The influence of dissolved metal ions and metal-containing surfaces on the hydrolysis of phosphoro(thio)nate ester pesticides.

摘要

Hydrolysis is an important degradation pathway of organophosphorus ester pesticides. Three mechanisms are believed to be responsible for metal-catalyzed hydrolysis: (1) coordination of the ester by the metal catalyst to activate the molecule towards nucleophilic attack; (2) deprotonation of water by the metal catalyst to create a metal-hydroxo nucleophile; (3) coordination of the leaving group by the metal catalyst to enhance its leaving ability. The objective of this research is to evaluate how ester structure, metal ion properties, and pH affect metal-catalyzed hydrolysis.;In the presence of Cu;Previous investigations of the metal-catalyzed hydrolysis of chlorpyrifos methyl have indicated that chelate formation between the metal catalyst, the thionate sulfur, and the ring nitrogen atom of the ester catalyze the hydrolysis reaction. This may not be the case for two reasons: (1) the metal-catalyzed hydrolysis of parathion methyl, paraoxon, and ronnel (esters that do not contain ring nitrogen atoms) has been observed; (2) the basicity of the ring nitrogen atom of chlorpyrifos may be too low for effective metal coordination.;Hydrolysis of chlorpyrifos methyl produces alcoholate and phenolate leaving groups. In metal-free solution, the amount of phenolate product formed does not equal the amount of parent ester lost from solution. Metal ions and metal oxide surfaces catalyze hydrolysis reactions in such a way that there is more phenolate product formed relative to the amount of parent compound hydrolyzed. Similar results were observed with the other esters examined.;The thionate (P = S) and oxonate (P = O) esters of chlorpyrifos methyl exhibit different hydrolysis behavior. The oxonate ester hydrolyzes faster than thionate ester in metal-free solution. However, the thionate ester is more susceptible than the oxonate ester to hydrolysis catalyzed by C