Hydrophobic effect at the origin of the low solubility of inert solid substances in hydrogen-bonded solvents.

The new solubility equation derived from the thermodynamics of mobile order in liquids is used to predict the solubility of four solid aliphatic and aromatic hydrocarbons, namely, tricosane, octacosane, biphenyl and pyrene, in nonassociated and hydrogen-bonded solvents. The analysis of the relative importance of the different terms contributing to the solubility shows that (1) the fluidization of the solute always represents a barrier to the solubility, (2) in non-hydrogen-bonded solvents, the solubility essentially results from the balance of the exchange entropy correction and the change in the nonspecific cohesion forces upon mixing, (3) in alcohols or in water, the solubility is mainly determined by the hydrophobic effect which corresponds to a solute rejecting effect of the solvent. This effect is responsible for the lower solubility values of the inert substances in associated solvents with respect to those in nonassociated solvents.