Solid-liquid phase diagram of the binary system pyridine + sulfolane

Abstract

Abstract Solid-liquid equilibrium temperatures were measured for the binary system pyridine(1) + sulfolane(2) over the entire composition range 0 ⩽ x ⩽ 1. Solid solutions were observed in the region in which solutions are in equilibrium with mesomorphic sulfolane (crystal I) and a partition coefficient (K = 0.88) was calculated. The phase diagram exhibits a eutectic at T = 216.4 K and x2 = 0.257. For solutions in equilibrium with sulfolane ordinary crystal II, an equation was elaborated for calculating the activities of sulfolane by a series expansion of initial freezing point depressions XXX. This equation was found to be capable of reproducing values of x within a few p.p.h. over a very large temperature range: 290.23-216.4 K. On this basis the binary system pyridine(1) + sulfolane(2) may be classified as a “regular” system, in which low enthalpies of mixing counterbalance excess entropies to minimize the excess free energy. This is also in accordance with our previous measurements of other excess properties (ϵE, VE, etc.).