Ab Initio Molecular Orbital and Density Functional Studies on the Solvolysis of Sarin and O,S-Dimethyl Methylphosphonothiolate,a VX-like Compound

摘要

Potential energy surfaces for the alkaline hydrolysis of sarin and O,S-dimethyl methylphospho-nothiolate,a VX model compound,and the perhydrolysis of the latter have been computed at the MP2/6-31+G(d)//mPW1K/MIDI! level of theory.The effect of aqueous solvation was accounted for via the integral equation formalism polarizable continuum model(IEF-PCM)at the HF/6-31+G(d)level.Excellent agreement with the experimental enthalpy of activation for alkaline hydrolysis of sarin was found.For the alkaline hydrolysis of O,S-dimethyl methylphosphonothiolate,it was found that the P-O and P-S bond cleavage processes are kinetically competitive but that the products of P-S bond cleavage are thermodynamically favored.For the perhydrolysis of O,S-dimethyl methylphosphonothiolate,it was found that P-O bond cleavage is not kinetically competitive with P-S bond cleavage.In both cases,the data support initial formation of trigonal bipyramidal intermediates and demonstrate kinetic selectivity for nucleophilic attack on the face opposite the more apicophilic methoxide ligand.