Critical temperatures of mixtures of quasi-spherical molecules. Alicyclic hydrocarbons + benzene, + hexafluorobenzene and + perfluorocyclohexane

The critical temperatures Tmc of mixtures of cyclo-alkanes (C5-C8) with benzene, hexafluorobenzene and perfluorocyclohexane have been measured. The results have been compared with the “van der Waals” model proposed by Rowlinson and co-workers. The results are consistent with the unlike interactions between cyclo-alkane + benzene, hexafluorobenzene and perfluorocyclohexane being roughly independent of the cyclo-alkane but becoming increasingly “weak” in the order : benzene, hexafluorobenzene and perfluorocyclohexane. This order is supported by the excess thermodynamic properties of liquid mixtures and second virial coefficients of related mixtures. The unlike interaction energy parameters obtained from the critical temperature data have been compared with those derived from the excess free energy of mixing at equimole fraction. The agreement is fairly good. The possible importance of the lack of balance of non-central forces is briefly discussed.