Characterization of 1-alkanol + strongly polar compound mixtures from thermophysical data and the application of the Kirkwood-Buff integrals and Kirkwood-Fröhlich formalisms

Abstract

Mixtures formed by 1-alkanol and one strongly polar compound, nitromethane (NM), ethanenitrile (EtN), dimethyl sulfoxide (DMSO, sulfolane (SULF), nitrobenzene (NTBz) or benzonitrile (BzCN), have been investigated on the basis of a set of thermophysical data, which includes: excess molar functions, enthalpies, H_m^E, Gibbs energies, G_m^E, entropies, TS_m^E, isobaric heat capacities, C_pm^E, volumes, V_m^E; liquid-liquid equilibria (LLE), excess permittivies and deviations from the linearity of dynamic viscosities. In addition, calculations have been conducted to determine the Kirkwood-Buff integrals and the Kirkwood correlations factors, g_K, of the investigated mixtures. In the former case, DISQUAC has been employed for modeling the needed vapor-liquid equilibria data. Many systems under consideration are characterized by dipolar interactions between like molecules as it is indicated by LLE data. In addition, in the diagram G_m^E vs. H_m^E, they are located between the lines G_m^E=H_m^E/2 andG_m^E=H_m^E, which is the region where systems such as n-alkanone, or linear organic carbonate, or N-methylpyrrolidone + alkane are encountered. Consequently, they have H_m^E> 0, C_pm^E> 0 andTS_m^E> 0. On the other hand, alkanol-solvent interactions, for mixtures with a fixed 1-alkanol, become weakened in the sequence: DMSO ≈ SULF > EtN > NM > BzCN > NTBz. In systems with a given solvent, such interactions become also weaker when the chain length of the 1-alkanol is increased. Interestingly, the considered mixtures also show strong structural effects. Results on Kirkwood-Buff integrals reveal that systems containing NM, or NTBz, or BzCN or SULF or the mixture 1-octanol + EtN, are characterized by interactions between like molecules, which is in agreement with the available LLE data for these solutions. For DMSO systems or mixtures formed by EtN and shorter 1-alkanols, the local mole fractions do not differ from the bulk ones and the mixture structure can be ascribed to orientational effects. In addition, our results indicate that nitriles are more preferred than nitroalkanes around a central alcohol molecule. Calculations on g_Kshow that, in terms of the mixture polarization, the systems are rather unstructured, and that this trend becomes more important when the 1-alkanol size increases in solutions with a given solvent.