Solvophobic effects in the mixtures of inorganic salts and organic solvents

Abstract

The effect of inorganic salts on the solvation properties of organic solvents is analyzed. Experimental data on the thermodynamic functions of solvation at 298.15 K for alkanes and aromatic hydrocarbons in methanol and tetrahydrofuran at varying concentrations of sodium iodide or lithium bromide have been obtained. The solubility of apolar compounds decreases with growing salt concentration as the Gibbs free energy of solvation linearly increases with the salt molarity. Hence, the salt effects in non-aqueous solvents can be characterized with Sechenov constants like those in aqueous solutions. An increase in salt concentration leads to a decrease in the entropy of hydrocarbon solvation. Calculation of the thermodynamic functions of cavity formation in the studied systems based on the molecular dynamics data show that the salt effects can be attributed to a less favorable and lower-entropy cavity formation. The Gibbs free energy of cavity formation is also linear on the salt concentration. These results can be interpreted as strengthening of the solvophobic effects upon salt addition, similar to what is typical for aqueous solutions. The observed trends are also similar to the behavior of solvation free energies in ionic liquids, which are known to correlate with ion concentration.