Ionic Liquids in Polyethylene Glycol Aqueous Solutions: Salting-in and Salting-out Effects

Summary. Changes of the fluid phase behaviour of polyethylene glycol (PEG) aqueous solutions – viz. critical solution temperature shifts at atmospheric pressure – were produced by the addition of different ionic liquids, namely 1-ethyl-3-methylimidazolium ethyl sulfate and 1-alkyl-3-methylimidazolium chloride (alkyl = ethyl to decyl). The addition of ionic liquids with long alkyl chains improves the solubility of PEG in water (salting-in effect), whereas the impact of short-chain ionic liquids is usually the contrary (salting-out effect). The results are interpreted taking into account the kosmotropic (water-structuring) or chaotropic (water-structure-breaking) nature of ionic liquids, as compared to other inorganic salts.     

Synthesis of derivatives of prenylacetic acids by reactions of alkyl malonate, cyanoacetate, and acetoacetate with alkylating reagents in ionic liquids

A method for the synthesis of carboxylic acid derivatives containing one or two —CH₂CH _n (Me)CH _n+1CH₂— fragments (n = 0, 1) was developed. The method is based on the alkylation of (di)alkyl malonates, cyanoacetates, and acetoacetates with acyclic prenyl halides in ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate. For the ambident ethyl acetoacetate anion, the reactions with prenyl halides devoid of a double bond in the allylic position relative to the halogen atom carried out in the ionic liquids give mixtures of C- and O-alkylation products, while in the case of allylic prenyl halides, only C-alkylation products are formed. The reactions of ethyl 2-geranylmalonate and 2-geranylacetoacetate with bromocyclohexane and 1-chloro-3-dimethylaminopropane in ionic liquids provided derivatives of pharmacologically active geranylacetic acids. The product yields are higher than those in molecular organic solvents. The ionic liquids were recovered and reused in the alkylation.     

Electrochemical behavior of aluminum and some of its alloys in chloroaluminate ionic liquids: electrolytic extraction and electrorefining

The electrochemical behaviors of pure Al, Al–6%Si, Al–3%Cu, and Al–3.7%Cu–0.9%Mg–0.8%Pb–0.6%Fe alloys were investigated in the chloroaluminate ionic liquids 1-butyl-3-methylimidazolium chloride [BMIm]Cl/AlCl₃ (40/60 mol%) and 1-ethyl-3-methylimidazolium chloride [EMIm]Cl/AlCl₃ (40/60 mol%). Electrolytic extraction of copper from Al–Cu alloys in the employed ionic liquids was explored. The alloys were anodically dissolved in the ionic liquids and then pure copper was recovered under potentiostatic conditions. Due to the large difference between the deposition potentials of Cu and Al, pure Cu can be obtained without Al contamination. Electrorefining of Al–3%Cu and Al–6%Si alloys was also investigated in [BMIm]Cl/AlCl₃ (40/60 mol%) at room temperature. High purity aluminum deposits were obtained with significantly low energy consumption of about 2 kWh/kg of Al.     

Electrospray ionization mass spectrometry of ionic liquids and determination of their solubility in water

Electrospray ionization mass spectrometry is used to detect both the cations (C⁺) and the anions (A^–) of ionic liquids (CA). In this study, the ionic liquids are diluted with aqueous methanol before injection. In addition to the main peaks of the parent ions, fragmentation products are observed upon increasing the cone voltage, whereas aggregates of the parent ion with one or more ionic liquid molecules (e.g., C(CA)_n⁺, A(CA)_n^–) are observed upon decreasing the cone voltage. The ions of several ionic liquids in a mixture are also detected and the ratios of their concentrations estimated. A method is developed to determine quantitatively the concentration of an ionic liquid in solution by using the cation and anion of another ionic liquid as internal standards. By using this method, the solubilities in water at room temperature (22±1 °C) of three typical hydrophobic ionic liquids have been determined: 0.70±0.08 g L^–1 for methyltributylammonium bis(trifluoromethylsulfonyl)imide (MeBu₃NNTf₂), 6.0±0.5 g L^–1 for butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyrNTf₂), and 18.6±0.7 g L^–1 for 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆).     

Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids with ɛ–β-fish-like phase diagram

The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr), or 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced interfacial layer (A ^S), and the solubilities of ionic liquid (S ^O) and alcohol (A ^O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion stabilized by both C₁₂mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained.     

