Photolysis of bromotrichloromethane in the presence of dichloromethane, difluoromethane, chlorofluoromethane and dichlorofluoromethane

Abstract

The photolysis of bromotrichloromethane using light of λ= 365 mµ, in the presence of CH₂Cl₂, CH₂FCl, CF₂H₂ and CHFCl₂ has been investigated. The primary process (1) was found to be temperature dependent with an apparent activation CCl₃Br +hv→ CCl₃·+ Br·(1) energy of 6 330 ± 300 cal mol^–1, in good agreement with earlier work.¹ The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the halomethane and the only chain termination products are hexachlorethane and molecular bromine. Nonetheless the reaction do not show the expected light dependancy and also show a partial order in the halomethane. Four complicating factors are shown to be important; reversibility of the hydrogen abstraction by trichloromethyl radicals, reversibility of the initiation step, hydrogen abstraction by bromine atoms leading to an alternative chain mechanism and termination involving the halomethyl radicals. Notwithstanding these complications reasonable estimates of the Arrhenius parameters for reaction (2), the hydrogen abstraction by trichloromethyl radicals can be made. CCl₃·+ RH → CCl₃H + R·(2)[graphic omitted]