Thermodynamic properties of binary mixtures containing cyclic ethers

Abstract

Molar excess enthalpies H E for binary mixtures (1,1,1-trichloroethane + oxolane, + oxane, + 1,3-dioxolane, + 1,3-dioxane and + 1,4-dioxane) were measured using a Picker flow microcalorimeter. For the 1,3-dioxolane mixture they were small and positive, H E(x 1 = 0.5) = 45 J mol −1 , whereas for all the other systems they were negative, H E(x 1 = 0.5) from −100 J mol −1 to −650 J mol −1. Their magnitude depended on the cycle size and the number of their oxygen atoms in the cycloether ring, as well as relative position. The latter can also influence the symmetry of the curves. These results, together with those quoted in the literature on vapour-liquid equilibrium for cyclic ether + n-alkane and 1,1,1-trichloroethane + n-alkane, were interpreted in terms of molecular surface interactions using the Dispersive-Quasichemical model (DISQUAC), which is an extension of the quasichemical theory. The interchange energy coefficients in the quasichemical approximation (C quac st,1 and C quac st,2) and in the zero approximation (C disp st,1 and C disp st,2) were calculated for each contact (s, t). The DISQUAC model provided a fairly consistent description of molar excess enthalpies in function of concentration for all the binary mixtures investigated.