Supercritical Hydration of Organic Compounds. The Potential of Mean Force for Benzene Dimer in Supercritical Water

The diminishing hydrophobic effect in supercritical water has been examined through Monte Carlo simulations. The free energy profile was obtained for the association of the benzene dimer in supercritical water at 400 °C and 350 atm via statistical perturbation theory. In this report, it is first demonstrated that the TIP4P model can provide an adequate description of supercritical water in these simulations. Then, comparison is made with previous results for the benzene dimer in liquid benzene and ambient water at 25 °C and 1 atm. The results indicate that there is no hydrophobic enhancement of binding between benzene molecules in supercritical water with a much weaker association constant than that in ambient aqueous solution. Analysis of the computed potential of mean force suggests that solvent molecules do not form stable clusters near the solute. However, solvent-solvent clustering appears to be widespread. These findings provide the basis for further characterization of the supercritical hydration of organic compounds and modeling of reaction mechanisms in supercritical fluids.