Common Ionic Liquids Research Articles

Effective Hydrolysis of Cellulose into Glucose over Sulfonated Sugar-Derived Carbon in an Ionic Liquid

Sulfonated sucrose-derived carbon, glucose-derived carbon, and nut shell activated carbon (NSAC) catalysts were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). FT-IR and XPS spectra showed that −SO3H groups could be introduced into the carbon precursors after the sulfonation treatment. Higher concentration of −SO3H groups in the sulfonated sucrose-carbon and glucose-carbon most likely accounts for their higher activities compared to sulfonated NSAC. Hydrolysis of microcrystalline cellulose was examined in a common ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), with the sulfonated carbon catalysts. Maximum yields of glucose (59%) and total products (80%, defined as the sum of glucose, cellobiose, and 5-hydroxymethylfurfural) could be obtained with sulfonated sucrose-carbon at 120 °C for 4 h. With a regeneration procedure, the catalyst could be reused.

Ionic liquids behave as dilute electrolyte solutions

We combine direct surface force measurements with thermodynamic arguments to demonstrate that pure ionic liquids are expected to behave as dilute weak electrolyte solutions, with typical effective dissociated ion concentrations of less than 0.1% at room temperature. We performed equilibrium force-distance measurements across the common ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][NTf2]) using a surface forces apparatus with in situ electrochemical control and quantitatively modeled these measurements using the van der Waals and electrostatic double-layer forces of the Derjaguin-Landau-Verwey-Overbeek theory with an additive repulsive steric (entropic) ion-surface binding force. Our results indicate that ionic liquids screen charged surfaces through the formation of both bound (Stern) and diffuse electric double layers, where the diffuse double layer is comprised of effectively dissociated ionic liquid ions. Additionally, we used the energetics of thermally dissociating ions in a dielectric medium to quantitatively predict the equilibrium for the effective dissociation reaction of [C4mim][NTf2] ions, in excellent agreement with the measured Debye length. Our results clearly demonstrate that, outside of the bound double layer, most of the ions in [C4mim][NTf2] are not effectively dissociated and thus do not contribute to electrostatic screening. We also provide a general, molecular-scale framework for designing ionic liquids with significantly increased dissociated charge densities via judiciously balancing ion pair interactions with bulk dielectric properties. Our results clear up several inconsistencies that have hampered scientific progress in this important area and guide the rational design of unique, high-free-ion density ionic liquids and ionic liquid blends.

Conductivity and Solvation Dynamics in Ionic Liquids.

It was shown recently that a simple dielectric continuum model predicts the integral solvation time of a dipolar solute ⟨τsolv⟩ to be inversely proportional to the electrical conductivity σ0 of an ionic solvent or solution. In this Letter, we provide a more general derivation of this connection and show that available data on coumarin 153 (C153) in ionic liquids generally support this prediction. The relationship between solvation time and conductivity can be expressed by ln(⟨τsolv⟩/ps) = 4.37 - 0.92 ln (σ0/S m(-1)) in 34 common ionic liquids.

A simple correlation to predict high pressure solubility of carbon dioxide in 27 commonly used ionic liquids

Engineers often demand the availability of easy correlations without difficult and time-consuming calculations. Up till now, there has been a lack of such correlations for mixtures of CO2+ionic liquids. This work proposes a correlation to predict CO2 solubility in 27 common ionic liquids. The main advantages are its simplicity and minimal input data, namely temperature and pressure. The ionic liquids investigated ranged within a variety of families, having various anions and cations. Compared with the popular engineering models of Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK), the present correlation is much easier to use, yet it is also more accurate (PR, SRK and the proposed model had AARD% values of 43.5%, 44.3% and 4.9%, respectively for a total of 3073 data), even when binary interaction coefficients of PR and SRK are optimized to experimental data (AARD% values of 17.2%, 16.9% and 4.9% for PR, SRK and the proposed model, respectively).

Differential dynamic potentiometric responses obtained with anion-selective electrodes for perchlorate, thiocyanate, iodide, nitrate, sulfate, picrate and bis(trifluoromethylsulfonyl) imide

Differential dynamic potentiometric (DDP) responses for perchlorate, thiocyanate, iodide, nitrate and sulfate as inorganic anions, and picrate and bis(trifluoromethylsulfonyl) imide, a common ionic liquid anion, as organic anions are presented. DDP signals were obtained as the difference between the individual potential responses displayed by two anion-selective electrodes, one containing a membrane with β-cyclodextrin (β-CD) as anion-ionophore and the other containing a similar membrane without β-CD (blank membrane). Highly reproducible DDP signals characteristic for each anion were obtained. Principal components (PC) analysis applied to the DDP responses permitted differentiation of the anions assayed. Additionally, a linear relationship was found between the PC1 values of each anion signal and the corresponding values of an anion lipophilicity descriptor. Finally, the DDP technique was extended to the study of some anion mixtures.

