Densities, speeds of sound, and refractive indices for binary mixtures of 1-butyl-3-methylimidazolium methyl sulphate ionic liquid with alcohols at T = (298.15, 303.15, 308.15, and 313.15) K

doi:10.1016/j.jct.2012.08.030

The Journal of Chemical Thermodynamics

Volume 57, February 2013, Pages 238-247

https://doi.org/10.1016/j.jct.2012.08.030 Get rights and content

Abstract

Experimental densities, speeds of sound, and refractive indices of the binary mixtures {1-butyl-3-methylimidazolium methylsulphate ([BMIM]⁺[MeSO₄]⁻) + methanol, or 1-propanol, or 2-propanol, or 1-butanol} were measured over the whole range of composition at T = (298.15, 303.15, 308.15, and 313.15) K. From the experimental data, excess molar volumes, excess isentropic compressibilities, deviation in refractive indices and molar refractions were calculated. The excess molar volumes, change in isentropic compressibilities, and deviation in refractive indices were fitted by the Redlich–Kister smoothing polynomial. The Lorentz–Lorenz equation was applied to correlate the volumetric properties and predict the density or the refractive index of the binary mixtures. Results for these quantities have been discussed in terms of intermolecular interactions between the components of the mixtures. For all the systems studied, the excess molar volume and excess isentropic compressibility are negative, while the change in refractive index on mixing is always positive over the entire composition range and at all temperatures.

Highlights

► Densities, speed of sound, and refractive indices of (IL + an alcohol) measured. ► Excess molar volume and excess isentropic compressibility are negative. ► Change in refractive index on mixing is positive. ► Redlich–Kister smoothing polynomial was used to fit the derived properties. ► L–L equation correlated V_m^E and predicted the density or the refractive index.

Introduction

Ionic liquids (ILs) are a class of organic salts that are composed entirely of ions and have an extremely low vapour pressure [1], [2], [3]. The properties of ILs and their applications have been extensively detailed in many papers [4], [5], [6], [7], [8]. Alcohols are versatile solvents used in chemical and technological processes, are inexpensive and easily available at high purity [9].

Iglesias et al. [2] previously reported volumetric properties and refractive indices of binary mixtures of {([BMIM]⁺[MeSO₄]⁻) or ([BMIM]⁺[BF₄]⁻) + ethanol, or nitromethane, or 1,3-dicholoropropane, or ethylene glycol, or DEGEE} at T = 298.15 K and at atmospheric pressure throughout the entire composition range. González et al. [6] investigated the densities, dynamic viscosities, and refractive indices for the binary mixtures ([BMIM]⁺[MeSO₄]⁻ + water, or ethanol) at T = (298.15, 313.15, and 328.15) K. Pereiro and Rodríguez [10] determined experimental densities, speeds of sound, refractive indices for ([BMIM]⁺[MeSO₄]⁻ + ethanol) and calculated the excess molar volume, change in refractive index on mixing and deviation in isentropic compressibility at T = (293.15 to 303.15) K. Sibiya and Deenadayalu [11] studied the densities and excess molar volumes for the binary systems ([BMIM]⁺[MeSO₄]⁻ + methanol, or ethanol, or 1-propanol) at T = (298.15, 303.15, and 313.15) K. Domańska et al. [12] reported the densities and excess molar volumes at T = 298.15 K and at atmospheric pressure for the binary systems ([BMIM]⁺[MeSO₄]⁻ + methanol, or 1-butanol, or 1-hexanol, or 1-octanol, or 1-decanol, or water).

In this work, the densities, speed of sound, and refractive indices for the binary systems ([BMIM]⁺[MeSO₄]⁻ + methanol, or 1-propanol, or 2-propanol, or 1-butanol) were experimentally measured over the whole range of composition at T = (298.15, or 303.15, or 308.15, or 313.15) K. From the experimental data, derived properties such as the excess molar volume (V_m^E), excess isentropic compressibility (κ_S^E), deviation in refractive indices (Δn) and molar refractions (R) were calculated. The Redlich–Kister smoothing equation was used to fit the derived properties and the Lorentz–Lorenz equation was used to correlate the excess molar volume and predict the density or refractive index of the binary systems. This work is a continuation of our previous investigations on the thermodynamic properties of ILs with organic solvents [8], [11], [13], [14], [15], [16], [17], [18], [19], [20]. To our best knowledge, there are no measurements of all three physical properties, i.e., density, speed of sound, or refractive index for the binary systems studied in this work at the four temperatures in the literature. The structure of the ionic liquid used in this work is presented in figure 1.

Section snippets

Materials

The alcohols used in this work were purchased from Sigma Aldrich with mass fraction purity >0.995 for 1-propanol and 2-propanol, >0.999 for methanol and >0.99 for 1-butanol. The IL was supplied by Aldrich with a mass fraction purity >0.97. The IL and alcohols were used without any further purification. The water content in the IL was determined using a Metrohm Karl Fischer coulometer and found to be 0.0024 mol fraction. The IL and alcohols were stored in a desiccator with molecular sieves after

Results and discussion

Excess molar volumes, excess isentropic compressibilities, change in refractive indices on mixing, and molar refractions were calculated from the experimental data, as follows: $V_{m}^{E} = \frac{x_{1} M_{1} + x_{2} M_{2}}{ρ} - \frac{x_{1} M_{1}}{ρ_{1}} - \frac{x_{2} M_{2}}{ρ_{2}},$ $k_{S}^{E} = Δ ks (ϕ) - T [\sum_{i} ϕ_{i} {\frac{(α_{p, i}^{*})}{σ_{i}^{*}}}^{2} - {\frac{(\sum_{i} ϕ_{i} α_{p, i}^{*})}{\sum_{i} ϕ_{i} σ_{i}^{*}}}^{2}],$ $Δ n (ϕ) = n - \sum_{i = 1}^{2} ϕ_{i} n_{i},$ $R = (\frac{n^{2} - 1}{n^{2} + 2}) V_{m} .$

In these equations, x₁ and x₂ are the mole fractions, φ_i is the ideal volume fractions of the pure component i, M₁ and M₂ are the molar masses, ρ₁ and ρ₂ are the densities of the pure components, where 1 and 2 refer

Conclusion

In this paper, excess molar volume, excess isentropic compressibility, molar refraction and refractive index deviation for the binary systems ([BMIM]⁺[MeSO₄]⁻ + methanol, or 1-propanol, or 2-propanol, or 1-butanol) were calculated from the density, speed of sound, and refractive index data at T = (298.15, 303.15, 308.15, 313.15) K over the whole range of composition. For each system, V_m^E was negative and decreased slightly when the temperature increased. κ_S^E was negative for all systems and

Acknowledgements

The authors acknowledge funding from the Department of Science and Technology (SA) and the National Research Foundation (SA) for the purchase of the DSA 5000 M and Durban University of Technology for an M.Tech. scholarship for Sangeeta Singh. M. Aznar is the recipient of a CNPq (Brazil) fellowship.

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