Enthalpies and Gibbs free energies of solvation in ethylene glycol at 298 K: Influence of the solvophobic effect

Abstract

Enthalpies of solution of low-polar substances: aliphatic and aromatic hydrocarbons, including alkanes, cycloalkanes, alkylbenzenes, naphthalene, biphenyl, and halobenzenes in ethylene glycol were measured at temperature T=298.15K using semi-adiabatic solution calorimetry. For some of these systems, previously unknown values of limiting activity coefficients were also determined using GC headspace analysis. Consideration of compensation plots of the Gibbs free energy vs enthalpy of solvation shows that the behavior of solutions in ethylene glycol is different from that of solutions in non-associated aprotic solvents. The Gibbs energies of solvation are significantly increased relative to the enthalpies, which is the sign of the solvophobic effect. The contribution of the solvophobic effect into the Gibbs energies of solvation of various substances was quantified using an extrathermodynamic approach. A linear correlation between this quantity and a molecular volume of dissolved compound was found. The solvophobic effect in ethylene glycol is stronger than in monohydric alcohols, weaker than in formamide and much weaker than in water. It is also entropy-driven and does not affect the enthalpies of solution of the studied substances in ethylene glycol.