Neutral hydrolyses of carbon disulfide: An ab initio study of water catalysis

The water-catalyzed hydrolysis reaction of carbon disulfide (CS(2)) has been investigated at the levels of HF and MP2 with the basis set of 6-311++G(d,p) using the combined supramolecular/continuum models, in which up to six water molecules are involved in the hydrolysis and the effect of water bulk solvent is taken into account according to the polarizable continuum model (PCM). The activation Gibbs free energies in water solution, DeltaG(sol) (not equal) (298 K), for the rate-determining steps of one up to six water hydrolyses are 247.9, 184.2, 152.3, 141.8, 134.4, and 118.9 kJ/mol, respectively. The most favorable hydrolysis path of CS(2) involves a sort of eight-membered ring transition structure formed by six water molecules, among which three water molecules are not involved in the proton transfer, two near to the nonreactive sulfur atom, and one below the parent carbon disulfide. This suggests that the hydrolysis of CS(2) can be mediated with the water molecule(s) and be significantly facilitated by the cooperative effects of the water molecule(s) in the nonreactive region. The catalytic effects of water molecule(s) due to the alleviation of ring strain in the proton transfer process may result from the synergistic effects of rehybridization and charge reorganization from the prereaction complex to the rate-determining transition state structure induced by water molecule(s). PCM solvation models could significantly lower the rate-determining activation Gibbs free energies by 20-38 kJ/mol when two up to six explicit water molecules involved in the neutral hydrolysis of CS(2).