Abstract
The partition coefficients, Kmim, of N-methylimidazole (mim) in two-component systems composed of ionic liquid (IL) and a series of organic solvents immiscible with ILs (butyl acetate, ethyl acetate, tert-butyl methyl ether, diethyl ether and cyclohexane) were determined by a shake-flask method. The influence of different factors such as temperature, solvent polarity, mim concentration, and water content on Kmim by using 1-butyl-3-methylimidazolium chloride {[C4C1im]Cl} as a model compound was comprehensively studied. The calculated thermodynamic functions of transfer (∆trG0, ∆trH0, ∆trS0) showed that the mim migration (IL→organic phase) is a thermodynamically unfavorable and enthalpy-determined process in the temperature range of 298.15 to 328.15K; however, the results suggested that mim partition toward the organic phase can be enhanced by the rational manipulation of the extraction conditions. Experiments conducted with other 1-alkyl-3-methylimidazolim chlorides (CnC1im]Cl (n = 6, 8, 10) revealed that mim possesses similar behavior and can be successfully washed out from the ILs by extraction with organic solvents. The results obtained in this study give some clues toward the choice of an appropriate solvent and conditions to be employed for the purification of halide-based ILs by means of a liquid-liquid extraction.
Highlights
The interest in ionic liquids (ILs) has been continuously growing in the last two decades due to their unique properties and high potential as “green” alternatives to conventional harmful organic solvents [1,2,3,4,5,6]
The solvents used for this experiments were butyl acetate, ethyl acetate, tert-butyl methyl ether, and cyclohexane, and [C4 C1 im]Cl was the model IL
As it can be seen, the extraction ability of the solvents is consistent with the results presented above, i.e., the mim partition into the organic phase is facilitated by an organic solvent with higher polarity according to the following order: BuOAc < EtOAc < MTBE ≈ Et2 O < cyclohexane
Summary
The interest in ionic liquids (ILs) has been continuously growing in the last two decades due to their unique properties and high potential as “green” alternatives to conventional harmful organic solvents [1,2,3,4,5,6]. The approach most applied for the synthesis of ILs is based on the quaternization reaction between appropriate N-, S-, or P-containing compounds and haloalkanes (mainly chlorides and bromides) followed by metathesis reaction in order for the halide anion to be further exchanged [15]. In this way, the production of halide-based ILs of high purity is a precondition for purer ILs to be obtained at the end of the reaction scheme. This first step is conducted at temperatures up to Processes 2017, 5, 52; doi:10.3390/pr5040052 www.mdpi.com/journal/processes
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