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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.

The syntheses of four hydrolysis products isolated from environmental studies on the title compound are reported. Spectral comparison of these synthetic standards with study isolates provided proof for sulfonyl urea intact triazine ring hydrolysis.

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