Dielectric properties of liquid systems: study of interactions in the systems carbon tetrachloride with benzene, toluene, and p-xylene

Intermolecular associations in liquid systems of non-polar and slightly polar compounds were studied through excess molar volumes (VE M), and excess dielectric properties (e E and n2 E D ) for mixtures of carbon tetrachloride (CCl4) with benzene (C6H6), toluene (C6H5CH3), and p-xylene (p ðCH3Þ2C6H4). These excess properties were calculated from measurements of density (q), static permittivity (e), and refractive index (nD) over the whole range of concentrations, at 298.15 K. The values of the excess dielectric properties for these mixtures were fitted in two different ways, one through least squares using the Redlich–Kister equation and the other using a model developed to explain deviations from ideality. The first fit was found to be descriptive while the second gave the equilibrium constant values for the interaction products actually formed in the mixtures and the respective electronic polarizabilities and dipole moments, indicating the existence of interaction products. INTRODUCTION In previous work we studied the intermolecular associations in liquids through theoretical and experimental studies of the dielectric behavior of binary liquid mixtures [1–4]. In the present work on intermolecular associations in liquids we report measurements of permittivities, refractive indices, and densities for the CCl4 þ C6H6, + C6H5CH3, and + p ðCH3Þ2C6H4 mixtures over the whole range of concentrations at 298.15 K. These mixtures are of considerable interest because in them the departures from ideality stems not only from dispersion, dipolar, and inductive forces, but also from the specific interactions that lead to the formation of chargetransfer complexes between the vacant 3D level of the chlorine atom in CCl4 and the π cloud of the aromatic hydrocarbons [5, 6]. In particular the studies of the static permittivity of solutions, measured with high precision, has the advantage that the experimental values are very sensitive to the existence of different interaction products that may be formed in the mixtures [7]. The experimental values of density (q), static permittivity (e), and refractive index for sodium light (nD) can be used to calculate the molar excess volume (VE M), the excess static permittivity (eE), and the excess permittivity at optical frequency (n2 E D ) over the whole range of concentrations. The excess values for the various mixtures can then be fitted using the Redlich–Kister [8] relation, however this was found to be insufficient, being only descriptive, therefore a model was developed to explain the excess dielectric considering all species present in the mixtures [3]. This previously developed model, based on the additivity of the electrical susceptibilities of the species present in a solution, required the formation of complexes 1:1 in the three systems studied to explain the departures from the ideality. However in the system CCl4 þ C6H6 this did not seemed to be sufficient making it necessary consider the existence of another type of complex to explain the departure from the dielectric ideality. To perform the theoretical curve, the equilibrium constant values for the interaction products actually formed in the mixtures and the respective electronic polarizabilities and dipole moments can be randomly generated, in order to verify that the values obtained with this method are in concordance with those obtained from measurements of the enthalpy of mixing. It was expected that in this way the existence of other interaction product could be verified. EXPERIMENTAL SECTION Materials Reaction grade compounds were fractionally distilled twice and kept in dark bottles, under dry nitrogen. Benzene, toluene, and p-xylene were refluxed over metallic sodium. Purity was better than 99.9 mol% through gas phase chromatography. In all distillations only the middle fraction coming over at the reported boiling point and comprising about 70% was SOR-PHYS