Addition of a chlorine atom to tetrachloroethylene

The gas-phase competitive photochlorination Cl2+ C2Cl4+ 1,2-C2H4Cl2 has been studied at 310°K between 40 and 642 torr in the presence and absence of added CO2 and SF6. The results are explained in terms of a mechanism in which the activated C2Cl*5 radical initially formed by addition of a Cl atom to C2Cl4 is deactivated by collision much more rapidly than it can react. The experimental data, combined with those from a parallel study of the competition Cl2+ C2Cl4+ C2H6 at 348°K and those from previous studies at higher temperatures, lead to the new values log10k2(mole–1 l. sec–1)= 10.1 and log10k4(sec–1)= 13.51 – 16080/4.576T. for the reactions [graphic omitted] and [graphic omitted] where C2Cl5 is a thermalized radical. These results, combined with known thermochemical data, yield: D(C2Cl4—Cl)= 16.9, D(C2Cl5—H)= 95.8 and D(C2Cl5—Cl)= 72.6 kcal mole–1, ΔH°f,298(C2Cl5)= 8.4 kcal mole–1 and S°298(C2Cl5)= 96.4 cal mole–1 deg.–1. The rate constant ka for the reaction C2Cl*5→ C2Cl4+ Cl is estimated to be less than 4 × 107 sec–1. Existing data on addition-substitution competitive photochlorinations of C2H4, 1,2-C2H2Cl2, C2HCl3 and C2Cl4 are discussed.