Redox transfer. Part IX. Chlorination of olefins by copper(II) chloride

Abstract

Evidence for a homolytic interaction between copper(II) chloride and olefins is obtained from the products of the thermal reaction with cyclohexene and with but-2-ene. The initially formed chlorobutyl radical reacts with further copper(II) chloride to give 2,3-dichlorobutane in a completely non-stereospecific fashion. The feasibility of this kind of radical generation is discussed. Styrene gives 1,2-dichloroethylbenzene in a reaction which is first order in both reactants, with E_a 23 kcal mol^–1, and k 2·75 × 10^–5 for CuCl₃^– and 4·7 × 10^–6 l mol^–1 s^–1 for CuCl₄^2–, at 70°. Chloride ion retards the reaction progressively, until all copper(II) ion has been converted into CuCl₄^2–. The rates are correlated with a shift in the half wave-potential of the Cu^I–Cu^II couple towards less positive values.