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

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, C_eh,l^DIS/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 C_eh,l^DIS and C_eh,l^QUAC (l = 1,2) coefficients and to a decrease in C_eh,2^DIS. For other hydroxyethers (3-methoxypropanol, 4-methoxybutanol), the C_eh,l^QUAC (l = 1,2) coefficients approach those of 1-alkanol + monooxalkane mixtures with increasing separation between the –O– and OH– groups. However, the C_eh,2^DIS 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 H_m^E and the excess molar heat capacity at constant pressure, C_pm^E, are well reproduced. The typical large deviations for properties at infinite dilution, excess molar partial enthalpies, H_m^E,∞, and natural logarithms of activity coefficients, ln γ_i^∞, of the associated compound are found. Thermodynamic properties of alkoxyethanol + alkane mixtures are determined by the self-association of the polar compound 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 () 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.