Densities, Refractive Indices and Excess Properties of Binary Mixtures of Acetonitrile with Benzene, Toluene, m-Xylene and Mesitylene at Temperatures from (298.15 to 313.15) K

Abstract

The densities () and refractive indices (n D) of binary mixtures of acetonitrile with benzene, toluene, m-xylene and mesitylene including those of pure liquids, over the entire composition range expressed by mole fraction x 1 of acetonitrile were measured at temperatures (298.15, 303.15, 308.15, and 313.15) K under atmospheric pressure. From the experimental data, the excess molar volumes (E m V) and the deviations in refractive indices (Δn) were calculated. These results are fit to a Redlich-Kister type polynomial equation. The results indicate the presence of weak interactions between acetonitrile and aromatic hydrocarbon molecules. The deviations in E m V values follow the order toluene < benzene < m-xylene < mesitylene. The results are discussed in terms of the intermolecular interactions. Introduction Studies of physicochemical properties of binary mixtures are of considerable importance in the fundamental understanding of the nature of the interactions between unlike molecules. In recent years there has been considerable interest in theoretical and experimental investigations of the excess thermodynamic properties of binary mixtures [1-3]. Refractive index and density measurements are expected to shed some light on both solvent-solvent and solute-solvent interactions [4]. The excess properties of binary liquid mixtures are important for understanding and interpreting the interactions between molecules of a mixture [5]. In this work, The densities and refractive indices of binary mixtures of acetonitrile with benzene, toluene, m-xylene and mesitylene at temperatures (298.15, 303.15,308.15, and 313.15) K were studied. The Redlich-Kister equation was used to correct and fit the experimental excess molar volumes and the refractive index deviations. The variation of these parameters with the composition and temperature of the mixtures has been discussed in terms of the molecular interactions in these mixtures. The effect of the number and position of the methyl groups in these aromatic hydrocarbons on molecular interactions in these mixtures has also been discussed. A survey of the literature shows that very few measurements have been made on the densities and refractive indices of binary mixtures for acetonitrile + aromatic hydrocarbons. Afaf H. Absood [6] report densities of these binary systems at 303.15K. Nevertheless, to our knowledge, no literature data on densities and refractive indices are available for this system. Experimental Chemicals: Acetonitrile, mesitylene (Fluka AG, mole fraction purity > 0.998), benzene, toluene and m-xylene (Merck, mole fraction purity > 0.995) were used without further purification. All liquids were stored over freshly activated molecular sieves of type 4A (union Carbide). Doubly distilled water was used as the standard liquid with conductivity less than 0.05 µs cm 1. Apparatus and Procedure: The mixtures were prepared by mass and were kept in special airtight stopper glass bottles to avoid evaporation. The weightings were done using an electronic balance (model GR-202R, AND, Japan) with a precision of ± 0.01 mg. The uncertainty in the mole fraction was estimated to be less than ± 0.0001. The density measurements of the pure solvents and the mixtures were performed by means of an Anton Paar, model DMA 48, Graz, Austria with a precision of ±0.00005 g cm-3 , between 298.15 and 313.15 K. The DMA cell was calibrated with dry air and doubly distilled water at atmospheric pressure. The sample size was 0.70 cm 3