The behaviour of 1,1,2,2-tetrachloroethane and trichloroethene in chlorination reactions where the supply of chlorine is varied, either by change in chlorocarbon: Cl-2 feed ratio or the quantity of supported copper(II) chloride catalyst or by the use of an anhydrous hydrogen chloride/dioxygen feed as the source of chlorine, i.e. oxychlorination conditions, is described. Depending on the exact conditions used, the products are trichloroethene, pentachloroethane or tetrachloroethene. The products and the conditions under which they are observed are both in harmony with a previously proposed reaction scheme in which there is interplay between heterogeneous and homogeneous reactions. It is possible to define sets of reaction conditions which lead to improvements in selectivity towards the formation of either CHCl=CCl2 or CCl2=CCl2 without significant formation of oligomeric species. (C) 2013 Elsevier B.V. All rights reserved.