Density, speed of sound, refractive index and relative permittivity of methanol, propan-1-ol or pentan-1-ol + aniline liquid mixtures. Application of the Kirkwood-Fröhlich model

Abstract

Densities (ρ) and speeds of sound (c) at a temperature T = 298.15 K, relative permittivities at 1 MHz (ε_r) and refractive indices at the sodium D-line (n_D) at T = (293.15 K to 303.15 K), all of them at a pressure p = 0.1 MPa, are reported for binary liquid mixtures alkan-1-ol + aniline. The alkan-1-ols considered are methanol, propan-1-ol and pentan-1-ol. Also, the values of the excess molar volume (V_m^E), excess isentropic compressibility (κ_S^E), excess speed of sound (c^E), excess refractive index (n_D^E), excess relative permittivity (ε_r^E) and its temperature derivative ((∂ε_r^E)⁄∂T )_p are calculated and fitted to Redlich-Kister polynomials. The agreement among the reported data and other literature sources is analysed by comparing V_m^E, n_D^E, ε_r^E and the deviation of c from mole-fraction linearity (Δc). The positive excess molar internal energies at constant volume (U_(m,V)^E) show the dominance of the breaking of interactions between like molecules in the energy balance on mixing, particularly the breaking of strong dipolar interactions between aniline molecules. This contribution is also dominant for the ε_r^E values, as they are negative and decrease with the length of the alkan-1-ol chain. Calculations on the concentration-concentration structure factor are consistent with these statements, revealing homocoordination in the studied systems. The V_m^E are negative, which together with the positive U_(m,V)^E indicate the existence of important structural effects in the studied mixtures. The application of the Kirkwood-Fröhlich model shows that the average relative orientation of neighbouring dipoles is similar in the mixtures methanol + aniline or + pyridine, in spite of the different character of the predominant interactions in the latter mixture (heterocoordination).