Ion-molecule reactions of O,S-Dimethyl methylphosphonothioate : Evidence for intramolecular sulfur oxidation during VX perhydrolysis

McAnoy, A. M., Williams, J., Paine, M. R. L., Rogers, M. L., & Blanksby, Stephen J. (2009) Ion-molecule reactions of O,S-Dimethyl methylphosphonothioate : Evidence for intramolecular sulfur oxidation during VX perhydrolysis. Journal of Organic Chemistry, 74(24), pp. 9319-9327.

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The alkaline perhydrolysis of the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) was investigated by studying the ion-molecule reactions of HOO(-) with O,S-dimethyl methylphosphonothioate in a modified linear ion-trap mass spectrometer. In addition to simple proton transfer, two other abundant product ions are observed at m/z 125 and 109 corresponding to the S-methyl methylphosphonothioate and methyl methylphosphonate anions, respectively. The structure of these product ions is demonstrated by a combination of collision-induced dissociation and isotope-labeling experiments that also provide evidence for their formation by nucleophilic reaction pathways, namely, (i) S(N)2 at carbon to yield the S-methyl methylphosphonothioate anion and (ii) nucleophilic addition at phosphorus affording a reactive pentavalent intermediate that readily undergoes internal sulfur oxidation and concomitant elimination of CH(3)SOH to yield the methyl methylphosphonate anion. Consistent with previous Solution phase observations of VX perhydrolysis, the toxic P-O cleavage product is not observed in this VX model system and theoretical calculations identify P-O cleavage to be energetically uncompetitive. Conversely, intramolecular sulfur oxidation is calculated to be extremely exothermic and kinetically accessible explaining its competitiveness with the facile gas phase proton transfer process. Elimination of a sulfur moiety deactivates the nerve agent VX and thus the intramolecular sulfur oxidation process reported here is also able to explain the selective perhydrolysis of the nerve agent to relatively nontoxic products.

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ID Code: 71936
Item Type: Journal Article
Refereed: Yes
Keywords: chemical warfare agents, trap mass-spectrometer, phase s(n)2 reactions, dimethyl methylphosphonate, decontamination, solvolysis, anion, stereochemistry, selectivity, reactivity
DOI: 10.1021/jo901944p
ISSN: 1520-6904 (online( 0022-3263 (print)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright © 2009 American Chemical Society
Deposited On: 25 May 2014 23:43
Last Modified: 31 May 2014 06:38

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