Study on properties of ionic liquid based on ZnCl2 with 1-butyl-3-methylimidazolium chloride

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Abstract

An ionic liquid (IL) BMIZnCl3 has been synthesized by directly mixing zinc chloride (ZnCl2) and 1-butyl-3-methylimidazolium chloride (BMIC) with molar ratio 1/1 under a dry argon atmosphere. The density and surface tension of the IL in temperature range from 313.2 K to 343.2 K were determined. The value of thermal expansion coefficient and surface entropy were estimated by extrapolation. In terms of Glasser’s theory, the standard molar entropy and lattice energy of the IL were estimated. Using the methods of Kabo and Rebelo, the molar enthalpy of vaporization of the IL, ΔlgHm at T = 298 K and ΔlgHm at the hypothetical normal boiling point were estimated. The thermal expansion coefficient, α, calculated by the interstice model is of the same order of magnitude as the experimental value.

Introduction

An ionic liquid (IL) is an ionic compound, which exhibits ionic conductivity, and it is a liquid below T = 373 K [1]. Because of the great potential as “green” solvents, ionic liquids (ILs) have been attracting great interest in the last decade and have received extensive attention from the academic and industrial communities [1], [2], [3], [4], [5]. Though the ILs based on AlCl3 have been most widely studied, they were infrequently used as solvent systems due to their sensitivity to moisture and air [6], [7]. Recently, it is found that the ILs based on ZnCl2 constitute a new type of ionic liquid, air- and moisture-stable, friendly to the environment and with catalytic activity in many reactions [4], [8], [9], [10]. In addition, it can be very useful for the electro-deposition of pure metals and alloys [11], [12] and in other specialized fields [13], [14], [15]. As a continuation of our previous investigations of ionic liquids [16], [17], [18], this paper reports the synthesis of the ionic liquid BMIZnCl3 by directly mixing ZnCl2 and 1-butyl-3-methylimidazolium chloride (BMIC) with a molar ratio 1/1 under a dry argon atmosphere. In this paper, we adopted Lecocq’s viewpoint [19] viz.: IL compounds with molar ratio BMIC/ZnCl2 = 1/1 is BMIZnCl3. The density and surface tension of BMIZnCl3 were determined over the temperature range of 313.2 K to 343.2 K. The value of the thermal expansion coefficient and surface entropy were estimated by extrapolation. In terms of Glasser’s theory, the standard molar entropy and crystal energy of BMIZnCl3 were estimated [20]. Using the methods of Kabo [21] and Rebelo [22], the molar enthalpy of vaporization of the IL, ΔlgHm at T = 298 K and ΔlgHm at the hypothetical normal boiling point were obtained. In order to compare with experimental values, the thermal expansion coefficient was calculated by the interstice model [23], and their magnitude is of the same order.

Section snippets

Chemicals

The 1-methylimidazole (AR grade reagent), obtained from ACROS, and chlorobutane of AR grade reagent, obtained from Beijing Chemicals Co., were distilled under a nitrogen atmosphere before use. Ethyl acetate and acetonitrile were distilled and then stored over molecular sieves in tightly sealed glass bottles. Anhydrous ZnCl2 (mass fraction purity 0.9999) was purchased from Aldrich, opened in the glove box filled with dry argon, and used without further purification.

Preparation of BMIC/ZnCl2 ionic liquids

The BMIC

Density and surface tension measurements

The values of density, ρ, and surface tension, γ, of BMIZnCl3 are listed in table 1. Each value in table 1 is the average of three determinations. The experimental values of ln ρ against T were fitted by the method of least-squares and empirical equations ln ρ = 0.5271 to 5.36 · 104 (T/K) was obtained. See figure 1. The correlation coefficient, r = 0.999, and standard deviation, s = 1.8 · 104, of the linear fit were obtained. The slope of the fitting equation is the thermal expansion coefficient of BMIZnCl

Acknowledgements

This project was supported by NSFC (20473036) and Bureau of Liaoning Province (2004066C) PR China.

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