Addition of a chlorine atom to tetrachloroethylene

The gas-phase competitive photochlorination Cl2 + C 2Cl4 + 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 Cl 2 + 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 Cl + C2Cl4 → 2C2Cl5 k2 and C2Cl 5 → 4C2Cl4 + Cl, k4 where C2Cl5 is a thermalized radical. These results, combined with known thermochemical data, yield: D(C2Cl 4-Cl) = 16.9, D(C2Cl5-H) = 95.8 and D(C 2Cl5-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 C 2H4, 1,2-C2H2Cl2, C 2HCl3 and C2Cl4 are discussed.SCOPUS: ar.j