Direct photolyses of thiobencarb and ethiofencarb in aqueous phase

The direct photolyses of thiobencarb and ethiofencarb in water were investi gated by product studies and laser flash photolysis. At 253.7 nm and in air -saturated solution, thiobencarb is photoconverted into 4-chlorobenzaldehyd e and 4-chlorobenzylalcohol with a good efficiency (phi = 0.14 +/- 0.02). E thiofencarb is phototransformed with a close efficiency (phi = 0.12 +/- 0.0 2) into sulfoxide, 2-methylphenyl-methylcarbamate and two unidentified oxid ation products. The homolytic cleavage of the CS bonds takes place as prove d by the detection of benzylic-type radicals by transient absorption spectr oscopy. With thiobencarb, this reaction yields finally 4-chlorobenzaldehyde . On the other hand, 4-chlorobenzylalcohol and 2-methylphenyl-methylcarbama te are likely to arise from the heterolytic cleavage of the CS bonds. The s ulfoxide formation observed in the case of ethiofencarb may result from an electron transfer from the triplet excited state to oxygen and involve a pe roxysulfoxide as intermediate. (C) 2000 Elsevier Science S.A. All rights re served.