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

Abstract

Aqueous carbaryl is shown to be photolysed with a low quantum yield ((2.1±0.2)×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 ( λ max=410 nm, k d=3.5×10 5 s −1), the solvated electrons ( φ=0.022±0.002), the naphthoxyl radicals and a long-lived unassigned species. The mechanism of phototransformation is discussed.