Thermodynamics of mixtures containing oxaalkanes. 6. Random mixing in ether + benzene, or + toluene systems

The Flory model has been applied to linear or cyclic ether + benzene, or +toluene mixtures. In addition, the relative variation of the molar excess enthalpy, HmE, along homologous series of the considered systems, has been discussed taking into account the contributions to HmE from the ether-ether, aromatic-aromatic and ether-aromatic interactions. It has been shown that in CH3(CH2)u-1O(CH2CH2O)v(CH2)u-1CH3 + benzene mixtures, the u increase (v fixed) leads to a weakening of interactions between unlike molecules, and that proximity effects also weaken this type of interactions. In contrast, the v increase (u fixed) or cyclization lead to stronger interactions between unlike molecules. From the application of the model, it is concluded that the random mixing hypothesis may be considered to be valid to a large extent for many of the investigated solutions. Erroneously, strong orientational effects are predicted for 1,3-dioxolane, or 1,4-dioxane + benzene systems, but this has been attributed to the model can not describe asymmetric HmE curves when the mixture compounds show close values for Vi (molar volume) and for Vi* (reduction parameter for volume). Previous calculations on the basis of the Kirkwood-Buff integrals formalism confirm that the mixture structure is close to random mixing. Flory results on the excess molar volumes have been discussed taking into account the so-called curvature and P* contributions to this excess function.