UV-A photochemistry of the pesticide azinphos-methyl: generation of the highly fluorescent intermediate N-methylanthranilic acid

Azinphos-methyl (AZM) is a widely used organophosphate insecticide and acaricide, with demonstrated negative impacts on the environment. Upon absorption of UV-A radiation, this molecule undergoes photolysis to the highly fluorescent compound N-methylanthranilic acid, which undergoes subsequent photolysis to photochemically stable products. The identity of N-methylanthranilic acid as the highly fluorescent photochemical intermediate was determined by fluorescence spectroscopy, and the identity of benzazimide as the major final photoproduct was determined by 1H NMR spectroscopy and high performance liquid chromatography. A detailed UV-A photolysis mechanism is proposed, involving two pathways, the major one leading to benzazimide as the stable photoproduct, and the other to N-methylanthranilic acid as an intermediate and aniline as a final stable photoproduct. This photolysis has implications for fluorescence-based trace analysis of this pesticide, as controlled UV exposure results in significant fluorescence enhancement of AZM in solution via formation of the highly fluorescent intermediate N-methylanthranilic acid. It also has importance in the environmental fate of this pesticide, as the UV-A in sunlight is found to decompose an aqueous solution of this pesticide over the course of a single day.