Gas-phase chlorine-photosensitized oxidation and oxygen-inhibited photochlorination of tetrachloroethylene and pentachloroethane

Abstract

The oxygen-inhibited photochlorination and the chlorine-phostosensitized oxidation of tetra-chloroethylene and pentachloroethane have been studied in the gas phase at 353·5 and 373·4°K. The rate of chlorination of both compounds is given by –d{Cl₂}/dt=k₁I^½_a{Cl₂}/(k²₁/k²₀+{O₂})^½ and that of oxidation by –d[C₂Cl₄] or d[C₂HCl₅]/dt– d[Cl₂/dt]=I_a[O₂]/(k+k′[O₂]), k and k′ for C₂HCl₅ being about 35 % higher than for C₂Cl₄. The maximum quantum yield of oxidation is about 300. These results are explained by a mechanism involving the bimolecular radical chain propagating step 2C₂Cl₅O₂→ 2C₂Cl₅O+O₂. Rate constants have been estimated.