Densities and viscosities of binary mixtures of magnetic ionic liquids 1-alkyl-3-methylimidazolium tetrachloroferrate with ethyl acetate at temperatures (293.15 to 323.15) K
Introduction
Magnetic ionic liquids (MILs) as a subclass of ionic liquids (ILs) have attracted considerable attention over the past decade, as they can combine the unique properties of ILs with magnetic, photo-physical or catalytic properties that originate from the metal incorporated in the complex anion [1]. Since the first MIL [Bmim][FeCl4] was synthesized by Hayashi in 2004, more MILs have been reported in the literatures [2], [3], [4], [5]. The paramagnetic properties are mainly induced by the transition metal containing anions, lanthanide complexes in anions or organic radical ions. For example, Del Sesto presented a series of MILs with transition metal (such as iron Fe(III), cobalt Co(II) and manganese Mn(II)) containing anions [6]. Mudring subsequently explored dysprosium based MILs with luminescence and strong response to magnetic fields [7].
Among all these MILs, 1-alkyl-3-methylimidazolium tetrachloroferrate has been extensively studied in various application areas. As the solvent and oxidant, [Bmim][FeCl4] can be used in the polymerization of conducting polymers, leading to the formation of uniform nanospheres with relatively narrow size distributions (50–100 nm) [8], [9], [10]. This MIL also exhibits high catalytic activity for varied reactions, such as synthesis of 1,2-azidoalcohols, esterification of oleic acid to biodiesel and depolymerization of poly(ethylene terephthalate) [11], [12], [13]. Furthermore, [Bmim][FeCl4] has also been successfully applied as solvent to extract asphaltenes from coal direct liquefaction residues and [Hmim][FeCl4] can effectively extract triazine herbicides from vegetable oils [14], [15]. On the grounds of magnetic property of MIL, they have the potential to open up new application areas because of their easy separation and efficient recyclability.
Despite the wide applications of MILs in the laboratory, they have not been implemented at commercial scales yet, partially due to their high viscosities. Although it is true that the viscosity could be decreased by forming magnetic anions, still MILs have typically several orders of magnitude higher viscosity than the conventional organic solvent. A combination of the MILs with other low viscous components can be considered as an alternative. Ethyl acetate (EA) is one organic solvent with low viscosity, low cost, low toxicity and agreeable odor and it can be applied as solvents in liquid-liquid extraction, such as aromatics removal from pyrolytic oil fractions [16], [17]. Thus using EA as co-solvent is one option in MILs applications to reduce the viscosity. EA has been employed as a dispersing solvent for the extracting solvent MIL in the technique of dispersive liquid-liquid microextraction, and further used as diluent for MIL phase to reduce its viscosity prior to analysis [18]. The densities and viscosities of some pure MILs have been studied by several researchers and the results were summarized in a review paper [1]. To the best of our knowledge, no study has been reported for the binary or tertiary mixtures of MILs and organic solvents. Yet investigation on the physicochemical properties of the binary mixtures of MILs is essential for further application of MILs and also for industrial process designs.
In the present work, three MILs [Bmim][FeCl4], [Hmim][FeCl4] and [Omim][FeCl4] were synthesized and characterized with 1H NMR and Raman spectroscopy. The densities and viscosities of three binary systems, [Bmim][FeCl4] + EA, [Hmim][FeCl4] + EA and [Omim][FeCl4] + EA, were measured over the whole range of compositions at temperatures (293.15 to 323.15) K at atmospheric pressure. The molar volume and the thermal expansion coefficient of the pure MILs were calculated from the experimental densities. The densities and viscosities of these mixtures as a function of temperature were correlated using linear equation and VFT equations, respectively. In the end, the excess molar volumes (VE) and viscosity deviations (Δη) were calculated and fitted to the Redlich-Kister equation. The intermolecular interactions were discussed as well.
Section snippets
Materials
Ethyl acetate (> 99.5%), Iron(III) chloride (anhydrous, 98%), 1-chlorobutane (> 98%), 1-chlorohexane (> 98%) and 1-chlorooctane (> 98%) were supplied by Chemical Reagent Beijing Company Limited. 1-methylimidazole (> 98%) was obtained from Beijing Donghua Rio Tinto Technology Development Company Limited.
Preparation of MILs [Bmim][FeCl4], [Hmim][FeCl4] and [Omim][FeCl4]
[Bmim][FeCl4] was prepared via two steps [2]. Firstly, the intermediate 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was synthesized by reacting 1-methylimidazole (0.20 mol) with 1-chlorobutane (0.24
Characterization of MILs
The cationic structures of the intermediates [Bmim]Cl, [Hmim]Cl and [Omim]Cl and their purities were primarily confirmed with the 1H NMR spectra. The data of 1H NMR spectra are presented in Table 1 and the results show that the aimed intermediates have been synthesized successfully, as the ratio of the integral peak area are in agreement with the ratio of the number of the hydrogen atoms at different chemical shift, and there are no additional peaks appearing.
Since the MILs can disturb the NMR
Conclusions
The densities and viscosities of three binary mixtures for [Bmim][FeCl4] + EA. [Hmim][FeCl4] + EA and [Omim][FeCl4] + EA were measured over the entire composition range from 293.15 K to 323.15 K at 5 K intervals and at atmospheric pressure. The results showed that densities and viscosities presented a decreasing trend with temperature increasing or with mole fraction of EA increasing. Therefore, adding low viscous organic solvent EA to MIL indeed can obtain desirable physicochemical properties of binary
Acknowledgements
This research was supported financially by the National Natural Scientific Fund of China (No. 21376242, No. 21336002, No. 21476234). Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-JSC011) and the Fund of State Key Laboratory of Multiphase Complex Systems, IPE, CAS (No. MPCS-2015-A-05).
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