DECOUPLING SUBSTITUENT AND SOLVENT EFFECTS DURING HYDROLYSIS OF SUBSTITUTED ANISOLES IN SUPERCRITICAL WATER

The kinetics of hydrolysis in supercritical water of a series of substituted anisoles to methanol and the corresponding substituted phenol probed the coupling of solvent and substituent effects. For supercritical water concentrations [H2O] less-than-or-equal-to 3 mol/L, the substituent effects exhibited compelling correlation according to the classic Hammett formalism. For [H2O] > 5 mol/L, however, the Hammett correlation had an internal minimum at sigma = 0, indicative of rate acceleration by both electron-withdrawing and electron-donating substituents. The solvent and substituent effects were thus defined to be "decoupled" for [H2O] less-than-or-equal-to 3 mol/L, where the dielectric constant epsilon less-than-or-equal-to 1.28. The hydrolysis Hammett reaction constant increased with decreasing water density. The reaction constant was also of opposite sign to reported values for pyrolysis of substituted benzyl phenyl ethers, suggesting that the practical significance of the present work is the ability to design a substituent-specific solvent effect for selective hydrolysis or pyrolysis.