Use of the scaled-particle theory for the determination of single ion standard free energy of transfer between solvents

Abstract

The tetraphenylboron extrathermodynamic assumption is one of the methods most often used for the evaluation of single ion standard thermodynamic functions of transfer between two solvents. We show in this article that the scaled-particle theory may be useful for discriminating among those solvents for which this extrathermodynamic assumption may be questionable because of strong solute–solvent interactions. Although no general rule is proposed, the tetraphenylboron assumption seems valid in the case of the free energy of transfer between water and solvents like methanol, ethanol, acetonitrile, and formamide; it should not be used in the case of the transfer to solvents like propylene carbonate, dimethylsulfoxide or sulfolane. The scaled-particle theory may also be used to predict within 20% the standard free energy of transfer of the tetraphenylboron ion between water and aqueous mixed solvents; examples are given for water–methanol and water–ethanol mixtures.