Meir Asscher

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

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 Ea 23 kcal mol–1, and k 2·75 × 10–5 for CuCl3– and 4·7 × 10–6 l mol–1 s–1 for CuCl42–, at 70°. Chloride ion retards the reaction progressively, until all copper(II) ion has been converted into CuCl42–. The rates are correlated with a shift in the half wave-potential of the CuI–CuII couple towards less positive values.

Redox transfer. Part VIII. Addition of benzenesulphonyl chloride and carbon tetrachloride to substituted styrenes: a kinetic study

A kinetic study of the copper chloride-catalysed addition of benzenesulphonyl chloride to a number of styrenes carrying substituents of widely different electronegativity shows that the overall rates are very little affected by the substituent. This rules out the possibility of a concerted reaction, in which the olefin should participate in the rate-determining step, and confirms a redox chain mechanism. The lack of stereospecificity of the addition of carbon tetrachloride to norbornene points to the same conclusion. β-Methylstyrene reacts much more slowly with benzenesulphonyl chloride than the other styrenes. This is attributed to an unfavourable equilibrium for sulphonyl radical addition to this olefin. Carbon tetrachloride adds at the same rate to different olefins, including β-methylstyrene, in accord with the redox chain mechanism.