Transformations in plasma membranes of cancerous cells and resulting consequences for cation insertion studied with molecular dynamics

Structural and energetic transformations in the plasma membrane of a cancerous cell are investigated together with related consequences for the insertion of small cationic compounds. Molecular dynamics simulations are performed with an empirical force field on two membrane models that represent the membrane of a cancerous cell (M-Cancer) and of a healthy cell (M-Eukar), respectively. An eight-fold increase of negatively charged phosphatidylserine in the external membrane layer as well as a reduction of cholesterol concentration by half is taken into account to describe the membrane transformation. Three additional reference membranes are prepared and consist of pure phosphatidylcholine (M-PC), where 20% is replaced with phosphatidylserine (M-PC0.8S0.2), and where 34% is replaced with cholesterol (M-PC0.66Ch0.34), respectively. Moreover, the free energy released by inserting octadecylmethylimidazolium (OMIM(+)), a cation found in a class of common ionic liquids, into M-Eukar, M-Cancer as well as into the three reference model membranes is derived by applying thermodynamic integration. We find that the presence of serine improves the solvation of the membrane through favorable electrostatic interactions with solvated sodium ions, where a significant number of sodium ions are capable of penetrating the upper polar layer of the membrane. However, the insertion free energy of OMIM(+) does not seem to be influenced by serine in the membrane. Furthermore, a significant serine induced structural reorganization of the membrane is not observed. In contrast, a reduction of cholesterol in the membrane models leads to smaller lipid surface densities, thinner membranes as well as less ordered and less stretched lipids as expected. We also observe that cholesterol reduction leads to a rougher membrane surface and an increased solvent accessibility of the hydrophobic membrane core. Membrane insertion of OMIM(+) becomes significantly more favorable in the absence of cholesterol, with an increased insertion free energy release of 7.1 kJ mol(-1) in M-Cancer compared to M-Eukar. Overall, the results suggest only a minor influence of serine on membrane organization but do not rule out an influence on cation insertion through a stronger cation adsorption to the membrane surface. In contrast, cholesterol seems to impede OMIM(+) insertion by increasing the density of polar lipids on the membrane surface and by flattening the membrane surface. These observations are shedding some light on the previously observed selective disruption of cancerous cells induced by cationic compounds such as found in ionic liquids.

Reclamation and reuse of ionic liquids from silica-based ionogels using spontaneous water-driven separation

Ionic liquids (ILs) are widely regarded as “green” materials, partially because they are assumed to be recyclable in most applications. Here, the effectiveness of a water-based IL reclamation process with low energy requirements is demonstrated using two types of silica-supported ionic liquid-based gel electrolytes (ionogels) incorporating a variety of common ionic liquids. More than 90% of the IL can be separated from the ionogel silica scaffold simply by submerging the ionogel in water, with no additional energy input. It is posited that water is able to compete with the hydrophobic IL for access to the hydrophilic silica scaffold surface, liberating the IL from the ionogel structure. Spontaneous water-based separation leads to the recovery of at least 70% of the original IL mass; transfer losses experienced at the laboratory scale are expected to decrease with process scale-up. Recovered ILs exhibit similar electrical performance to the virgin materials in a double layer capacitor structure.

Effect of Ionic Liquid Impurities on the Synthesis of Silver Nanoparticles

Imidazolium-based ionic liquids have been widely utilized as versatile solvents for metal nanoparticle synthesis; however, reactions to synthesize silver nanoparticles that are performed identically in different commercially obtained lots of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF(4)) give divergent results. This suggests that impurities in these nominally identical solvents play an important role in the resulting silver nanoparticle quality. To test the effect that impurities have on the quality of silver nanoparticles synthesized in BMIM-BF(4), silver nanoparticles were synthesized in carefully prepared and purified BMIM-BF(4) and compared against silver nanoparticles that were synthesized in the purified BMIM-BF(4) that had been spiked with trace amounts of water, chloride, and 1-methylimidazole. It was clearly demonstrated that trace amounts of these common ionic liquid impurities cause significant deviation in size and shape (creating polydisperse and irregularly shaped ensembles of both large and small particles), and also negatively impact the stabilization of the resulting silver nanoparticles.

