Autocatalytic Hydrolysis of V-Type Nerve Agents

Abstract

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.

Electrochemical properties of surface-confined films of single-walled carbon nanotubes functionalised with cobalt(II)tetra-aminophthalocyanine: Electrocatalysis of sulfhydryl degradation products of V-type nerve agents

“…Maximum catalytic currents were observed at equal or greater than pH 9.0 for both analytes. This behaviour is consistent with the pK a of DEAET reported as 8.3 at 25 °C [47]. Thus, all subsequent studies here for DMAET, DEAET were performed at pH 9.3 PBS with some works at physiological pH 7.4 conditions.…”

Toward antibody-catalyzed hydrolysis of organophosphorus poisons

“…For instance, the phosphate buffer was shown to enhance hydrolysis up to 10-fold as compared with hydrolysis in the Tris⅐HCl buffer at the same pH, concentration, and temperature. This confirms the hypothesis of a phosphonate-based mechanism for the autocatalytic hydrolysis of VX in the presence of stoichiometric or substoichiometric amounts of water, as claimed by Y. C. Yang (34). To overcome this hydrolysis mechanism, thiophosphonate hydrolysis was performed in 0.1 M Tris⅐HCl buffer at pH 7.4, with 5% CH 3 CN (vol͞vol), at a finely controlled temperature of 25°C (k uncat ϭ 2.8 ϫ 10 Ϫ5 ⅐min…”

Determination of threshold adverse effect doses of percutaneous VX exposure in African green monkeys

“…Aliquots of the agent were placed into separate vials and refrigerated. Because undiluted VX is known to undergo autocatalytic hydrolysis (Yang et al, 1996), the purity of the agent was determined at the time of every exposure. That is, separate aliquots were opened for each exposure and a sample of the material, at the time of the exposure, was also analyzed by NMR.…”