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

The oxygen-inhibited photochlorination and the chlorine-photosensitized oxidation of tetrachloroethylene 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[Cl 2]/dt = k 1I a 1/2[Cl 2]/(k 1 2/k 0 2+[O 2]) 1/2 and that of oxidation by -(d[C 2Cl 4] or d[C 2HCl 5]/dt-d[Cl 2]/dt = I a[0 2](k+k'[O 2]), k and k' for C 2HCl 5 being about 35 % higher than for C 2Cl 4. The maximum quantum yield of oxidation is about 300. These results are explained by a mechanism involving the bimolecular radical chain propagating step 2C 2Cl 5O 2 →2C 2Cl 5O+O 2. Rate constants have been estimated.SCOPUS: ar.j