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A Computational Study of Detoxification of Lewisite Warfare Agents by British Anti-lewisite: Catalytic Effects of Water and Ammonia on Reaction Mechanism and Kinetics

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journal contribution
posted on 25.04.2013, 00:00 by Chandan Sahu, Srimanta Pakhira, Kaushik Sen, Abhijit K. Das
trans-2-Chlorovinyldichloroarsine (lewisite, L agent, Lew-I) acts as a blistering agents. British anti-lewisite (BAL, 2,3-dimercaptopropanol) has long been used as an L-agent antidote. The main reaction channels for the detoxification proceed via breaking of As–Cl bonds and formation of As–S bonds, producing stable, nontoxic ring product [(2-methyl-1,3,2-dithiarsolan-4-yl)­methanol]. M06-2X/GENECP calculations have been carried out to establish the enhanced rate of detoxification mechanism in the presence of NH3 and H2O catalysts in both gas and solvent phases, which has been modeled by use of the polarized continuum model (PCM). In addition, natural bond orbital (NBO) and atoms in molecules (AIM) analysis have been performed to characterize the intermolecular hydrogen bonding in the transition states. Transition-state theory (TST) calculation establishes that the rates of NH3-catalyzed (2.88 × 10–11 s–1) and H2O-catalyzed (2.42 × 10–11 s–1) reactions are reasonably faster than the uncatalyzed detoxification (5.44 × 10–13 s–1). The results obtained by these techniques give new insight into the mechanism of the detoxification process, identification and thermodynamic characterization of the relevant stationary species, the proposal of alternative paths on modeled potential energy surfaces for uncatalyzed reaction, and the rationalization of the mechanistic role played by catalysts and solvents.