Behavior of four sulfonylurea herbicides in the presence of hydroxy compounds.

The behavior of four sulfonylurea herbicides (metsulfuron methyl, chlorsulfuron, chlorimuron ethyl, and bensulfuron methyl) was studied in the presence of various hydroxy compounds. When dissolved at 30 degrees C in simple primary, secondary, or tertiary alcohols (methanol, ethanol, isopropyl alcohol, and tert-butyl alcohol) and in glycerol or in poly(ethylene glycol), most of these herbicides underwent rapid alcoholysis involving the breakdown of the urea part of the molecule. The corresponding sulfonyl carbamate is recovered in high yields, along with a small amount of sulfonylamide formed in the concomitant hydrolysis. Degradation rate constants and the selectivity of conversion were established. The addition of buffered water (pH 7.0) inhibited the alcoholysis reaction, leaving only hydrolysis, as already observed with concentrated saccharide solutions. In phenol solution, slight herbicide hydrolysis was primarily observed. It appeared that alcoholysis reactions only occurred under very particular conditions when sulfonylurea herbicides are dissolved in pure alcohols, without buffered water. These results led to the conclusion that in soil, similar alcoholysis reactions seem unlikely.