Synthesis and biological evaluation of some novel 1-alkyl-3-methylimidazolium carboxylate ionic liquids as potential antifungal agents

In an effort to discover lead compounds that may be of importance as potent antifungal agents, a series of novel 1-alkyl-3-methylimidazolium carboxylate ionic liquids were efficiently synthesized through a solvent-free ultrasound-assisted quaternization reaction of 1-methylimidazole and alkyl bromides RBr (R = hexyl, octyl) followed by an anion exchange process with selected carboxylate anions (cinnamate, salicylate, crotonate, and oxalate). Quantitative yields obtained were in the range of 86–94%. Structure characterization was done using FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopic techniques. All the synthesized compounds showed in vitro antifungal activity against the fungus Candida albicans with the minimum inhibitory concentrations found to be less than or equal to 1%. Preliminary cytotoxicity assays (trypan blue exclusion and MTT) were performed on all ionic liquids and findings revealed higher lymphocyte viability in 1-hexyl-3-methylimidazolium carboxylate ionic liquids than in 1-octyl-3-methylimidazolium counterparts. No extensive toxicity effect was observed with the carboxylate anion variation. Among the tested compounds, 1-hexyl-3-methylimidazolium crotonate and 1-hexyl-3-methylimidazolium oxalate exhibited the lowest cytotoxicity in the trypan blue exclusion and MTT assays, respectively. Together, our results highlight the potential of carboxylate-based ionic liquids in the development of next-generation antifungal drugs.     

Extraction of Metal Ions from Aqueous Solutions Using Imidazolium Based Ionic Liquids

This article represents a step towards how to choose an ionic liquid as the solvent to improve metal ion (Ag⁺ and Pb²⁺) extraction. The liquid-liquid solvent extraction is proposed with the following imidazolium ionic liquids (ILs): 1-ethyl-3-ethylimidazolium, or 1-butyl-3-ethylimidazolium, or 1-hexyl-3-ethylimidazolium bis{(trifluoromethyl)sylfonyl}imide [EEIM][NTf₂], or [BEIM][NTf₂], or [HEIM][NTf₂], or 1-butyl-3-ethylimidazolium hexafluorophosphate [BEIM][PF₆], or 1-hexyl-3-ethylimidazolium hexafluorophosphate [HEIM][PF₆] and the popular 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] for comparison. The effect of anion type (NTf₂⁻ versus PF₆⁻) and the effect of structural components of an ionic liquid including alkyl chain length at the cation and the ethyl substituent instead methyl at the cation, on the extraction and re-extraction processes by using dithizone as a metal chelator, were studied at 296 K. Dithizone was employed to form neutral metal-dithizone complexes with heavy metal ions to extract them from aqueous solution into the ILs. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users. Presented at the 236th ACS National Meeting, August 17–21, Philadelphia, USA.     

Surface active and aggregation behavior of methylimidazolium-based ionic liquids of type [Cnmim] [X], n?=?4, 6, 8 and [X]?=?Cl?, Br?, and I? in water

The surface active and aggregation behavior of ionic liquids of type [C _n mim][X] (1-alkyl-3-methylimidazolium (mim) halides), where n = 4, 6, 8 and [X] = Cl⁻, Br⁻ and I⁻ was investigated by using three techniques: surface tension, ¹H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS). A series of parameters including critical aggregation concentrations (CAC), surface active parameters and thermodynamic parameters of aggregation were calculated. The ¹H NMR chemical shifts and SANS measurements reveal no evidence of aggregates for the short-chain 1-butylmim halides in water and however small oblate ellipsoidal shaped aggregates are formed by ionic liquids with 1-hexyl and 1-octyl chains. Analysis of SANS data analysis at higher concentrations of [C₈mim][Cl] showed that the microstructures consist of cubically packed molecules probably through π–π and hydrogen bond interactions.     

Binary Mixtures of Aprotic and Protic Ionic Liquids Demonstrate Synergistic Polarity Effect: An Unusual Observation

In this communication, we demonstrate the solute–solvent and solvent–solvent interactions in the binary mixtures of two aprotic ionic liquids, namely 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, with the protic ionic liquid 1-methylimidazolium acetate. The synergistic effects as expressed by the solvatochromic parameter are noted. This observation is in contrast to the mixing of protic ionic liquids 1-methylpyrrolidium acetate and 4-methylmorpholine acetate with 1-methylimidazolium acetate, respectively. It appears that the synergistic effects in the binary mixtures of aprotic and protic ionic liquids are caused by the formation of hydrogen bonds, since cations are dominant H-bond donors while anions are dominant H-bond acceptors. Preferential solvation models are used to describe the solute–solvent interactions in the binary ionic liquid mixtures.     

