Isothermal liquid-vapour equilibria of mixtures containing organic compounds. 3. Excess Gibbs free energies of cyclohexane + a linear ether.

Abstract

Vapour-liquid equilibria of binary mixtures of cyclohexane with a linear mono-, di-, or triether (diethyl, dipropyl, dibutyl, methyl butyl, ethyl butyl ether, formaldehyde dimethyl acetal, formaldehyde diethyl acetal, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyleneglycol dimethyl ether) were determined at 298.15 K by head-space gas cromatographic analysis of the equilibrated vapour phase. Excess molar Gibbs energies, G E, for the investigated mixtures were obtained by a least-squares treatment of the equilibrium results (x–y). The G E values are positive for all the systems and increase with increasing the ratio of oxygen to carbon atoms in the ether molecule. There is clear evidence for the effect of position of the oxygen atom in the chain structure of monoethers as well as for the effect of distance of two -0- groups in diethers. The behaviour of the activity coefficients at infinite dilution and of the free energies of solvation as well as of molar excess entropies, obtained from G E and the known excess enthalpies, are briefly discussed. The experimental G E values are compared with the predictions of a group contribution model in the random-mixing approximation.