The reactions of methyl radicals with chloromethanes

The reaction of methyl radicals with CCl 4 and CCl 3 Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di‐tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH 3 CCl 3 , formed via the combination of methyl and trichloromethyl radicals. From these investigations Arrhenius parameters for the reactionshave been determined:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = 10^{8.8 \pm 0.3} {\rm exp - }\left({\frac{{{\rm 10}{\rm .1} \pm {\rm 0}{\rm .5}\,{\rm kcal}}}{{RT}}} \right)1/{\rm mol} \cdot {\rm sec} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{15} { } = { 10}^{8.1 \pm {0}{.3}} { exp - }\left({\frac{{{3}{.5 } \pm { 0}{.5 kcal}}}{{RT}}} \right){ 1/mol} \cdot {sec} $$\end{document}Pyrolysis of dtBP in the presence of relatively high‐pressure mixtures of CCl 4 and CCl 3 Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C 2 Cl 6 , and the HCl precursor CH 3 CCl 3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high‐pressure mixtures of CCl 3 Br and a chloromethane. Arrhenius parameters were obtained for the reactionsand the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.