A Continuum Solvation Model Including Electrostriction:  Application to the Anisole Hydrolysis Reaction in Supercritical Water

Abstract

We present a simple and efficient method for calculating the effect of electrostriction on the solvation of molecular species. This new method introduces solvent compressibility into the standard continuum dielectric description of the solvent. It is based on a numerical grid-based algorithm for solving Poisson's equation and is therefore applicable to arbitrary charge distributions in cavities of arbitrary shape. Application to the anisole hydrolysis reaction in supercritical water shows that the effects of solvent compression can be large; for example, compression is observed to lower the free energy barrier to reaction by as much as 14 kcal/mol. Additionally, compression effects are found to qualitatively alter the pressure dependence of the reactivity. Finally, the inclusion of compression effects is shown to bring the calculated pressure dependence of the activation barrier into significantly better agreement with experiment.

Pressure Effects on Friedel–Crafts Alkylation Reactions in Supercritical Difluoromethane

“…[40] Tucker and co-workers have shown that local density of water molecules increases around the methoxy group for the hydrolysis of anisole in supercritical water. [41] Repeating the same experiment in liquid dichloroethane at 90 8C and ambient pressure using 0.16 m Anisole and t-butyl chloride and p-Tos (0.08 m) yielded 32 % conversion with 30 % ortho-and 70 % para-substituted product, which is similar to CH 2 F 2 at a 50-bar pressure. Repeating the experiment using cyclohexane as the solvent led to a lower overall yield (8 %) but exclusively para-substituted product.…”

Theoretical study on the dimerization of Si(OH)4 in aqueous solution and its dependence on temperature and dielectric constant

“…It is clear from many studies (e.g., Liu et al, 2003) that ions in supercritical aqueous solutions essentially create local environments with higher effective dielectric constants than the bulk value for those T, P conditions. However the simulations of Luo and Tucker (1996) on anisole hydrolysis in supercritical water suggest that such effects are much smaller for neutral molecules than for ions. One term we have not yet considered is the P⌬V contribution to the enthalpy.…”

A case against large cluster-induced nonequilibrium solvent effects in supercritical water

“…We use a completely compressible (CC) continuum electrostatic model, described elsewhere [4,32], to represent a charged solute/SCW system. From this model we can extract both the structureless equilibrium solvent density distribution around the solute, qrY and the equilibrium Gibbs free energy of solvation Dq CC 3.…”

“…The ®nal ®eld, i x Y where x denotes the IC, CC or PC() model, is given by the solution of Poisson's equation with self-consistent values for the ®eld-dependent local dielectric constant x i x rY within the constraints of model x. The free energy of charging the solute in the presence of a model x solvent is then written in terms of the ®nal ®eld i x as [3,4,32,35] …”