Addition of a chlorine atom to tetrachloroethylene

Abstract

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 k_a 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.