Solvent effects of water on the decarboxylation of o-phthalic acid in supercritical water

Water's effect on o-phthalic acid decarboxylation was studied by varying the pressure from (20 to 40) MPa at (380, 400, and 420) °C. The rate constants decreased with increasing pressure at (400 and 420) °C, but remained nearly constant at 380 °C. The trends at (400 and 420) °C were explained using Kirkwood theory, which proposed preferential solvation of the reactant over the transition state. The 380 °C trend was thought to be explained by solvent inhomogeneities and water's peculiar behavior near the critical point. Solvent inhomogeneities were most likely responsible when rates remained low despite low dielectric constant values. These inhomogeneities could have caused a higher local dielectric constant around the solute, suppressing the rate in a manner similar to the higher-pressure region. Water, according to these findings, has the greatest influence on the reaction via solvation.