DFT study on the hydrolysis of metsulfuron-methyl: A sulfonylurea herbicide

Sulfonylureas are an important group of herbicides widely used for a range of weeds and grasses control particularly in cereals. However, some of them tend to persist for years in environments. Hydrolysis is the primary pathway for their degradation. To understand the hydrolysis behavior of sulfonylurea herbicides, the hydrolysis mechanism of metsulfuron-methyl, a typical sulfonylurea, was investigated using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level. The hydrolysis of metsulfuron-methyl resembles nucleophilic substitution by a water molecule attacking the carbonyl group from aryl side (pathway a) or from heterocycle side (pathway b). In the direct hydrolysis, the carbonyl group is directly attacked by one water molecule to form benzene sulfonamide or heterocyclic amine; the free energy barrier is about 52-58 kcal mol(-1). In the autocatalytic hydrolysis, with the second water molecule acting as a catalyst, the free energy barrier, which is about 43-45 kcal mol(-1), is remarkably reduced by about 11 kcal mol(-1). It is obvious that water molecules play a significant catalytic role during the hydrolysis of sulfonylureas.