Evaporation and Degradation of VX on Silica Sand

The evaporation and degradation of VX (O-ethyl S-[2-N,N-(diisopropylamino)ethyl] methylphosphonothioate) on silica sand and borosilicate glass were measured using vapor analysis and IT solid state magic angle spinning nuclear magnetic resonance (SSMAS NMR) spectroscopy. IT SSMAS NMR studies of VX degradation on crushed glass, air-dried sand, and oven-dried sand at a variety of temperatures showed that the final product was nontoxic ethyl methylphosphonic acid (EMPA), produced via the toxic diethyl dimethylpyrophosphonate intermediate. The reaction exhibited a lag time that depended upon the quantity of water and EMPA that were present in the initial sample of VX and was autocatalytic; EMPA was both the catalyst and product for the degradation of VX. P-31 SSMAS NMR studies of VX on moist sand at a variety of temperatures showed that the final product was nontoxic EMPA; observed intermediates were protonated VX, O-ethyl methylphosphonothioic acid, and toxic EA-2192 (S-[2-NN-(diisopropylamino)ethyl methylphosphonothioic acid). The VX degradation mechanism differed on the moist and dry surfaces; the activation energies were 80 kJ/mol on moist sand and similar to 46 kJ/mol on glass, air-dried, and oven-dried sand. The VX degradation rate was 5 to 9 times slower on moist sand than on air-dried sand. Analysis of the vapor emitted showed that the maximum vapor concentration coincided with the maximum surface area of the droplets, which was at similar to 300 min. After four days, no further change in the concentration of vapor emitted was detected; approximately 9% of the incident VX drop on sand and similar to 60% of the incident VX drop on glass had been recovered as VX vapor.