LASER FLASH-PHOTOLYSIS STUDIES OF AROYL XANTHATES AND CARBOXYLIC DITHIOCARBAMIC ANHYDRIDES

Results of a photochemical study based on nanosecond laser flash photolysis of some representative aroyl xanthates and carboxylic dithio carbamic anhydrides (1b, 9a - 9d) are presented. The 266 nm or 308 nm laser pulse excitation of the substrates in acetonitrile produces radical intermediates, arising through C(O)S and C(S)S bond fissions. These intermediates are characterized by their lifetimes, second-order decays and facile quenching by free radical quenchers such as 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl (HTEMPO) and di-tert-butylnitroxyl (DTBN) (kq = (0.1 - 6) × 109 M-1 s-1). Xanthone triplet is quenched by the substrates at diffusion-controlled rates (k = (1.4 - 4.8) × 1010 M-1 s-1), and results in the same transient radical intermediates as those observed on direct photolysis. © 1990.