Divalent Metal Ion-Catalyzed Hydrolysis of Phosphorothionate Ester Pesticides and Their Corresponding Oxonates
作者:Jean M. Smolen、Alan T. Stone
DOI:10.1021/es960499q
日期:1997.6.1
The divalent metal ion-catalyzed hydrolysis of thionate (P=S) and oxonate (P=O) organophosphorus pesticides has been examined in light of three possible catalysis mechanisms: (1) metal ion coordination of the thionate sulfur or oxonate oxygen to enhance the electrophilicity of the phosphorus electrophilic site; (2) metal ion coordination and induced deprotonation of water to create a reactive nucleophile; and (3) metal ion coordination of the leaving group to facilitate its exit. The effect of the following metals at a concentration of 1 mM was examined: COII, Ni-II, Cu-II, Zn-II and Pb-II. These metal ions were chosen for their ability to complex organic ligands and inorganic nucleophiles. Of these metal ions, Cu-II possesses properties most suitable for all three catalytic mechanisms and serves as the most effective catalyst for the five thionate esters (chlorpyrifos-methyl, zinophos, diazinon, parathion-methyi, and ronnel) and the two oxonate esters (chlorpyrifos-methyl oxon and paraoxon) included in this study. A decrease in the degree of Cu-II catalysis at high pH arises from solubility limitations. Pb-II nearly matches Cu-II as a catalyst for oxonate esters, but is a less effective catalyst for thionate esters. Catalysis by Co-II, Ni-II, and Zn-II is negligible. Phenolate product analysis indicates that metal catalysis in some instances shifts hydrolysis from alkyl carbon-centered pathways to phosphorus-centered pathways.