Room-temperature reactions of VX, GB, GD, and HD with nanosize Al(2)O(3) (AP-Al(2)O(3)) have been characterized by (31)P, (13)C, and (27)Al MAS NMR. Nerve agents VX, GB, and GD hydrolyze to yield surface-bound complexes of their corresponding nontoxic phosphonates. At sufficiently high loadings, discreet aluminophosphonate complexes, Al[OP(O)(CH(3))OR](3), are generated which are identical to synthesized model compounds. Thus the reaction with phosphonic acids is not just surface-limited, but can continue to the core of alumina particles. HD mainly hydrolyzes at lower loadings to yield thiodiglycol (TG, 71%) and a minor amount of the CH-TG sulfonium ion (12%), although some elimination of HCl is also observed (17%). The reactive capacity for HD is evidently exceeded at high loadings, where complete conversion to TG is hindered. However, addition of excess water results in the quantitative hydrolysis of sorbed HD to CH-TG. On AP-Al(2)O(3) dried to remove physisorbed water, (13)C CP-MAS NMR detects a surface alkoxide consistent with that of TG.
Both V-type nerve agents MeP(O)(OR)(SCH2CH2NR‘2), VX (R = C2H5; R‘ = i-C3H7) and its isomeric analog RVX (the “Russian V-agent”, R = i-C4H9; R‘ = C2H5), react slowly but completely with an equimolar amount of H2O via exclusive P−S cleavage to produce the corresponding phosphonic acid (MeP(O)(OR)OH) and 2-aminoethanethiol (HSCH2CH2NR‘2). The reaction is believed to be initiated by nucleophilic attack of the deprotonated phosphonic acid on the protonated V-agent to produce a diphosphonate intermediate ((MeP(O)(OR))2O) that rapidly hydrolyzes to regenerate the phosphonic acid. The autocatalytic ionic chain reaction is thus continued in the nearly nonaqueous reaction medium. The viscous final product mixture remains reactive toward freshly added trace amounts of the V-agent, giving the same final reaction half-life of 13−15 h at 23 °C. When water is insufficient and depleted, the diphosphonate intermediate accumulates and reacts with the aminoethanethiol to regenerate the V-agent. This autocatalytic hydrolysis process is not observed with a simpler phosphonothioate analog (MeP(O)(OC2H5)(SC2H5)), which suggests that the attack of the phosphonic acid on the V-agent is intramolecularly assisted by the protonated amino group.
Environmentally friendly and noncorrosive methods to decontaminate the blister agent mustard (HD) bis(2-chloroethyl) sulfide are currently being developed. HD may be rendered nonvesicant by oxidation to the corresponding sulfoxide. In microemulsions, the mildly basic molybdate/peroxide oxidant system rapidly oxidizes HD initially to the sulfoxide. Secondary oxidation to the sulfone does occur, but this reaction is about 2 orders of magnitude slower. A microemulsion found to be stable at low temperature was identified, enabling the decontamination of HD at -30 °C. The mild basicity of such solutions also affords the peroxyhydrolysis (OOH -) of nerve agents GD and VX.
A preliminary study has been done to examine the sorption and reaction of VX, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in an aged sample of concrete using 31P NMR. Using “solution” NMR conditions, facile sorption of a neat liquid 15 μL droplet of VX into a 737 mg chunk of the concrete could be observed. The half-life for this process is about 2 min and is attributed to VX penetrating the surface pores to form a sorbed phase tentatively assigned to a solid protonated form of VX. Little reaction occurs during this initial sorption period; however, the sorbed VX does slowly hydrolyze with a half-life of about 3 months. During this time, the hydrolysis products of VX, ethyl methylphosphonic acid (EMPA), and diisopropylaminoethanethiol (DESH), but not VX itself, are observed to condense on the inside of the NMR tube around the concrete chunk. Using “solid state” MAS NMR conditions, examination of the reaction of a 5 μL VX drop with 293 mg of the crushed concrete revealed a two-step behavior in the kinetics. An initial reaction with a half-life of about 2 h consumes 12% of the VX. After about 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 NMR spectra; no toxic S-[2-(diisopropylamino)ethyl]methylphosphonothioate (EA-2192) is observed. Considering the concrete surface area, one monolayer would accommodate 13% of the applied VX. Thus, the observed kinetic behavior is consistent with the concrete surface possessing a limited reactive capacity corresponding to about one VX monolayer.
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