Hydrolytic degradation of azimsulfuron, a sulfonylurea herbicide

The chemical degradation of the herbicide azimsulfuron was investigated in aqueous solutions at different pH values. The hydrolysis rate, determined by HPLC analyses, was pH dependent and was much faster in acidic than in neutral or weakly basic conditions. The metabolites formed at different pH values were compared with standards when possible or isolated and identified using ESI-LC-MS/MS, 1H NMR and 13C NMR. The two main products of hydrolysis in mild acidic solution were identified as 2-amino-4,6-dimethoxy-pyrimidine and 2-methyl-4-(2-methyl-2H-tetrazol-5-yl)-2H-pyrazole-3-sulfonamide, both produced as a result of the sulfonylurea bridge cleavage. Under basic conditions, a new product, a substituted 2-pyrimidinamine, deriving from the contraction of the sulfonylurea bridge, was isolated and completely characterized for the first time.