An extended Johnson–Furter equation to salting-out phase separation of aqueous solution of water-miscible organic solvents

The Johnson–Furter equation, which correlates the salt effects on relative volatility changes of components in a binary mixture at presence of salt, is extended to salting-out phase separation phenomenon observed in aqueous solutions of some water-miscible organic solvents. The extended equation quantitatively correlates partitions of components of the ternary mixture, namely, the organic solvent, water, and the salt between the salted-out two phases, and is successfully applied to five ternary mixtures including acetonitrile–H2O–LiCl, –NaCl, –KCl, acetone–H2O–NaCl, and 2-propanol–H2O–NaCl where salting-out phase separation occurs. A molecular mechanism of salting-out phase separation as salt-solvent and solvent–solvent interactions is also discussed by using Kirkwood–Buff solution theory.