Thermodynamics of solvation in propylene glycol and methyl cellosolve

• Experimental values of limiting activity coefficients in propylene glycol and methyl cellosolve are reported.
• Gibbs free energy versus enthalpy of solvation plots show the presence of the solvophobic effects in studied solutions.
• The solvophobic effect in propylene glycol is as strong as in methanol.
• The solvophobic effect in methyl cellosolve is rather weak and can be compared to that in butanol.

Limiting activity coefficients of low-polar substances: aliphatic and aromatic hydrocarbons, including alkanes, cycloalkanes, alkylbenzenes, and halobenzenes in two solvents, propylene glycol and methyl cellosolve, were measured at temperature T = 298.15 K using gas chromatographic headspace analysis technique. The Gibbs free energies of solvation were calculated from these data and analyzed together with the enthalpies of solvation for the same systems. It was shown that the Gibbs free energies of solvation in propylene glycol are significantly lower than in its homologue ethylene glycol, and in methyl cellosolve they are lower than in propylene glycol. This difference is mainly due to the solvophobic effect, which strength is decreasing in the same order: ethylene glycol > propylene glycol > methyl cellosolve. The contribution of the solvophobic effect into the Gibbs free energies of solvation can be determined using a Gibbs free energy versus enthalpy of solvation plot. This contribution is shown to grow up linearly with the molecular volume of a solute in propylene glycol and methyl cellosolve, as well as in ethylene glycol and in monohydric alcohols.