Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 2009-03-05

Theoretical study of the neutral hydrolysis of hydrogen isocyanate in aqueous solution via assisted-concerted mechanisms.

S Tolosa Arroyo, A Hidalgo Garcia, J A Sansón Martín

Index: J. Phys. Chem. A 113(9) , 1858-63, (2009)

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Abstract

A procedure is described for the theoretical study of chemical reactions in solution by means of molecular dynamics simulation, with solute-solvent interaction potentials derived from ab initio quantum calculations. We apply the procedure to the case of neutral hydrogen isocyanate hydrolysis, HNCO + 2 H(2)O --> H(2)NCOOH + H(2)O, in aqueous solution, via the assisted-concerted mechanisms and the two-water model. We used the solvent as a reaction coordinate and the free-energy curves for the calculation of the properties related to the reaction mechanisms, with a particular focus on the reaction and activation energies. The results showed that the mechanism with two water molecules attacking the C=N bond is preferred to the mechanism with three waters forming a ring of eight members. In addition, the aqueous medium significantly reduces the activation barrier (DeltaG(double dagger) = 13.9 kcal/mol) and makes the process more exothermic (DeltaG = -11.1 kcal/mol) relative to the gas-phase reaction, increasing the rate constant of the process to k = 4.25 x 10(5) s(-1).