Solvent effects on a Diels-Alder reaction in supercritical water: RISM-SCF study

A Diels-Alder reaction in supercritical water is studied by means of combined electronic structure and liquid state theories. The target system is the cycloaddition of cyclopentadiene with methyl vinyl ketone. The rate and the yield of the reaction in supercritical water are calculated and compared with those in ambient water. The activation free energies of the two isomers, cis and trans, are compared. The results are in agreement with the experimentally observed increase of the rate and the yield. The solvation effect for the rate constant is decreased in supercritical water, but the rate is increased because of the thermal excitation rather than the solvation effect. The trans-conformer has shown less activation energy in ambient water and supercritical water compared to the cis-conformer. The estimated yield in supercritical water is more than 600 times higher than in ambient water. The high yield in supercritical water is due to the high solubility of the reactants to supercritical water.