Photolysis and hydrolysis of rimsulfuron

The degradation in the liquid phase of rimsulfuron and its commercial 250 g kg(-1) WG formulation (Titus(R)) was investigated. Photolysis reactions we re carried out at 25 degrees C by a high-pressure mercury are (Hg-UV) and a solar simulator (Suntest), while the hydrolysis rate was determined by kee ping aqueous buffered samples in the dark. The effects of solvent and water pH on reaction kinetics were studied, and the results compared to literatu re data. Photoreactions of the commercial product in organic solvents were faster than pure rimsulfuron. Under simulated sunlight in water, the half-l ife for the photolysis reaction ranged from one to nine days at pH 5 and 9, respectively. The hydrolysis rate was as high as the photolysis rate, but decreased on increasing water pH. The main metabolite identified in neutral and alkaline conditions as well as in acetonitrile was N-[(3-ethylsulfonyl )-2-pyridinyl]-4,6-dimethoxy-2-pyridinamine, while N-(4,6-dimethoxy-2-pyrim idinyl)-N-[(3-(ethylsulfonyl)-2-pyridinyl)]urea and minor metabolites preva iled in acidic conditions. (C) 1999 Society of Chemical Industry.