal/mole, respectively. However Long, using D/^CHj-H^ a 102.5 k cal/ mole, has recommended a value of 57.5 kcal/mole /"15J7. In this work, the experimental evidence indicated that the Arrhenius equations for the pyrolysis of trimethyl gallium and dlmethylgalllum were* logio *i (sec-1) « 15.51* - (59,500/2.303RT) lag10 k2 (see-1) • 7.9V - (35,V10/2.303BT) I l l respectively. From theoretical considerations, it has been shown that the experimental activation energy at the high pressure limit may be approximately related to the bond dissociation energy. Thus we may writes tyf(CH3)2Ga-CH3_7 « 59.5 kcal/mole as the rate constant for the pyrolysis of trimethylgallium was independent of pressure. The pyrolysis of dimethyls gallium was carried out in the pressure dependent region. Assuming 10 effective oscillators, D 2 s &2 4 2.5 kcal/mole, and we obtains D/T“CH30a-CH3_7 - 37.2 kcal/mole Since the sum of the three gallium-methyl bond strengths is 172.5 kcal/mole, by difference we obtains D/"Ga-CH3_7 = 75.8 kcal/mole Even as high as 1075° K, the methylgalllum did not de compose; rather a polymer of the type (GaCH3)n was formed. Assuming A s 1011 (which is reasonable because for methyl- indium A s lO10^ 1), the Arrhenius equation would be of the fonns iogiQ k3 (sec-1) s 11 - (75,800/2.303RT) Measurable decomposition of methylgalllum will occur when k3 is of the order 0.1 units. Solving for T, we obtain a value of approximately 1350° K. I f we assume A is of the order of 10^, we obtain a value for T of approximately 1650° K. In either case, the experimental conditions that would be required are beyond those afforded by the toluene 112 carrier technique. The Pyrolysis of Trimethylindium No previous studies on the bond dissociation energies of trimethylindium have been reported and only a tentative experimental value of the mean bond energy is available equal to 38*2 kcal/mole £VlJ* This value is in agreement with the estimated value kl t 3 kcal/mole obtained from the available data of the neighbouring metallic methyls* In this work, the experimental evidence Indicated that the Arrhenius equations for the thermal decomposition of trimethylindium and methyllndlum were* lo « i0 kj, (Me*1) ■ 15.72 - <^7,200/2.303RT) logic k3 (Me*1) * 10.91 - (38,700/2.30381) respectively* From theoretioal considerations, it has been shown that the experimental aotivatlon energy at the high pressure limit may be approximately related to the bond dissociation energy. The rate constant for the pyrolysis of trimethyl indium was independent of pressure so we may writes D/"(CH3)2ln-CH3_7 s **7.2 kcal/mole The pyrolysis of methyllndlum was carried out in the pres sure dependent region* Assuming 8 effective oscillators, D3 ■ E'3 + 1.3 kcal/mole, and we obtains D^In-CH^.y 5 *+0.0 kcal/mole Since the sum of the three indium-methyl bond strengths is ll*f *6 kcal/mole, by difference we obtains 113 D/fCH3ln-CH3-7 * 27A kcal/mole. Tfae. PmilZsis.P0^1peJbh£lthalllupi No previous studies on the bond dissociation energies or mean bond energy of trlmethylthallium have been reported. From the known total metal-methyl bond strengths of the neighbouring elements, a value of 6 5 1 5 kcal/mole was es timated for trlmethylthallium. In this work, the experimental evidence indicated that the Arrhenius equation for the pyrolysis of trlmethylthal- lium vast logic k - (26,WOO/2.303RT) From theoretical considerations, it has been shown that the experimental activation energy at the high pressure limit may be approximately related to the bond dissociation energy. The rate constant for the pyrolysis of trlmethyl- thallium was Independent of pressure so we may writes D /a’(CH3)2Tl-CB3_7 ■ 26.If kcal/mole Unfortunately, nothing oould be said about the remaining two bonds except that D 2 plus D3 are approximately equal to 39 4 5 kcal/mole where D 3 would be expected to be stronger than D 2 because of the tendency of thallium to bond chemi cally in the monovalent state. The thermal decomposition of trlmethylthallium was very surface dependent (greater than 79 % heterogeneous reaction in a unpacked unconditioned vessel). Trimethylgallium and trimethylindium decompositions would condition the reaction lib vessel. The rate constant was reduced to a fixed value after 3 to 5 runs. On the other hand, the thermal decom position of trlmethylthallium would not condition the vessel between runs when starting with a unconditioned vessel. However, starting with a conditioned vessel, successive runs producing an increasing deposit of thallium metal on the surface raised the rate constant to the level of the uncon ditioned vessel. Consequently, conditioning with hot 50% hydrofluoric acid was required between runs to obtain reproducible results in the conditioned vessel. Moreover, if the amount of trlmethylthallium