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 (<F>(2.1±0.2)×10−3</F> 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 (<F>λmax=410</F> nm, <F>kd=3.5×105</F> s−1), the solvated electrons (<F>φ=0.022±0.002</F>), the naphthoxyl radicals and a long-lived unassigned species. The mechanism of phototransformation is discussed. [Copyright &y& Elsevier]