Thermodynamics of solutions of iodine and perfluorocarbons in cycloalkanes

The solubilities of iodine from 9 to 30°C were measured in the C₅, C₆, C₇, C₈, and C₁₀ cycloalkanes. The solubilities were found to increase smoothly with ring size and to be greater than these of corresponding n-alkane. The results are analyzed in terms of the solubility parameter version of the regular solution theory and, unlike the n-alkanes, good agreement is found suggesting that the cycloalkanes are good model substances for testing theoretical predictions of the effect of molecular size on the thermodynamics of liquid mixtures and that molecular shape and flexibility need not be considered, at least in equilibrium properties governed by the free energy. A similar analysis of the upper critical solution temperatures of cyloalkane + perfluorotributylamine, cycloalkane + perfluorocyclohexane, and n-alkane + perfluorotributylamine mixtures leads to the same conclusion.