Theoretical investigation on the alcoholysis reaction mechanism of nerve agents: The reaction of tabun with methanol

The alcoholysis mechanism for tabun has been systematically studied by using B3LYP/6–311++G(d,p), M06-2×/6–311++G(d,p) and MP2/6–311++G(d,p) levels. Three plausible reaction processes, the P–CN, P–N(CH₃)₂ and P–OEt disintegration pathways involving the concerted and stepwise channels are theoretically examined. To explore the effect of additional methanol and water, methanol-catalyzed and water-catalyzed alcoholysis are extensively assessed. Additionally, we also consider the effect of solvent in water by performing CPCM model at M06-2×/6–311++G(d,p) level. The results of our predictions show convincingly that the stepwise mechanism with obviously lower energy is more prominent than the concerted one and the most preferred mechanism seems to be the stepwise pathway of the P–CN cleavage channel. Moreover, our theoretical results clearly demonstrate the methanol-assisted and water-assisted alcoholysis are more easier to occur than the direct alcoholysis. Solvent effect does not have remarkable effect on the reaction mechanism. Our results certainly provide valuable information for the degradation of nerve agents.