Solubility of nonelectrolytes in polar solvents III: Alkyl p-aminobenzoates in polar and mixed solvents.

The relative solubilities of n-alkyl p-aminobenzoates in water, proplyene blycol-water mixtures, proplyene glycol, and several other pharmaceutically important solvents can be predicted on the basis of a theoretical equation. This equation relates the activity coefficient of the hydrophobic portion of the molecule to the product of its surface area and its interfacial tension [free energy per unit area of a hydrocarbon (tetradecane) against the polar or semipolar solvent of interest]. The assumptions, conclusions, and applicability of the theorectical relationship are compared to those of the Scatchard-Hildebrand approach.