Abstract
The solubility of β-cyclodextrin (β-CD) in ionic liquids (ILs) and the activity coefficients at infinite dilution ( ) of more than 20 solutes (alkanes, aromatic hydrocarbons, alcohols) were measured in four chosen ionic liquids, their mixtures with β-CD, and in the β-CD at high temperatures from 338 to 398 K using the inverse gas chromatography. The intermolecular interactions, inclusion complexes and the possible increasing of the solubility of β-CD in water using the IL are presented. The solubility of β-CD in ten chosen hydrophobic ILs at the temperature T = 423 K was detected. The solid-liquid phase diagrams (SLE) of {IL (1) + β-CD (2)} binary systems at the high mole fraction of the IL were measured for three systems (1-ethyl-3-methylimidazolium chloride, [EMIM][Cl], 1-ethyl-3-methylimidazolium bromide, [EMIM][Br]; and for 1-butyl-3-methylimidazolium chloride, [BMIM][Cl]). The eutectic points were determined at the high IL concentration for all binary systems. The intermolecular interaction and the possibility of inclusion complexes of the IL and/or solvents with β-CD were discussed. The infrared spectroscopy, IR was used for the description of the intermolecular interactions in the (β-CD + IL) systems. It was shown via the activity coefficients at infinite dilution results that the inclusion complexes are dependent on the temperature. The addition of β-CD to the IL does not improve the selectivity of the separation of the aliphatics from aromatics.
Highlights
Numerous compounds–supramolecular guests of different shape and polarity, ions, and even radicals are known to form stable inclusion complexes with β-cyclodextrin (β-CD), a well-known host molecules [1,2,3,4,5,6,7,8]
The ionic liquids (ILs) chosen in this work were expected to have the possibility of forming inclusion complexes with β-CD and to be better solvents than many other because of their differences in polarity and the specific interaction possibilities
The solutes used for the measurements of activity coefficients at infinite dilution were purchased from Sigma-Aldrich, 0.98+ and were used without the further purification because the GLC technique separated any impurities on the column
Summary
Numerous compounds–supramolecular guests of different shape and polarity, ions, and even radicals are known to form stable inclusion complexes with β-cyclodextrin (β-CD), a well-known host molecules [1,2,3,4,5,6,7,8]. Its relatively non-polar cavity is capable of forming inclusion complexes with a variety of molecules. The interaction of β-CD with one component monolayer of cholesterol mixtures has been investigated in the aqueous sub-phase [11] This cyclic molecule forms a cone-shaped cavity with hydrophilic outer and a relatively hydrophobic inner surfaces [12]. Imidazolium-based ILs with a different anion are treated as a novel solvents with interesting properties, which can be used as an entrainers in the separation processes for the several mixtures [15,16,19,20]. The solubility and conductivity measurements were used in aqueous solutions of β-CD and 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] [24]. Different mechanism of inclusion complexes with the guest is discussed
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