Imidazolium ionic liquids as bifunctional materials (morphology controller and pre-catalyst) for the preparation of xerogel silica’s

This article describes the preparation of xerogel silica’s by the sol–gel technique in the presence of the ionic liquids (ILs) 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate 1 and 1-monoethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate 2, using tetraethoxysilane as precursor. The addition of water to these ILs resulted in the formation of protonic acid. As a consequence, the ILs functioned as morphology controller and acid pre-catalyst at the same time. Characterization of these materials was performed by photography, scanning electron microscopy, thermogravimetric analysis and powder X-ray diffraction. Compact lamellar monoliths with interlamellar distances of approximately 1.5 nm and flat surfaces were obtained with both ILs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Liquid-liquid interfacial tension of equilibrated mixtures of ionic liquids and hydrocarbons

Ionic liquids are possible alternative solvents for the separation of aromatic and aliphatic hydrocarbons by liquid-liquid extrac- tion. Interfacial tension is an important property to consider in the design of liquid-liquid extraction processes. In this work, the liquid-liquid interfacial tension and the mutual solubility at 25 °C have been measured for a series of biphasic, equilibrated mixtures of an ionic liquid and a hydrocarbon. In particular, the ionic liquids 1-alkyl-3-methylimidazolium bis(trifluorome- thanesulfonyl)imide (with the alkyl substituent being ethyl, hexyl or decyl), 1-ethyl-3-methylimidazolium ethylsulfate, and 1-ethyl-3-methylimidazolium methanesulfonate have been selected, as well as the hydrocarbons benzene, hexane, ethylben- zene, and octane. The selected sets of ionic liquids and hydrocarbons allow the analysis of the influence of a series of effects on the interfacial tension. For example, the interfacial tension decreases with an increase in the length of the alkyl substituent chain of the cation or with an increase of the degree of charge delocalisation in the anion of the ionic liquid. Also, the interfa- cial tension with the aromatic hydrocarbons is markedly lower than that with the aliphatic hydrocarbons. A smaller effect is caused by variation of the size of the hydrocarbon. Some of the observed trends can be explained from the mutual solubility of the hydrocarbon and the ionic liquid.     

Iridium-catalyzed regiospecific allylation of dimethyl malonate in ionic liquids

Allylation of dimethyl malonate with 1-(4-chlorophenyl)prop-2-enyl methyl carbonate in the presence of [Pd(All)Cl]₂, [Rh(COD)Cl]₂, [Ir(COD)Cl]₂ (COD is cycloocta-1,5-diene), and a chiral ferrocenyl-containing phosphite ligand based on (R)-BINOL (BINOL is 2,2′-dihydroxy-1,1′-binaphthyl) in CH₂Cl₂ gave a mixture of linear and branched cross-coupling products, the latter having a moderate optical purity (below 51%). The rhodium-and iridium-catalyzed reactions were very highly regioselective (regiospecific in the case of Ir), giving a branched product. In ionic liquids ([bmim][BF₄] and [bdmim][BF₄]) (bmim is 1-butyl-3-methylimidazolium and bdmim is 1-butyl-2,3-dimethylimidazolium), the Ir-catalyzed reaction regiospecifically afforded a branched product as a racemate. The same result was obtained with [Ir(COD)Cl]₂ as a catalyst; this reaction easily occurred in ionic liquids even without a base. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 519–521, March, 2007.     

Temperature Dependence of Physical Properties of Imidazolium Based Ionic Liquids: Internal Pressure and Molar Refraction

Density, speed of sound and refractive index of the imidazolium-based ionic liquids (ILs), 1-methyl-3-octylimidazolium chloride [C₈mim][Cl], 1-butyl-3-methylimidazolium methyl sulfate [C₄mim][C₁OSO₃], and 1-butyl-3-methylimidazolium octyl sulfate [C₄mim][C₈OSO₃], have been measured in the temperature range from 283.15 to 343.15 K. Experimental density and speed of sound have been used to calculate the internal pressure p _i of the ILs. The p _i values were found to be higher than those of water and molecular organic liquids, but lower than those of classical molten salts. We also calculated molar refraction R _M from the measured refractive index n _D in the temperature range from 288.15 to 343.15 K. Refractive indices of ILs were also higher than those of normal organic liquids, but comparable to long-chain hydrocarbon organic solvents. The structure-property correlation of the ILs has been discussed and the results have been compared to our earlier studies (Kumar in J. Solution Chem. 37:203–214, 2008).     

Ionic Liquid Promoted One-Pot Synthesis of Furo[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidine-2,4(1<Emphasis Type="Italic">H</Emphasis>,3<Emphasis Type="Italic">H</Emphasis>)-diones

Summary. The three-component condensation of aldehyde, N,N′-dimethylbarbituric acid and alkyl or aryl isocyanide afforded the corresponding furo[2,3-d]pyrimidine-2,4(1H,3H)-diones in 1-butyl-3-methylimidazolium bromide as an ionic liquid in high yields at room temperature within several minutes.     