used in a run was 0.5 to 2,0 mM, no variation in the rate constant was observed sig nifying th a t the maximum amount of alkyl used in a run did not deposit enough thallium to significantly Increase the rate. Therefore the rate oonstants observed in the indivi dual runs were a true Indication of the decomposition in the conditioned vessel. gmnatioM for, ftarthw The available bond dissociation energies (at the high pressure lim it) and mean bond energies of covalent metal- methyl bonds are given in Table 16. Values for the methyl derivatives of some of the non-metals af Croups IV to VII are Included for comparison. All of the mean bond energies in Table 16 have been calculated from the appropriate heat of formation at 25° C, the heat of atomization of the parent element, and 115 TABI£ 16 Metal-Methyl Bond Strengths to ta la energy Dl d 2 re f. Group I lb i (CH3)2Zn 82.9Z"2-7 >*1.5 »*9.0 33.9 fU (CH3)2Cd 66.2/"3j7 33.1 ** 8.8 17.^ P*J (CH3)2Hg 58.9 C& 29.5 53.7 5.2 Group I llb t ( C H ^ l 61.9 78 — C*J (CH3)30a I??- 5r^j 57.5 59.5 37.2 75.8 (CB3)ifSl 28 k.fflkj 71.1 78.8 •««ie -----£V*J (CB3)lfGe (CltylfSn 208A/>3_7 52.1 55.0° ■ see m m m m (CH3>»JPb 139.6,fM*_7 3^.9 ----- mmtmm Group Vbi (ch 3)3p 195.9Z>5_7 65.3 m m m m .... (ch 3)3a . 15^Aif9 J 51.5 5^.6 — - rioj (CH3) 3Sb 1 & 9 .1 /V **9.7 57.0 -----CBJ (ch 3 )3b i io i. ?ClJ 33.7 M*.0 —— -----CBJ Group VIbt (CH3)28 1**0.6/"W6_7 70.3 73.6 57.0 P*J (ch 3)2s « mmmmmmmmmmm m m m m (CI^^Te mmmmmmmmmmm Group V llbi gh 3c i Bz.ifUej 82.1 82«1 CH3Br 68.9Z^9_7 68.9 68.9 CHjI 5**.*♦/" 50 J 5VA 5WA jy of the metal-methyl bonds In koal/mole §kcal/mole ralue 116 T>CCYlyKj s 102.5 kcal/mole. The value of Di for dimethylzinc is obtained by correc ting the 16 mm value of **7.2 £lJ by adding 1.8 kcal/mole. Dg is obtained by adding 1*3 kcal/mole to the 16 mm kinetic value or by difference from thermochemical data; this latter value is probably the more correct value. As Di for trimethylaluminum is about 78 kcal/mole, the toluene carrier would also decompose appreciably. The use of benzene as the carrier would be better because benzene decomposition gives mainly ethylene and no methane. The mean bond energy of trimethylthalllum needs investigation. The mean bond energy of tetramethylgermanium needs in vestigation. The tetramethyls of Oroup IVb should be stu died by the toluene carrier technique (except tetramethyl- slllcon - benzene as carrier might be better), and if dif ficulties arise the diohlorodlmethyls may give good esti“ mates (maximum values) of the first bond energies. Although trlmethylantlmony has been studied by the tolu ene carrier technique, it should be redone at much higher toluene-to-alkyl ratios. Trimethylphosphorous and trlmethyl- arsenlc should also be studied in this manner. The mean bond energies of dlmethylselenlum and dlmethyl- tellurlum need Investigation. The dimethyls of sulphur, selenium, and tellurium should be studied by the toluene carrier technique. REFERENCES 1. S. J . W. PRICE and A. F . TROTMAN-DICKENSON. Trans. Far. Soc. 53, 1208 (1957). 2. L . H . LONG and R. G. W. NORRISH. Trans. Far. Son. it5, 1159 (19*4-9). 3. A. S. CARSON, K. HARTLEY, and H. A. SKINNER. Proo. Roy. Soc. A195. 500 (19*4-9). b. S . J . W. PRICE and A. F. TROTMAN-DICKENSON. Trans. Far. Soc. 53, 939 (1957). 5. K. HARTLEY. H.O. PRITCHARD, and H. A. SKINNER. Trans. Far. Soc. S i, 1019 (1950). 6. S. J . W. PRICE and A. F. TROTMAN-DICKENSON. Trans. Far. Soc. 5Jt, 1630 (1958). 7. L. H . LONG And J . F. SACKMAN. Trans. Far. S o e . 50* 1177 (195*4-). 8. L. H. LONG and J. F. SACKMAN. Trans. Far. Soo. 51, 1062 (1955). 9. L. H. LONG and J . F. SACKMAN. Trans. Far. Soc. 5£i 1201 (1956). 10. P. B. 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Nature, 170. 320 (1952). VITA AUCTORIS Borns October II, 1938) Windsor, Ontario, Canada. Son of Hr. George and Mrs. Anna Jacko. Primary Schoolss St. Claire, St. Bernard, and St. Angela Schools, Windsor, Ontario, Canada. Secondary Schools Assumption High School, Windsor, Ontario, Canada. Academic Courses 1952 - 1957* University! Assumption University of Windsor, Windsor, Ontario, Canada. 1957 - 1961. Degrees Bachelor of Science in Honours Chemistry and Physics awarded in 1961. University of Windsor, Windsor, Ontario. Canada. 1961 - 196^. Research and Teaching Assistant. Awardss 1962s National Research Council of Canada Stu^ dentship. 1963 s National. Research Council of Canada Stu dentship. Publicationss The Pyrolysis of Trimethylgallium, Canadian Journal of Chemistry, *fl, 1560 (1963). The Pyrolysis of Trimethylindium, Canadian Journal of Chemistry, *£2, 1198 (196*0. 120 121 Professional Societies* Chemical In s titu te of Canada. Association of the Chemical Profession of Ontario. Marital Status* Married June 8, 1963, to Mary Helen Boldizar. One child* Marcy Anne.