(Vapor + liquid) equilibria of binary mixtures containing light alcohols and ionic liquids

This work presents (vapor + liquid) equilibrium (VLE) of binary mixtures containing methanol or ethanol and three imidazolium based ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium acetate, and 1-butyl-3-methylimidazolium hydrogen sulfate. VLE measurements were carried out over the whole range of composition between (283.15 and 298.15) K using a static apparatus. Activity coefficients γ_i of these solvents in the ionic liquids have been determined from the VLE data and correlated using the NRTL model. The results show that the NRTL model can be applied successfully with systems containing ionic liquids.     

Efficient cyclodehydration of diethylene glycol in Brønsted acidic ionic liquids

Cyclodehydration of diethylene glycol using various Brønsted acidic ionic liquids as dual solvent-catalysts has been studied for the first time. Better results were obtained in the presence of 1-butyl-3-methylimidazolium hydrogen sulfate ([PSmim]HSO₄) compared with other Brønsted acidic ionic liquids. Effects of the reaction conditions such as reaction temperature, reaction time and molar ratio of ionic liquid to diethylene glycol have been investigated. High diethylene glycol conversion, 97.0 %, and high 1,4-dioxane selectivity, 89.3 %, were obtained in [PSmim]HSO₄ under optimum conditions. Hammett method was used to determine the acidity order of these ionic liquids and the results were consistent with the catalytic activities observed in the cyclodehydration reaction. Utilization of Brønsted acidic ionic liquids as dual solvent-catalysts has some advantages, e.g. high conversion of DEG, easy preparation and reuse of ionic liquids, avoiding toxic catalysts and solvents.     

Hydrogen gas yields in irradiated room-temperature ionic liquids

Yields of H₂ produced by electron beam irradiation were investigated in a series of room-temperature ionic liquids comprising 1-hexyl-3-methylimidazolium, 1-hexyl-4-(dimethylamino)pyridinium, 1-butyl-1-methylpyrrolidinium, triethylammonium or trioctyl(tetradecyl)phosphonium cations associated with bis(trifluoromethylsulfonyl)imide anion. The G(H₂) values ranged from 2.6×10⁻⁸ mol/J for the imidazolium and pyridinium-based ionic liquids to 2.5×10⁻⁷ mol/J for the phosphonium liquid. These results correlate well with yields of gaseous hydrogen in studies of nonionic aliphatic and aromatic organic compounds.     

Measurement and modeling of osmotic coefficients of aqueous solution of ionic liquids using vapor pressure osmometry method

Osmotic coefficients of binary mixtures containing an ionic liquid, (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIm]BF₄, 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIm]ES, and 1-butyl-3-methylimidazolium methyl sulfate, [BMIm]MS) with water were measured until about 3 molal concentrations using vapor pressure osmometry method (VPO) at temperature ranges 298.15–328.15 K and modeled using different electrolyte excess Gibbs free energy models including electrolyte non-random two liquids (NRTL), modified NRTL (MNRTL), mean spherical approximation NRTL (MSA-NRTL), non random factor (NRF), and extended Wilson models. The results show that osmotic coefficient data increase with increasing temperature. The calculated standard deviations of the studied systems show that the applicability of these models for the correlation of VLE properties of ionic liquid solutions. The average standard deviations for the models have the order σ(?) MNRTL < σ(?) Wilson < σ(?) NRTL < σ(?) MSA-NRTL < σ(?)NRF. The results show MNRTL model is able to reproduce experimental osmotic coefficients of aqueous solution of studied ionic liquids with good precision.     

Partial molar volumes of selected gases in some ionic liquids

The partial molar volume of a gas that is dissolved at high dilution in a solvent is required to express the influence of pressure on Henry's constant as well as to describe the volume change (expansion) of the liquid caused by the dissolved gas. The correlations of recently published experimental results for the solubility of some selected gases (CO₂, Xe, CH₄, CF₄, H₂, CO, O₂) in three imidazolium-based ionic liquids (1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][CH₃SO₄]), and 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf₂N])) determined by the synthetic method were re-evaluated by also considering the experimentally determined volumetric properties. The new evaluation does not change the published results for Henry's constants, but additionally yields reliable information on the partial molar volume of those gases in the mentioned ionic liquids at temperatures from about 293 to 413 K.     

