Preliminary study on the fate of VX in concrete

A preliminary study has been done to examine the sorption and reaction of V X, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in an aged sample of concrete using P-31 NMR. Using "solution" NMR conditions, facile sorption of a neat liquid 15 muL droplet of VX into a 737 mg chunk of the c oncrete could be observed. The half-life for this process is about 2 min an d is attributed to VX penetrating the surface pores to form a sorbed phase tentatively assigned to a solid protonated form of VX. Little reaction occu rs during this initial sorption period; however, the sorbed VX does slowly hydrolyze with a half-life of about 3 months. During this time, the hydroly sis products of VX, ethyl methylphosphonic acid (EMPA), and diisopropylamin oethanethiol (DESH), but not VX itself, are observed to condense on the ins ide of the NMR tube around the concrete chunk. Using "solid state" MAS NMR conditions, examination of the reaction of a 5 muL VX drop with 293 mg of t he crushed concrete revealed a two-step behavior in the kinetics. An initia l reaction with a half-life of about 2 h consumes 12% of the VX. After abou t 1 h, a much slower steady-state hydrolysis ensues, exhibiting a half-life of 28 days. EMPA is the sole hydrolysis product detected in the 31P MAS NM R spectra; no toxic S-[2-(diisopropylamino)ethyl]methylphosphonothioate (EA -2192) is observed. Considering the concrete surface area, one monolayer wo uld accommodate 13% of the applied VX. Thus, the observed kinetic behavior is consistent with the concrete surface possessing a limited reactive capac ity corresponding to about one VX monolayer.