Photosensitized dechlorination of polychlorinated benzenes. 1. Carbazole-photosensitized dechlorination of hexachlorobenzene

Photosensitized dechlorination of hexachlorobenzene (HCBz) in hexane and in acetonitrile (MeCN) solutions as well as in aqueous solutions of poly(sodium styrenesulfonate-co-N-vinylcarbazole) (PSSS-VCz) copolymer has been studied. It was found that the reaction was photosensitized by both molecular and polymeric carbazole (Cz) chromophores. The products have been identified using GC, NMR and MS analyses. The detected products were: pentachlorobenzene, tetrachlorobenzenes, trichlorobenzenes, dichlorobenzenes, chlorobenzene and benzene. It was postulated that dechlorination process is mediated by an electron transfer from the excited carbazole chromophores to the molecule of chlorinated benzene with subsequent heterolytic cleavage of the C---Cl bond. The photosensitized by Cz dechlorination process is a stepwise reaction. The rate of photosensitized degradation of HCBz in aqueous PSSS-VCz solution was considerably higher than in organic solvents.