Brønsted酸性离子液体中的二甘醇脱水环化反应

首次报道了Brønsted酸性离子液体介质中的二甘醇的脱水环化反应,考察了不同的离子液体、离子液体/二甘醇摩尔比、反应温度和时间对反应的影响。结果表明,Brønsted酸性离子液体作为反应介质能够促进脱水环化反应的有效进行,且在离子液体1-(3-磺酸根丙基)-3-甲基咪唑硫酸氢盐([SPmim]HSO4)中,二甘醇的转化率和1,4-二氧六环的选择性更高。采用Hammett指示剂法测定了离子液体的酸度函数H0,其酸性强弱顺序为[SPmim]HSO4 > [Bmim]HSO4 > [Amim]HSO4 > [Hmim]BF4> [Bmim]H2PO4 >[Amim]H2PO4 > [Hmim]Tsa,这与离子液体在脱水环化反应中的催化效果一致。当温度为170 ˚C,离子液体/二甘醇摩尔比为1:1时,二甘醇在[SPmim]HSO4中反应2 h,转化率可达到97.0%,1,4-二氧六环的选择性为89.3%。     

Partition coefficients of organic compounds in new imidazolium based ionic liquids using inverse gas chromatography

Partition coefficients of organic compounds in four ionic liquids: 1-ethanol-3-methylimidazolium tetrafluoroborate, 1-ethanol-3-methylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate were measured using inverse gas chromatography from 303.3 to 332.55 K. The influence of gas–liquid and gas–solid interfacial adsorption of different solutes on ionic liquids was also studied. Most of the polar solutes were retained largely by partition while light hydrocarbons were retained predominantly by interfacial adsorption on the ionic liquids studied in this work. The solvation characteristics of the ionic liquids were evaluated using the Abraham solvation parameter model.     

Biphasic ethylene polymerisation using 1-n-alkyl-3-methylimidazolium tetrachloroaluminate ionic liquid as a medium of the Cp2TiCl2 titanocene catalyst

A systematic analysis was performed on a series of 1-n-alkyl-3-methylimidazolium tetrachloroaluminates (where alkyl = ethyl, butyl, hexyl, and octyl), applied as a medium of the Cp₂TiCl₂ titanocene catalyst, to evaluate the influence of the physical properties of the ionic liquids on the polymerisation reaction carried out in the biphasic ionic liquid/hexane mode. Two alkylaluminium compounds, AlEtCl₂ and AlEt₂Cl, were used as activators. The influence of the activator/catalyst molar ratio on the performance of the ethylene polymerisation was determined for each ionic liquid studied. The best results were obtained using 1-n-octyl-3-methylimidazolium tetrachloroaluminate. For the titanocene catalyst immobilised in the ionic liquid, AlEtCl₂ turned out to be a better activator than AlEt₂Cl in our studies. The properties of the polyethylene product have also been presented.     

The Baeyer-Villiger oxidation of ketones with Oxone in the presence of ionic liquids as solvents

Cyclic and linear ketones were readily oxidised with Oxone^® at 40 °C in ionic liquids as solvents and short times (2.5-20 h), affording their corresponding lactones and esters in high yields (65-95%). Both, aprotic and protic ionic liquids were used. The best conversion of ketones and the highest yields of products were obtained with 1-buty-3-methylimidazolium tetrafluoroborate and 1-methylimidazolium acetate as solvents. These ionic liquids were also efficiently recycled in the Baeyer-Villiger reaction without significant loss of activity. Several factors, such as the partial solubility of KHSO₅ in the ionic liquid, its viscosity and the presence of a proton in protic ionic liquids, have an influence on the course of the reaction.     

Olefin epoxidations in the ionic liquid [C4mim][PF6] catalysed by oxodiperoxomolybdenum species in situ generated from molybdenum trioxide and urea–hydrogen peroxide: The synthesis and molecular structure of [Mo(O)(O2)2(4-MepyO)2]·H2O

Commercially available molybdenum(VI) compounds, including molybdenum trioxide, were successfully employed as catalyst precursors in the epoxidation of olefins with urea–hydrogen peroxide adduct (UHP) in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [C₄mim][PF₆]. After oxidation, the corresponding epoxides were isolated by extraction with diethyl ether. Additionally the ionic liquid–catalyst mixture was recycled and reused in further catalytic cycles. The catalytic species is assumed to be an oxodiperoxomolybdenum species which forms in situ. A representative complex of this type was thus isolated and characterised. Reaction of excess 4-methylpyridine-1-oxide (4-MepyO) with MoO₃ dissolved in aqueous hydrogen peroxide afforded [Mo(O)(O₂)₂(4-MepyO)₂]·H₂O (1) as yellow crystals. Compound 1, an active epoxidation catalyst, was subsequently characterised and its structure determined by X-ray crystallography.     

