Flazasulfuron: alcoholysis, chemical hydrolysis, and degradation on various minerals

The herbicide flazasulfuron undergoes rapid alcoholysis. High yields of the corresponding carbamate and aminopyrimidine are obtained after the alcoholysis process (methanol or ethanol) at 30 degrees C, in the course of which the concomitant rearrangement reaction remains minor. Hydrolysis (pH ranging from 5 to 11) of flazasulfuron at 30 degrees C principally involves the rearrangement into urea after elimination of SO(2) and can lead, in a small proportion, to both aminopyrimidine and pyridinesulfonamide. First-order kinetics correctly describes the rates of alcoholysis and hydrolysis. The sulfonylurea-bridge contraction and final transformation into the correspondent amine were evaluated with a first-order kinetics hypothesis. Transformations in amine and urea in aqueous medium are pH dependent. The chemical degradation of flazasulfuron on various dry minerals (calcium bentonite, kaolinite, silica, montmorillonite, and alumina) was investigated at 30 degrees C. The rearrangement reaction is the only one observed in the presence of kaolinite and alumina. However, hydrolysis and rearrangement have the same reaction rate in the presence of silica. The hydrolysis paths of flazasulfuron are comparable to the ones described for rimsulfuron.