Hydrates of Organic Compounds. I. Solid-Liquid Phase Equilibria in the Water+1,4-Dioxane System and Some Properties of 1,4-Dioxane Hydrate

The solid-liquid phase diagram for the water +1,4-dioxane system has been determined by the ordinary cooling curve method and with the aid of a differential scanning calorimeter (DSC). The diagram shows the existence of a hydrate which is stable in rather narrow ranges of temperature (−15.8∼−13.5 °C) and of composition (37.0∼46.5 wt% dioxane). From the phase relations and an analysis of the calorimetric data, the composition and the heat of formation (from the liquid states of both components) of the hydrate have been estimated to be C4H8O2·mH2O with m=36∼39 and ΔH1=−51.3 (for m=36)∼−55.6 (for m=39) kcal/mol respectively. This hydrate seems to be the same as that recently reported by Rosso et al., though the compositions and the temperature ranges are very different.