Laser flash photolysis studies of aroyl xanthates and carboxylic dithiocarbamic anhydrides

Abstract

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) (k_q = (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.