Vapor-liquid equilibria of ternary systems with 1-ethyl-3-methylimidazolium ethyl sulfate using headspace gas chromatography

Vapor-liquid equilibria (VLE) for two binary systems 1-propanol + water and methyl acetate + methanol, and the ternary mixtures with the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM]⁺[EtSO₄]⁻ as entrainer were measured by headspace gas chromatography. From the experimental VLE data, the influence of the ionic liquid on the separation factors was investigated. The experimental results for the ternary systems show that [EMIM]⁺[EtSO₄]⁻ has a great influence on the separation factors of the systems investigated. Furthermore, the experimental separation factors were compared with the predicted ones of other ionic liquids and conventional selective solvents using modified UNIFAC (Dortmund).     

Ternary (liquid + liquid) equilibria of the azeotrope (ethyl acetate + 2-propanol) with different ionic liquids at T = 298.15 K

Experimental (liquid + liquid) equilibria involving ionic liquids {1,3-dimethylimidazolium methyl sulfate (MMIM MeSO₄)}, {2-propanol + ethyl acetate + 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆)} and {2-propanol + ethyl acetate + 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF₆)} were carried out to separate the azeotropic mixture ethyl acetate and 2-propanol. Selectivity and distribution ratio values, derived from the tie-lines data, were presented in order to analyze the best separation solvent in a liquid extraction process. Experimental (liquid + liquid) equilibria data were compared with the correlated values obtained by means of the NRTL, Othmer-Tobias and Hand equations. These equations were verified to accurately correlate the experimental data.     

Density functional theory study on the –SO3H functionalized acidic ionic liquids

In this work, the structures of the –SO₃H functionalized acidic ionic liquid 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate ([C₃SO₃Hmim]HSO₄), including its precursor compound (zwitterion), cation, and cation–anion ion-pairs, were optimized systematically by the DFT theory at B3LYP/6-311++G** level, and their most stable geometries were obtained. The calculation results indicated that a great tendency to form strong intramolecular hydrogen bonds was present in the zwitterion, and this tendency was weakened in the cation that was the protonation product of zwitterion. The intramolecular hydrogen bonds and intermolecular hydrogen bonds coexisted in the ionic liquid, and they played an important role in the stability of the systems. The strongest interaction in the ionic liquid was found between the anion and the functional group. The transition state research and the intrinsic reaction coordinate analysis of the hydrogen transfer reaction showed that, when the cation and the anion interacted near the functional group by double O–H···O hydrogen bonds, the ionic liquid was inclined to exist in a form of the zwitterion and H₂SO₄.     

Solubilities of imidazolium-based ionic liquids in aqueous salt solutions at 298.15 K

The solubilities of ionic liquids in the ternary systems (ionic liquid + H₂O + inorganic salt) were reported at 298.15 K and atmospheric pressure. The examined ionic liquids are [C₄mim][PF₆] (1-n-butyl-3-methylimidazolium hexafluorophosphate), [C₈mim][PF₆] (1-n-octyl-3-methylimidazolium hexafluorophosphate), and [C₈mim][BF₄] (1-n-octyl-3-methylimidazolium tetrafluoroborate). The examined inorganic salts are the chloride-based salts (sodium chloride, lithium chloride, potassium chloride, and magnesium chloride) and the sodium-based salts (sodium thiocyanate, sodium nitrate, sodium trifluoroacetate, sodium bromide, sodium iodide, sodium perchlorate, sodium acetate, sodium hydroxide, sodium dihydrogen phosphate, sodium phosphate, sodium tetrafluoroborate, sodium sulfate, and sodium carbonate). The effects of the cations and the anions of the ionic liquids and of the inorganic salts on the solubility of the ionic liquids in the ternary solutions were systematically compared and discussed.     

Preparation of ionic liquid/silica nanocomposites possessing no weight loss characteristic after calcination at 800 °C

Tetraethoxysilane reacted with silica nanoparticles in the presence of a variety of ionic liquids such as phosphonium-, ammonium-, and imidazolium-type ionic liquids under alkaline conditions to afford the corresponding ionic liquid/silica nanocomposites with a good dispersibility and stability in numerous solvents. It was demonstrated that these ionic liquid nanocomposites can be classified into the nanocomposites possessing no weight loss and weight loss characteristics after calcination at 800 °C, respectively, according to the ionic liquid structures in the composites. The ionic liquids except for 1-ethyl-3-methylimidazolium hydrogen sulfate were found to afford the corresponding ionic liquid/silica nanocomposites possessing no weight loss characteristic even after calcination at 800 °C.

