The thermodynamics of hydration of phenols

Abstract

The solubilities and enthalpies of solution in water of 2-cresol and 4-cresol at 25 °C and the solubility of 4-t-butyl-phenol in water at four temperatures have been measured. The thermodynamic parameters for solution of the three phenols are combined with the parameters for sublimation to give information on the transfer of the phenols from the gas phase to aquous solution. The free energies of hydration of seven substituted phenols are linearly related to the Hammett σ-parameters for the substituents. Either electron accepting or donating substituents in phenol make the enthalpy of hydration more negative. The greater the dipole moment of the phenol the stronger is the attractive solute–solvent interaction. The increment to the entropy of ionization of phenol produced by alkyl substitution results from partial compensation of larger increments to the entropies of hydration of both the phenoxide anion and the neutral phenol.