Some reactions of alkyl radicals

Abstract

The first part of the Thesis describes the work carried out in a study of the thermal decomposition of n-propyl and n-fluoropropyl radicals. n-Propyl radicals were generated by the high temperature chlorination of propane. The chlorine atoms produced in this reaction can abstract a hydrogen atom from the primary position in the propane. The n-propyl radical thus formed can either react with molecular chlorine present in the system or, at the temperature used, decompose to form ethylene and a methyl radical. Approximate values for the rate parameters of this reaction were obtained. A competitive technique for obtaining the rate parameters for the thermal decomposition of n-fluoropropyl radicals relative to the decomposition of the n-propyl radical was developed. Unfortunately due to the rapid decomposition of the starting material: 2,2-difluoropropane it was not possible to carry out these experiments. During the course of this study kinetic data was obtained from the photolytic chlorination of propane, the thermal decomposition of n-propyl chloride and sec-propyl chloride and the competitive photolytic chlorination of propane and 2,2-difluoropropane. The second part of the thesis describes a study of the comparison of the gas phase hydrogen abstraction reactions of trifluoromethyl and methyl radicals in the gas phase with n-butane, n-butyl fluoride and 1,1,1-trifluoropentane. Trifluoromethyl radicals were generated by the photolysis of trifluoromethyl iodide. The relative selectivities of the radicals were obtained by the quantitative measurement of the iodides formed from the reaction of the alkyl radicals with trifluoromethyl iodide. Methyl radicals were generated by the photolysis of azomethane. The radicals thus formed abstracted hydrogen atoms from one of the four reaction sites within the substituted butanes. The reactions were carried out in the presence of methyl iodide which acted as a chain propagator, the alkyl radicals formed abstracting iodine from the methyl iodide. The quantitative measurement of the alkyl iodides thus formed enabled the relative selectivities of the methyl radicals to be established. The results obtained showed the effect of the substituents on the relative selectivities of the two radicals for the different reaction sites within the alkanes.