Enantioseparation of mandelic acid enantiomers in ionic liquid aqueous two-phase extraction systems

In the past decade, ionic liquids have received great attention owing to their potential as green solvent alternatives to conventional organic solvents. In this work, hydrophobic achiral ionic liquids (1-butyl-3-methylimidazolium-hexafluorophosphate([bmim][PF₆]), 1-octyl-3-methylimidazolium tetrafluoroborate([omim][BF₄])) were used as solvents in chiral liquid-liquid extraction separation of mandelic acid (MA) enantiomers with β-cyclodextrin (β-CD) derivatives as hydrophilic chiral selectors preferentially forming complexes with (R)-enantiomers. Factors affecting the separation efficiency were optimised, namely the type of the extraction solvents and β-CD derivatives, concentrations of the β-CD derivatives and MA enantiomers, pH, and temperature. Excellent enantioseparation of MA enantiomers was achieved in the ionic liquid aqueous two-phase extraction systems under the optimal conditions of pH 2.5 and temperature of 5°C with the maximum enantioselectivity (α) of 1.74. The experimental results demonstrated that the ionic liquid aqueous two-phase extraction systems with a β-CD derivative as the chiral selector have a strong chiral recognition ability, which might extend the application of ionic liquids in chiral separation.     

Lewis Superacidic Ionic Liquids with Tricoordinate Borenium Cations

The first examples of ionic liquids based on borenium cations, [BCl₂L]⁺, are reported. These compounds form highly Lewis acidic liquids under solvent‐free conditions. Their acidity was quantified by determining the Gutmann acceptor number (AN). Extremely high ANs were recorded (up to AN=182, δ_31P=120 ppm), demonstrating that these borenium ionic liquids are the strongest Lewis superacids reported to date, with the acidity enhanced by the ionic liquid environment.     

Isothermal vapour–liquid equilibria in the binary and ternary systems consisting of an ionic liquid, 1-propanol and CO2

Vapour–liquid equilibrium measurements for binary and ternary systems containing carbon dioxide, 1-propanol, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquids are presented in this work. The binary CO₂ + 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide system at 313.15 K at pressure range from 2 to 14.4 MPa was examined. The obtained phase envelop shows that even at low pressure of CO₂ the solubility of the gas in the ionic liquid is high. The ternary phase equilibria were studied at 313.15 K and pressures in the range from 9 to 12 MPa. The ternary phase diagrams show that higher CO₂ pressure diminishes the miscibility gap.     

Tunable synthesis of propylene glycol ether from methanol and propylene oxide under ambient pressure

A series of basic and acidic ionic liquids, 1-butyl-3-methylimidazolium hydroxide (BMIMOH), 1-acetyl-3-methylimidazolium chloride (AcMIMCl) and AcMIMCl-FeCl₃, or analogues of AcMIMCl, namely 1-potassium acetate-3-methylimidazolium chloride (KAcMIMCl), 1-potassium (sodium, ammonium) acetate-3-methylimidazolium hydroxides (KAcMIMOH, NaAcMIMOH and NH₄AcMIMOH), were prepared and used as catalysts for catalytic synthesis of propylene glycol ether via reaction of propylene oxide (PO) with methanol under mild reaction conditions. KAcMIMOH exhibited outstanding catalytic performance with 94.2% of conversion of PO and 99.1% of selectivity to 1-methoxy-2-propanol (MP-2) at 60°C and ambient pressure for 4 h. However, AcMIMCl-FeCl₃ showed a good catalysis performance with high selectivity to 2-methoxy-1-propanol (MP-1). The tunable synthesis of MP-2 or MP-1 catalyzed by basic compound KAcMIMOH or acidic ionic liquid AcMIMCl-FeCl₃ was realized.     

Extraction of rare earth elements with phosphoryl-containing lariat crown ether in the presence of ionic liquids

Interfacial distribution of rare earth elements (REE) La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y between aqueous solutions of their nitrates and solutions of the lariat crown ether 1,4,10,13-tetraoxa-7,16-diaza(diphenylphosphinylmethyl)cyclooctadecane in dichloroethane was studied in the presence of the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide. The stoichiometry of extracted complexes was determined; the effect of HNO₃ concentration in the aqueous phase and the nature of extractant and ionic liquid on the extraction efficiency of REE(III) was considered.