Hydrolysis kinetics of thifensulfuron methyl in aqueous buffer solutions

The hydrolysis of thifensulfuron methyl and thifensulfuron were investigated in buffered aqueous solutions with pH values of 4, 5, 9, and 10. Hydrolysis of thifensulfuron methyl was pH dependent and relatively fast both in acidic and alkaline buffer solutions. In the case of thifensulfuron, hydrolysis rates were of the same order of magnitude as thifensulfuron methyl at acidic pH, but very low at alkaline pH. In acidic solutions, cleavage of the sulfonylurea bridge and O-demethylation of the methoxy group of the triazine ring occurred concurrently The resulting intermediates gave two parallel reactions: cleavage of the sulfonylurea bridge and opening of the triazine ring. The relative rates of the different hydrolysis pathways were influenced by the pK(a) of compounds. At alkaline pH, thifensulfuron methyl hydrolyzed to thifensulfuron, which was slowly transformed by cleavage of the sulfonylurea bridge and O-demethylation.