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: Prosulfuron is a herbicide for the selective control of broadleaf weeds in corn. In order to examine the e †ect of pH on the stability of prosulfuron in aqueous solution, a hydrolysis experiment was conducted in bu †er at pH 5, 7 and 9 utilizing [phenyl-14C] and [triazine-14C]prosulfuron. Prosulfuron was found to be stable under neutral and basic conditions and hydrolytically unstable under acidic conditions days). One of the major routes of deg-(T " D10 radation at pH 5 involved hydrolysis of the sulfonylurea bridge to yield the corresponding phenyl-and triazine-cleavage products and minor amounts of desmethyl-prosulfuron and dihydroxymethyltriazine. In addition to these hydrolysis products, an unknown species was observed at signiÐcant levels after 30 days (D20% of the applied dose). A large-scale experiment was subsequently performed to generate additional material for the spectroscopic characterization and identiÐcation of this unknown degradate. A thorough spectral evaluation of this unknown revealed a resonance-stabilized derivative of the parent molecule which stemmed from a hydrolytic opening of the triazine ring of desmethylprosulfuron. Although this triazine ring-opening phenomenon was Ðrst described for chlorsulfuron, a structurally related sulfonylurea herbicide, the structure of the product was only postulated. Recently, Cambon et al. described the hydrolysis kinetics of thifensulfuron and thifensulfuron-methyl which resulted in cleavage of the sulfonylurea bridge and triazine ring-opening. Our results support these Ðndings and we herein describe the characterization and identiÐcation of this resonance-stabilized species by comparison with the recently synthesized authentic reference standard.

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