Probing Solvation in Ionic Liquids via the Electrochemistry of the DPPH Radical

The electrochemistry of the radical species 2,2-diphenyl-1-picrylhydrazyl, DPPH, has been studied in a range of common ionic liquids and its voltammetric response found to vary with the choice of anion. The trend observed is used to provide a relative Lewis basicity scale of nine ionic liquids commonly used as solvents.

Bilayer Membrane Permeability of Ionic Liquid-Filled Block Copolymer Vesicles in Aqueous Solution

The bilayer membrane permeability of block copolymer vesicles ("polymersomes") with ionic liquid interiors dispersed in water is quantified using fluorescence quenching. Poly((1,2-butadiene)-b-ethylene oxide) (PB-PEO) block copolymer vesicles in water with their interiors filled with a common hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, were prepared containing a hydrophobic dye, Nile Red, by intact migration of dye-encapsulated vesicles from the ionic liquid to water at room temperature. A small quencher molecule, dichloroacetamide, was added to the aqueous solution of the dye-loaded vesicles, and the permeation of the quencher passing through the membrane into the interior was determined from the fluorescence quenching kinetics. Rapid permeation of the quencher across the nanoscale membrane was observed, consistent with the high fluidity of the liquid polybutadiene membrane. Two different PB-PEO copolymers were employed, in order to vary the thickness of the solvophobic membrane. A significant increase in membrane permeability was also observed with decreasing membrane thickness, which is tentatively attributable to differences in quencher solubility in the membranes. Quantitative migration of the vesicles from the aqueous phase back to an ionic liquid phase was achieved upon heating. These microscopically heterogeneous and thermoresponsive vesicles with permeable and robust membranes have potential as recyclable nanoreactors, in which the high viscosity and capital expense of an ionic liquid reaction medium can be mitigated, while retaining the desirable features of ionic liquids as reaction media, and facile catalyst recovery.

ChemInform Abstract: Synthesis of Ionic Liquids Containing the Hydroxyl Functionality for Extracting Nonylphenol and Octylphenol in Water.

AbstractNew ionic liquids containing the hydroxyl functionality (I) and (II) show much better extraction efficiencies for nonyl‐ and octylphenol than the common ionic liquids, such as [bmim]PF6.

A novel electrochemical biosensing platform based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composites

A commercially available aqueous poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) as the immobilization matrix of biologically active species for the development of sensing and biosensing devices has not been widely reported due to its swelling and disintegration in aqueous solution. In this paper, a lowly swelling and disintegrating PEDOT:PSS composite films as the electrochemical biosensing platform was successfully developed by the incorporation of the biocompatible binding agent and common ionic liquid. Nafion was selected as a binding agent, mainly because Nafion could provide the biocompatible environment for biologically active species, improve the adhesion and binding force between films and electrode interface, and prevent peeling off of both enzyme molecules and films. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of common ionic liquids, was used for the secondary dopant and enhancer to improve the water-resistance and electrochemical properties of PEDOT:PSS films. Ascorbate oxidase was used as a mode for the development and application of the electrochemical biosensor. The prepared PEDOT:PSS composite modified electrode exhibited the pronounced water-stability. Moreover, the fabricated biosensor displayed an excellent bioelectrocatalytic activity to the oxidation of vitamin C, fast current response, high sensitivity, wide linear range, low detection limit, high bioaffinity and specificity, and satisfactory results in practical application, indicating that the fabricated biosensor has good electrochemical biosensing performance. Meanwhile, the excellent water-stability, repeatability, reproducibility, storage stability, and electrochemical biosensing performance also make PEDOT:PSS composite modified matrix an interesting candidate for the sensing and biosensing application in the near future.

Tribological properties of halogen-free ionic liquids

The tribological properties of halogen-free ionic liquids, tricyanomethanide [[Formula: see text]] salt, tetracyanoborate [[Formula: see text]] salts, and N-alkylimidazole-trialkylborane complexes were evaluated by laboratory tribo-testing of steel–steel contact under boundary conditions. Tricyanomethanide salt is composed of hydrogen, carbon, and nitrogen. The other two types of liquids are composed of hydrogen, boron, carbon, and nitrogen. They are free of halogens and heavier elements that are components of common ionic liquids, such as fluorine, phosphorus, and sulphur. As expected, the halogen-free ionic liquids exhibited low corrosion properties to steel. When evaluated as neat liquid, these halogen-free ionic liquids provided less tribological properties in comparison with a reference, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. Tributylmethylphosphonium dimethylphosphate was examined as a prototype tribo-improving additive. It improved the wear-preventing properties and friction reducing properties of tetracyanoborate salts by 10–25% and 20–30% at a concentration of 10 mM (620 ppm of phosphorus), respectively. The additive performances for tricyanomethanide salt and the imidazole-trialkylborane complexes were not uniform under these conditions. Boron oxide and iron oxides were found by surface analysis of rubbed surfaces with tetracyanoborate salts.

