Phototransformation of carbaryl in aqueous solution - Laser-flash photolysis and steady-state studies

Aqueous carbaryl is shown to be photolysed with a low quantum yield ((2.1 +/- 0.2) x 10(-3) in air-saturated medium) into 1,2-naphthoquinone, 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone and 7-hydroxy-1,4-naphthoquinone. In acetonitrile and methanol, carbaryl is mostly photoconverted into 1-naphthol. This behaviour contrasts with those of carbamates and aryl esters that generally undergo efficient photo-Fries rearrangement. Several transient species were detected by laser-flash photolysis in water: the triplet-triplet (T-T) absorption (lambda(max) = 410 nm, k(d) = 3.5 x 10(5) s(-1)), the solvated electrons (phi = 0.022 +/- 0.002), the naphthoxyl radicals and a long-lived unassigned species. The mechanism of phototransformation is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.