Using diniethylzinc, dimethylmercury, and trimethylbismuth as sources of methyl radicals, values of kl/k2112 have been calculated from 338 to 610 "C over the pressure range 4.5-204 mm. M is predoniinantly toluene. The observed pressure dependence of reaction [2] is in agreement with that found when M = benzene, but is somewhat greater, and the fall-off occurs at higher pressures, than for ethane dissociation. However, reasonable agreement is obtained if it is assumed that the efficiency of toluene as a third body in reaction [2] is abo~lt 1110th that of ethane.Extrapolation to infinite pressure, whereit is assumed that E2 = 0 and A2 = 1013.34 cm3 mole-' s-', gives E, = 8.0 0.3 kcal mole-' and A , = 101'.07 cm3 mole-Is-'.

. Can. J. Chem. 54, 2981Chem. 54, (1976.The pyrolysis of C6H51 has been studied by the toluene carrier technique over the temperature range 861-955 K using contact times of 0.54-3.28 s and total pressures of 2.5-4.13 kPa. Percent decomposition based on analysis for residual C6HjI ranged f r o n~ 5.6-93.3(t. Only trace quantities of 1 2 were observed and when HI mas trapped o~l t the only other gaseous products were small quantities of hydrogen and methane in about a 2:l ratio. Within the limits of the experimental method the decon~position was found to be homogeneous and first order.

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The thermal decomposition of Hg(CH3), has been studied in a toluene carrier flow system over the prcssurc range 4.5 to 323 nlm at temperatures of 422 to 527 "C. The Arrhenius equation for the pressure independent region, k = 5.5 x 1015 exp (-57 500/RT) s-I is in excellent agreement with earlier work on the fully inhibited decon~position at lower temperatures. The region of fall off of the unimolecular rate constant is in agreement with a classical Kassel calculation using s = 16-18, but the rate of fall off requires the use of a curve with s = 3, displaced five log units to the left. This is consistent with the previous results for the dissociation of ethane into tmo methyl radicals and is further evidence of the inability of the classical Kassel equation to represent the behavior of systems with high pre-exponential factors.

The recombination of methyl and benzyl radicals has been studied over the temperature range 529 t o 799 OK. The Arrhenius parameters for the recombination reaction are log A (cc mole-Is-') = 11.20, E = 0.20 kcal mole-'. The frequency factor a t 1 000 OK for the reverse reaction, the dissociation of ethyl benzene, is calculated to be log A (s-1) = 14.9. A value of 70.5 kcal mole-' has been estimated for D(CoHbCH2-CHa).