CRITICAL SOLUTION TEMPERATURES OF LIQUID-MIXTURES AND THE HYDROPHOBIC EFFECT

Two important generalizations applicable to liquid pairs that exhibit critical solution temperatures (CST) are the Prigogine rule (CST will occur at equimolar component compositions) and the Timmermans rule (an additive that is preferentially soluble in one component of the liquid pair will reduce the mutual solubility). We show that, while these rules are obeyed by organic liquid pairs, they are violated by aqueous binary systems. Contrary to the Prigogine rule, the CSTs of aqueous binaries occur at high water mole fractions, and contrary to the Timmermans rule, globular protein denaturants and Hofmeister ions solubilize the second liquid in water. We trace these violations to the structure of water and the hydrophobic effect. © 1979 American Chemical Society.