Comparison of the hydrolytic stability of S-(N,N-diethylaminoethyl) isobutyl methylphosphonothiolate with VX in dilute solution

The stability of S-(N,N-diethylaminoethyl) isobutyl methylphosphonothiolate - a V-type nerve agent developed by the former Soviet Union - in the environment is an important parameter in threat assessment analysis and for the determination of use, production, testing and storage of this chemical warfare agent. S-(N,N-Diethylaminoethyl) isobutyl methylphosphonothiolate is a structural isomer of the nerve agent VX developed by the USA and the UK and will be referred to as VXA (VX analog) in this presentation. Because VXA and VX differ structurally, even though they do have the same molecular formula, it is expected that their physical and chemical properties would be different. This preliminary investigation was undertaken to determine the relative hydrolysis rate of VXA compared with VX. The hydrolysis of each compound at approximately 1 mg ml-1 in unbuffered water at pH 7 was determined side-by-side. The half-lives for VXA and VX were determined to be 12.4 days and 4.78 days, respectively. Agent VXA hydrolyzed 2.6 times more slowly than VX, and each agent followed second-order hydrolysis kinetics. These results imply that VXA is more persistent in the environment and therefore poses a greater threat. These results also imply that VXA is more likely to be detected, if present, during an inspection in support of the Chemical Weapons Convention.