Free radical substitution in aliphatic compounds. Part XXIX. Halogen atom abstraction from alkyl halides by trimethyltin radicals in the gas phase

Abstract

Mixtures of trimethyltin hydride and halogenoalkanes have been irradiated in the gas phase by a medium pressure mercury lamp. A very rapid reaction ensues in which a halogen atom in the original halogenoalkane is displaced by a hydrogen atom and trimethyltin halide is formed. The reaction is interpreted as a chain process involving halogen abstraction by trimethyltin radicals. Competitive expėriments have been carried out and in general the reaction is very unselective; the different halogens are abstracted from similar sites in the order Br > Cl > F and the reactivity of different sites lies in the order tertiary > secondary > primary. The relative rates of chlorine abstraction from a series of molecules with the formula RCCl₃ has been determined. If R is electron attracting, chlorine abstraction is facilitated and if R is electron repelling chlorine abstraction is retarded. These results are considered to be evidence of a polar effect exactly opposite to that observed in reactions involving hydrogen abstraction by chlorine atoms.