HYDROLYSIS KINETICS OF THIFENSULFURON METHYL IN AQUEOUS BUFFER SOLUTIONS

The hydrolysis of thifensulfuron methyl and thifensulfuron were invest igated 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 thif ensulfuron, hydrolysis rates were of the same order of magnitude as th ifensulfuron methyl at acidic pH, but very low at alkaline pH. In acid ic solutions, cleavage of the sulfonylurea bridge and O-demethylation of the methoxy group of the triazine ring occurred concurrently The re sulting intermediates gave two parallel reactions: cleavage of the sul fonylurea bridge and opening of the triazine ring. The relative rates of the different hydrolysis pathways were influenced by the pK(a) of c ompounds. At alkaline pH, thifensulfuron methyl hydrolyzed to thifensu lfuron, which was slowly transformed by cleavage of the sulfonylurea b ridge and O-demethylation.