Activated chloroalkyl radicals in the chlorination of trichloroethylene and other olefins

Abstract

The chlorination of mixtures of propane with trichloroethylene (chiefly), ethylene, vinyl chloride, transdichloroethylene, and tetrachloroethylene has been studied between 300 and 400°K at pressures up to 300 torr. In the chlorination of trichloroethylene, the dissociation (reaction (a)) and collisional deactivation (reaction (b)) of activated chloroalkyl radicals, formed by addition of Cl to C₂HCl₃(reaction (2)), compete on equal terms at about 50 torr total pressure. By allowing for this competition we obtain k₂(C₂HCl₃)= 3 × 10¹⁰ mole^–1 1. sec^–1. Assuming that SF₆ is completely efficient in reaction (b) we obtain k_a(C₂HCl^*₄)= 3 × 10⁸ sec^–1. Cl + A = ACl^*(A = olefin)(2) ACl^*= A + Cl (a) ACl^*+ M = ACl + M (b) Experiments with ethylene and vinyl chloride were unsuccessful because of rapid heterogeneous chlorination.

Further experiments with transdichloroethylene confirmed previous data and suggest that an anomaly observed by Knox and Riddick¹ can be explained by the dependence of k_a upon pressure. Experiments with tetrachloroethylene confirm previous values, giving k₂(C₂Cl₄)= 0.20 × 10¹⁰ mole^–1 1. sec^–1 and k_a(C₂Cl^*₅)< 3 × 10⁷ sec^–1.