Hydrolysis of prosulfuron at pH 5: evidence for a resonance-stabilized triazine cleavage product

Abstract

: 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.

Effects of the herbicides prosulfuron and metolachlor on fluxes of CO2, N2O, and CH4 in a fertilized Colorado grassland soil

“…Based on initial LC/MS analyses, three potential prosulfuron degradation products were identified that could have been present in the soil (Figure 7). These degradation products corresponded to ions of mass‐to‐charge (m/z) of 452, 425, and 254 (Figure 7) [ Bray et al , 1997; Kulowski et al , 1997]. Upon further investigation using LC/MS/MS, it was determined that the only degradation product present at detectable concentrations was the compound corresponding to m/z = 452.…”

“…The molecular structure for prosulfuron and possible structures for the three potential degradation products observed by LC/MS [ Bray et al , 1997; Kulowski et al , 1997]. …”

“…Prosulfuron (1‐(4‐methoxy‐6‐methyl‐1, 3, 5‐trazin‐2‐yl)‐3‐[2‐(3, 3, 3‐trifluoropropyl)phenylsulfonyl]urea) (Figure 1) is one of a group of sulfonylurea herbicides used widely throughout the United States and the world for control of broadleaf weeds [ Bray et al , 1997; Kulowski et al , 1997]. Metolachlor ([2‐chloro‐N‐(2‐ethyl‐6‐mehylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide]) (Figure 1) is a chloroacetanilide herbicide used for control of grassy weeds [ Stamper et al , 1997; Eykholt and Davenport , 1998; Farenhorst and Bowman , 1998].…”

Application of coupled liquid chromatography–mass spectrometry in hydrolysis studies of the herbicide ethametsulfuron-methyl

“…Sarmah and Sabadie suggested that the cleavage of the triazine ring was the most important degradation pathway for these herbicides under acidic conditions [33]. Similar degradation routes have also been proposed for prosulfuron hydrolysis in aqueous solution [38].…”

Analysis of Metsulfuron-methyl in Soil by Liquid Chromatography/Tandem Mass Spectrometry. Application to a Field Dissipation Study

“…Degradation of the triazines depends on ring cleavage of the compound, and for the triazine amines in sulfonylurea, chemical ring cleavage has been found only at or below pH 5 (Berger and Wolfe, 1996;Bray et al, 1997;Cambon and Bastide, 1997). This indicates, along with our mineralization data, that microbial degradation of the triazine part (as with the sulfonamide part) is the main mechanism of degradation of the hydrolysis products of metsulfuron-methyl.…”