Reaction Mechanism of Nerve-Agent Hydrolysis with the Cs8Nb6O19 Lindqvist Hexaniobate Catalyst

Abstract

We present a detailed mechanism for the hydrolysis of Sarin catalyzed by Cs8Nb6O19 obtained using electronic structure calculations. The initial steps of the reaction involve the adsorption of water and Sarin on the hexaniobate catalyst via nonbonding interactions. Dissociation of the coordinated water molecule generates a hydroxide ion that adds nucleophilically to the coadsorbed Sarin molecule in a concerted manner, following a general base catalysis mechanism. The addition of OH– to the nerve agent generates a trigonal bipyramidal pentacoordinated phosphorus intermediate that subsequently undergoes facile dissociation forming either HF or isopropanol and a corresponding phosphonic acid. The rate-determining step of the overall reaction is found to be the dissociation of water on the catalyst in concert with the nucleophilic addition of the nascent OH– to the nerve agent. The calculated barrier for this step is considerably smaller than that measured for bulk base hydrolysis. This work represents a blue...