Role of the P鈥揊 Bond in Fluoride-Promoted Aqueous VX Hydrolysis: An Experimental and Theoretical Study

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• 作者：Daniele Marciano ; Ishay Columbus ; Shlomi Elias ; Michael Goldvaser ; Ofir Shoshanim ; Nissan Ashkenazi ; Yossi Zafrani
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：November 16, 2012
• 年：2012
• 卷：77
• 期：22
• 页码：10042-10049
• 全文大小：385K
• 年卷期：v.77,no.22(November 16, 2012)
• ISSN：1520-6904

文摘

Following our ongoing studies on the reactivity of the fluoride ion toward organophosphorus compounds, we established that the extremely toxic and environmentally persistent chemical warfare agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) is exclusively and rapidly degraded to the nontoxic product EMPA (ethyl methylphosphonic acid) even in dilute aqueous solutions of fluoride. The unique role of the P鈥揊 bond formation in the reaction mechanism was explored using both experimental and computational mechanistic studies. In most cases, the 鈥淕-analogue鈥?(O-ethyl methylphosphonofluoridate, Et-G) was observed as an intermediate. Noteworthy and of practical importance is the fact that the toxic side product desethyl-VX, which is formed in substantial quantities during the slow degradation of VX in unbuffered water, is completely avoided in the presence of fluoride. A computational study on a VX-model, O,S-diethyl methylphosphonothioate (1), clarifies the distinctive tendency of aqueous fluoride ions to react with such organophosphorus compounds. The facility of the degradation process even in dilute fluoride solutions is due to the increased reactivity of fluoride, which is caused by the significant low activation barrier for the P鈥揊 bond formation. In addition, the unique nucleophilicity of fluoride versus hydroxide toward VX, in contrast to their relative basicity, is discussed. Although the reaction outcomes were similar, much slower reaction rates were observed experimentally for the VX-model (1) in comparison to VX.