Thermodynamics of mixtures containing alkoxyethanols. Part XV.? DISQUAC characterization of systems of alkoxyethanols with n-alkanes or cyclohexane?

Physical Chemistry Chemical Physics Pub Date: 2001-06-20 DOI: 10.1039/B100765N

Abstract

Binary mixtures of alkoxyethanols, CH3–(CH2)n–O–(CH2CH2O)mOH, and n-alkanes or cyclohexane are characterized in terms of DISQUAC. The corresponding dispersive (DIS) and quasichemical (QUAC) interchange coefficients, Ceh,lDIS/QUAC, for the (e,h) contacts (type e, –O–; type h, –OH) are given. In comparison with the values for 1-alkanol + monooxalkane systems, the proximity effects in CH3–(CH2)n–O–CH2–CH2–OH + n-alkane mixtures lead to an increase in the Ceh,lDIS and Ceh,lQUAC (l = 1,2) coefficients and to a decrease in Ceh,2DIS. For other hydroxyethers (3-methoxypropanol, 4-methoxybutanol), the Ceh,lQUAC (l = 1,2) coefficients approach those of 1-alkanol + monooxalkane mixtures with increasing separation between the –O– and OH– groups. However, the Ceh,2DIS coefficient is still lower than in alcoholic solutions, indicating that proximity effects in the framework of DISQUAC remain. DISQUAC yields a consistent description of the vapor–liquid equilibria, VLE, and of liquid–liquid equilibria, LLE. Good results are obtained for azeotropic data. The coordinates of the critical points are represented over a reasonable range of composition and temperature. Excess molar enthalpies HmE and the excess molar heat capacity at constant pressure, CpmE, are well reproduced. The typical large deviations for properties at infinite dilution, excess molar partial enthalpies, HmE,∞, and natural logarithms of activity coefficients, ln γi∞, of the associated compound are found. Thermodynamic properties of alkoxyethanol + alkane mixtures are determined by the self-association of the polar compound [italic v (to differentiate from Times ital nu)]ia both inter- and intramolecular H-bonds, as well as by dipole–dipole interactions between alkoxyethanol molecules. These interactions are analyzed in terms of the effective dipole moments ([small mu, Greek, macron]) and are more important than in 1-alkanol + alkane mixtures. The dipole–dipole interactions in systems with alkoxyethanols decrease along a homologous series, and are enhanced by the presence of two ether atoms. Intramolecular H-bonds are more relevant than the intermolecular H-bonds and become weakened with the separation between the –O– and –OH groups of the hydroxyethers.

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