SOLVENT EFFECTS ON CHEMICAL PROCESSES .6. THE PHENOMENOLOGICAL MODEL APPLIED TO THE SOLUBILITY OF NAPHTHALENE AND 4-NITROANILINE IN BINARY AQUEOUS-ORGANIC SOLVENT MIXTURES

The phenomenological theory of solvent effects on solubility partition s the free energy of solution into contributions from solvent-solvent interactions (the general medium or solvophobic effect), solvent-solut e interactions (the solvation effect), and solute-solute interactions (the intersolute effect). The theory relates the solvent effect on sol ubility to the mole fractions of the solvent components and the model parameters K1 and K2 (which are stepwise solvation exchange constants) and gA (the general medium parameter, where g is a curvature correcti on factor to the surface tension, and A is the nonpolar surface area o f the solute). Solubility data for naphthalene and 4-nitroaniline are given over the entire composition range in aqueous-organic mixtures, t he organic cosolvents being methanol, ethanol, propan-2-ol, propane-1, 2-diol, ethylene glycol, acetone, dimethyl sulfoxide and acetonitrile. The data are quantitatively described by the model. Cosolvents are cl assified, on the basis of their polarities (as measured by their octan -1-ol-water partition coefficient P), into a less polar class whose so lvation exchange constants increase with log P, and a more hydrophilic class with the opposite tendency. The gA parameter can be reasonably predicted with the empirical relationship gA = -33.4 log P(M) + 13.4 l og P(R) (angstrom2 mol-1), where M and R refer to the organic cosolven t and the solute, respectively. The product g(gamma2 - gamma1), where gamma2, and gamma1 are the surface tensions of pure cosolvent and wate r, respectively, is close to the dispersion surface energy component o f water and many other solvents.