Thermodynamics of hydrogen-bonded complex formation in chloroform + cyclic ether mixtures

Abstract

The molar excess enthalpies H E for the binary mixtures chloroform + oxolane, + 1,3-di-oxolane, +oxane, + 1,4-dioxane, and + 1,3-dioxane have been measured as a function of mole fraction at atmospheric pressure and 298.15 K using a Picker flow microcalorimeter. The imprecision at the maximum value of H E is about ±0.5%. Values of H E were strongly negative for all mixtures. The magnitude and the symmetry of the H E curves depended on ring size and number of oxygen atoms. These results and the literature vapour pressure data for the chloroform + oxolane, chloroform + 1,3-dioxolane, and chloroform + 1,4-dioxane mixtures have been analyzed with the ideal associated solution model. The A+ B+ AB+ AB 2 model, where complexes AB and AB 2 are expected to form by the simultaneous chemical equilibria A+B ⇄ AB and A+2B ⇄ AB 2, was used for the diether mixtures. The simpler association model A+ B+ AB with formation of the AB complex was employed for the monoether mixtures. The equilibrium constants and enthalpies of formation of the AB and AB 2 complexes have been calculated from this analysis.