The estimation of solubility in binary solvents: application of the reduced 3-suffix solubility equation to ethanol-water mixtures.

The reduced 3-suffix solubility equation (R3SSE) is applied to the characterization of solubility in the ethanol-water system. The data needed are the solubility of the compound in each of the pure solvents and at one ethanol-water composition. This composition has been estimated from solubility data to be 0.56 volume fraction of ethanol. The solubility obtained at this volume fraction is used to estimate the ternary solute-solvent interaction constant, C2. The R3SSE, with the C2 thus obtained, predicts the mixed solvent solubilities of the compounds tested, as accurately as that obtained from several volume fractions. The superiority of the R3SSE over two related equations--a simple second-degree polynomial equation and a simplified form of the R3SSE which neglects contributions to solubility from the solvent mixture--is also demonstrated for a number of solutes.