Estimation of properties of the ionic liquid BMIZn₃Cl₇

Abstract

An ionic liquid (IL) BMIZn₃Cl₇ has been synthesized by directly mixing zinc chloride and 1-butyl-3-methylimidazolium chloride (BMIC) with molar ratio 3/1 under dry argon atmosphere according to the procedure of Lecocq and Abbott. The density and surface tension of the ionic liquid were measured in the temperature range from 318.2 to 343.2 ± 0.1 K. The estimation of physico-chemical properties of BMIZn₃Cl₇ was carried out. The thermal expansion coefficient and surface entropy were derived from the experimental data. In terms of Glasser's theory, the standard molar entropy and lattice energy of the ionic liquid were estimated. Using the methods of Kabo and Rebelo the molar enthalpy of vaporization of the ionic liquid, ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}°$ at 298 K and ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}°$ at the hypothetical normal boiling point were estimated. According to the interstice model, the calculated thermal expansion coefficient is in the same order of magnitude as the experimental value.

Introduction

Ionic Liquids (ILs) are ionic compounds, thus exhibiting ionic conductivity, and are liquids below 100 °C [1]. Because of their great potential as “green” solvents [2], [3] ionic liquids continue to attract much attention from both industrial and academic community [1], [2], [3], [4], [5]. Although the first generation of ILs based on AlCl₃ have been most widely studied, the ILs based on transitional metals were restricted in application due to their moisture- and air-sensitivity [6], [7]. In recent years, it is found that the ILs based on ZnCl₂ [8], [9] constitute a new type of ionic liquids which are air- and moisture-stable, friendly to the environment, with catalytic activity in many reactions [10], [11] and can be applied in other specialized fields [12], [13], [14], [15], [16], [17]. As a continuation of our previous research on ionic liquids based on transitional metals [18], [19], [20], [21], an ionic liquid compound BMIZn₃Cl₇ was synthesized by directly mixing ZnCl₂ and 1-butyl-3-methylimidazolium chloride (BMIC) with molar ratio 3/1 under dry argon atmosphere. According to the procedure of Lecocq et al. [8] and Abbott et al. [9], the volumetric and surface properties of the IL BMIZn₃Cl₇ were measured at temperature range of 318.2 to 343.2 ± 0.1 K. The thermal expansion coefficient and surface entropy of BMIZn₃Cl₇ were estimated by extrapolation of the experimental data. In terms of Glasser's theory [22], [23], the standard molar entropy and crystal energy of BMIZn₃Cl₇ were estimated. Using the methods of Kabo and co-workers [24] and Rebelo et al. [25] the molar enthalpy of vaporization of the IL, ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}°$ at 298 K and ${\mathrm{\Delta }}_{\text{l}}^{\text{g}}{H}_{\text{m}}°$ at the hypothetical normal boiling point were estimated. The thermal expansion coefficient, α, calculated using the interstice model [21], [26] was in the same order of magnitude as the experimental value.