Dissolution and forming of cellulose with ionic liquids

The dissolution of cellulose in different ionic liquids will be described as a very recent subject for a direct dissolving process, which was used to prepare regenerated cellulose fibres. The preparation of the dopes was arranged starting from slurry of cellulose in the aqueous ionic liquid by removing the water at elevated temperature, vacuum and high shearing rates. As ionic liquids, the 1-N-Butyl-3-methylimidazolium chloride, the 1-Ethyl-3-methylimidazolium chloride, the 1-N-Butyl-2,3-dimethylimidazolium chloride, the 1-N-Butyl-3-methylimidazolium acetate and the 1-Ethyl-3-methylimidazolium acetate were investigated. The cellulose solutions in ionic liquids were characterised by means of light microscopy, cone-plate rheometry and particle analysis. In addition these results were compared with cellulose solutions in N-methyl-morpholine-N-oxide monohydrate. Finally the cellulose dopes were shaped by a dry-wet spinning process to manufacture cellulose fibres. The properties of the resulted fibre had been determined and will be discussed.     

Densities and refractive indices of imidazolium- and phosphonium-based ionic liquids: Effect of temperature,alkyl chain length,and anion

A systematic study of densities and refractive indices of 17 room temperature ionic liquids is presented at four different temperatures ranging from 293 K to 333 K. The ionic liquids are grouped into four families: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [C_nmim][Ntf₂], ionic liquids (with n = 2, 4, 6, 8, 10, 12, and 14); 1-alkyl-3-methylimidazolium hexafluorophosphate, [C_nmim][PF₆], ionic liquids (with n = 4, 6, 8); ionic liquids based on the trihexyl(tetradecyl)phosphonium cation, [P_{6 6 6 14}], combined with the anions bis(trifluoromethylsulfonyl)amide, [Ntf₂], acetate, [OAc], and triflate, [OTf]; and [C₄mim]-based ionic liquids combined with the anions [OAc], [OTf], methylsulfate [MeSO₄], and tetrafluoroborate [BF₄]. The data obtained were analysed to determine the effect of (i) temperature, (ii) the alkyl chain length of the 1-alkyl-3-methylimidazolium cation, and (iii) the nature of the anion. Different empirical models for the calculation of the densities of the ionic liquids were tested. Molar refractions were also calculated from the volumetric and refractive index data and the values were discussed with the aim of checking their utility in obtaining insights on the intermolecular forces and behaviour in solution of the different ionic liquids.     

Effects of ionic liquid as additive and the pH of the mobile phase on the retention factors of amino benzoic acids in RP-HPLC

As an organic salt, ionic liquids are widely used as new solvent media. In this paper, three positional isomers, such as o-amino benzoic acid, m-amino benzoic acid, and p-amino benzoic acid are separated with four different ionic liquids as additives to the mobile phase using reversed-phase (RP) high-performance liquid chromatography (HPLC). Amino benzoic acids are biologically active substances; the p-isomer is present in a group of water-soluble vitamins and is widely known as a sunscreen agent. The ionic liquids used are 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium methylsulfate, and 1-octyl-3-methylimidazolium methylsulfate. The effects of the length of the alkyl group on the imidazolium ring and its counterion, the concentrations of the ionic liquid, and the effect of the pH of the mobile phase on the retention factor of the amino benzoic acid isomers are studied. Separation with the ionic liquid in the eluent was better than the separation without the ionic liquid. The pH mainly affected the retention and elution order of the solutes in RP-HPLC.     

Estimates of Internal Pressure and Molar Refraction of Imidazolium Based Ionic Liquids as a Function of Temperature

Estimates of the internal pressure (∂ U/∂ V) _T of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄], 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆], and 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM][BF₄] were made from experimentally determined densities and speeds of sound in the temperature range 283.15 to 343.15 K. Values (∂ U/∂ V) _T for all the ILs studied are higher than those of water and molecular organic liquids. We also measured the refractive indices n _D in the temperature range 288.15 to 343.15 K and estimated the molar refraction R _M. Refractive indices of ILs were also higher than those of normal organic liquids but were comparable to those of long hydrocarbon chain organic solvents.     

Homogeneous tritylation of cellulose in 1-butyl-3-methylimidazolium chloride

1-Alkyl-3-methylimidazolium-based ionic liquids, having chloride as a counter ion, were studied for cellulose solubility; and the influence of different alkyl chain lengths was also investigated. The alkyl chain length was incrementally varied from ethyl to decyl to determine structure-dissolution properties; a distinct odd-even effect was observed for short chain lengths. In addition, the tritylation of cellulose was performed in 1-butyl-3-methylimidazolium chloride using pyridine as base. The influences of reaction time and the ratio of trityl chloride per cellulose monomer unit on the degree of substitution were investigated in detail by elemental analysis and 1H NMR spectroscopy. A DS of around 1 was obtained after 3 h reaction time using a six fold excess of trityl chloride.