Alcoholysis and chemical hydrolysis of bensulfuron-methyl

Alcoholysis (methanol or ethanol) and hydrolysis (pH less than or equal to 8) of the herbicide bensulfuron-methyl at 30 or 50 degrees C involve only the breakdown of the urea part of the molecule. A high yield of the pyrimidinamine is always obtained, along with the corresponding carbamate (alcoholysis) or benzylsulfonamide (hydrolysis). The latter compound was easily cyclized (pH greater than or equal to 6). In alkaline solution, the carbomethoxy substituent of the aromatic ring was preferentially hydrolysed. In all cases, the alcoholysis and hydrolysis rates could be described well with first-order kinetics. Alcoholysis rate constants of bensulfuronmethyl and bensulfuron ranged from 0.08 to 0.15 d(-1) at 30 degrees C. Hydrolysis rate constants of bensulfuron-methyl, bensulfuron and benzylsulfonamide varied strongly with pH. The hydrolysis rate constant of bensulfuron-methyl was minimal around pH 8. The hydrolysis rate constant of bensulfuron decreased with increasing pH, whereas that of benzylsulfonamide increased with increasing pH.