Volumetric properties of ionic liquid 1,3-dimethylimidazolium methyl sulfate + molecular solvents at T = (298.15–328.15) K
Introduction
One of the most important types of organic salts is ionic liquids (ILs), which are liquids at or near room temperature in their pure state. They have been widely used in a number of fields in both academia and industry and exhibit many advantages such as a low melting point (<373 K), a wide liquid range, suitable viscosity, thermal stability, ability to dissolve a variety of materials and most important, negligible vapor pressure [1], [2], [3]. Ionic liquids have been suggested as green and benign replacements for traditional volatile organic solvents and a growing number of applications such as catalysis, chemical reactions, separations, electrochemistry, and nanoscience investigations [4], [5], [6]. These developments demand reliable reference data on the thermodynamic and thermophysical properties of their mixtures with other compounds. These properties of ionic liquids depend on structural factory, ion-association and ion–solvation effects, are receiving increasing interest and are being studied more systematically. It is very important to understand the interactions between the traditional solvents and ionic liquids, which can be accomplished by the measurements of the physical properties.
Binary mixtures of ionic liquids with molecular solvents have been used in many processes mainly for synthesis, design of chemical, extractive processes, and heat transfer mediate involving ionic liquids on an industrial scale. To date, a number of papers have measured some of the thermodynamic and thermophysical properties of binary mixtures systems containing an ionic liquid in molecular solvents such as density, viscosity, speed of sound, surface tension, thermal conductivity and phase equilibria [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. These papers mainly report these quantities for the whole composition range of ionic liquids in solvents, and only some other works have been performed for dilute region solution of ionic liquids. It is well known that ionic liquids can be viewed as kind of organic electrolyte. Therefore, at even higher dilutions, ionic liquid acts a conventional but rather strongly associated electrolyte [17]. Therefore, electrolyte solution models may treat their properties.
The most commonly studied ionic liquids are based on the imidazolium cation and fluorinated anions such as BF4−, PF6−, NTf− and so on. However, the hydrolytical instability of such anions has become obvious, and decomposition of these fluorinated anions leads to the formation of highly toxic and corrosive HF, the use of these ionic liquids will be limited. Therefore, the synthesis and application of halogen free ionic liquids is necessary. Several types of these systems have been described, e.g. alkyl sulfunates, organoborates and alkyl sulfate anions. The most important properties of alkyl sulfate based ionic liquids are easily synthesis, using cheap alkylating agent, solvent free synthesis, high reaction rate, excellent purity, large scale synthesis, safe and nontoxic chemical, low viscosities and low melting points [18].
One of the most important ionic liquid based on methyl sulfate anion is 1,3-dimethylimidazolium methyl sulfate. Activity coefficients at infinite dilution of various solutes in the ionic liquid, [MMIm]MSO4, were measured [19]. The surface tensions were measured in a series of alcoholic solutions of [MMIm]MSO4 [20]. The osmotic coefficient of [MMIm]MSO4 has also been measured with water by Macedo and co-workers [21], [22]. The liquid–liquid equilibria of several binary system containing [MMIm]MSO4 and dialkyl carbonates, ketones or acetates and other solvents were studied and similar studies were made on alkyl sulfate containing ionic liquids [23], [24], [25], [26], [27], [28], [29], [30], [31].
In this work, the procedure to synthesize [MMIm]MSO4 is described and volumetric properties of binary mixtures containing this ionic liquid and molecular solvents have been studied. Volumetric properties have been extensively studied in order to know the nature and extent of various intermolecular interactions existing between different species present in mixture [32]. In this work densities were measured for the binary mixtures containing an ionic liquid, 1,3-dimethylimidazolium methyl sulfate, [MMIm]MSO4 with water, N,N-dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile (MeCN), and methanol (MeOH) at T = (298.15–328.15) K and at atmospheric pressure from which the values for infinite dilution apparent molar volumes are calculated with the help of Redlich–Mayer [33].
Section snippets
Materials
The chemicals used for this work were N-methylimidazole (>99%), dimethyl sulfate (>99%), toluene (GR, >99%), N,N-dimethylsulfoxide (GR, >99.5%), N,N-dimethylformamide (GR, >99.5%), acetonitrile (GR, >99.8%), and methanol (GR, >99.8%) in mass fraction purchased from Merck. N-methylimidazole was freshly distilled at reduced pressure and other reagents were used without further purification. The doubly distilled deionised water was freshly used for preparation of solutions, which had conductivity
Results and discussion
The experimental density, d, values as function of ionic liquid concentration, m, for binary mixtures, [MMIm]MSO4 + methanol, + water, + DMSO, + DMF, and + MeCN at T = (298.15–328.15) K are reported in Table 2. The apparent molar volumes, Vϕ of [MMIm]MSO4 in the studied solvents were calculated from the densities of the solutions using the following equationwhere m is molality of [MMIm]MSO4 in binary mixtures, d and d0 are densities of ionic liquid solution and pure solvent,
Conclusions
Experimental density data were measured for the systems containing an ionic liquid [MMIm]MSO4 with water, methanol, N,N-dimethylsulfoxide, acetonitrile, and N,N-dimethylformamide at T = (298.15–328.15) K. From these data apparent molar volumes were calculated and fitted to the Redlich–Mayer. It was found that Redlich–Mayer equation is suitable for both the dilute region and the agreement between the limiting values for apparent molar volumes. The values of have the following order in the
Acknowledgement
The author wishes to thank the graduate Council of the University of Mohaghegh Ardabili for financial support.
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