Photodecomposition of chlorothalonil in benzene

Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) in benzene was photodecomposed by sunlight or low energy ultraviolet irradiation to a monophenyl adduct identified as 3,5,6-trichlorobiphenyl-2,4-dicarbonitrile. However, irradiation with a 100-W high-energy ultraviolet lamp yielded an additional compound identified as 2′, 5′ -dichloro-m-terphenyl-4′, 6′-dicarbonitrile. Photolysis was followed by a steady decrease in the chlorothalonil and monophenyl adduct concentrations, with a concomitant increase in the diphenyl adduct.