18429-96-4Relevant academic research and scientific papers
Divalent metal ion-catalyzed hydrolysis of phosphorothionate ester pesticides and their corresponding oxonates
Smolen, Jean M.,Stone, Alan T.
, p. 1664 - 1673 (1997)
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: Co(II), 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-methyl, 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.
