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 ka(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 ka upon pressure. Experiments with tetrachloroethylene confirm previous values, giving k2(C2Cl4)= 0.20 × 1010 mole–1 1. sec–1 and ka(C2Cl*5)< 3 × 107 sec–1.