Redox Properties of a Rhenium Tetrazolato Complex in Room Temperature Ionic Liquids: Assessing the Applicability of the Stokes–Einstein Equation for a Metal Complex in Ionic Liquids

The redox properties of a rhenium-tetrazolato complex, namely fac-[Re(CO)3(phen)L] (where L is 5-(4′-cyanophenyl)tetrazolate), have been studied by cyclic voltammetry in a range of common room temperature ionic liquids (RTILs) with different anions and cations. In all eight RTILs, one reduction and two oxidation peaks are observed. It is believed that the reduction peak corresponds to ligand reduction and the two oxidation peaks are two one-electron oxidations of the metal from Re(I) to Re(II) and Re(II) to Re(III). The redox potentials of the metal oxidations appear to be unchanged with the solvent; however, the potential for the reduction peak is more negative in RTILs containing the [P14,6,6,6]+ cation, suggesting a stabilization effect of the electrogenerated intermediate with the other RTIL cations studied (imidazolium and pyrrolidinium). Potential step chronoamperometric experiments were used to calculate diffusion coefficients of the complex in RTILs, and it was found that fac-[Re(CO)3(phen)L] diffuses very slowly through the RTIL medium. A plot of diffusion coefficient against the inverse of viscosity of the RTIL solvent showed a linear trend, suggesting that the Stokes–Einstein relationship generally applies for this complex in RTILs, but the coefficient on the denominator is likely to be closer to 4 (the “slip” limit) than 6 (the “stick” limit) when taking into account the hydrodynamic radius.

Efficient synthesis of phytosteryl esters using the Lewis acidic ionic liquid

Phytosteryl esters are of significant importance due to their recent recognition and contribution as cholesterol-lowering agents in food and nutrition. The synthesis of phytosteryl esters from phytosterols and fatty acids in the presence of ionic liquids with high yield and purity was investigated. Six common ionic liquids, including [Bmim]BF4, [Bmim]CF3SO3, ChCl·2SnCl2, ChCl·2ZnCl2, ChCl·2.5SnCl2 and ChCl·2FeCl3, were evaluated to determine the satisfactory catalyst for the esterification, and the results showed that ChCl·2SnCl2 was the most suitable catalyst in this study. Moreover, it was found that the catalytic activity of ionic liquids for the esterification enhanced with the increase of their Lewis acidity, which was determined by pyridine as IR spectroscopic probe. The reaction conditions were further surveyed and the experimental esterification rate reached a greatly high level of 92.3% using ChCl·2SnCl2 as catalyst with the molar ratio 3:1 (lauric acid:plant sterols) at 150°C for 4h. FT-IR, MS, and NMR analyses were adopted to evaluate the synthesized phytosteryl laurate. And also the physiochemical property of phytosterols and phytosteryl laurate was compared, suggesting that phytosteryl ester favored its wide application in fatty based food.

Anionic Surfactant Ionic Liquids with 1-Butyl-3-methyl-imidazolium Cations: Characterization and Application

For the first time a series of anionic surfactant ionic liquids (SAILs) has been synthesized based on organic surfactant anions and 1-butyl-3-methyl-imidazolium cations. These compounds are more environmentally friendly and chemically tunable as compared to other common ionic liquids. A detailed investigation of physicochemical properties highlights potential applications from battery design to reaction control, and studies into aqueous aggregation behavior, as well as structuring in pure ILs, point to possible uses in electrochemistry.

Hydrolysis study of fluoroorganic and cyano-based ionic liquid anions – consequences for operational safety and environmental stability

The hydrolytic stability of ionic liquid anions is a key property with regard to their technical applicability and environmental stability. From a technical point of view hydrolytic processes may lead to reduced durability, diminished technical performance and reduced operational safety in that corrosive and/or toxic hydrolysis products are formed. On the other hand, susceptibility to hydrolytic processes is advantageous where environmental stability and persistency are concerned, since hydrolysis is the most important abiotic degradation pathway in the environment. We investigated the hydrolytic stability of the most common ionic liquid anions, dicyanimide [N(CN)2]−, tricyanmethanide [C(CN)3]−, tetracyanidoboranate [B(CN)4]−, bis(trifluoromethylsulphonyl)imide [(CF3SO2)2N]−, trifluorotris(pentafluoroethyl)phosphate [(C2F5)3PF3]− and 1,1,2,2-tetrafluoroethanesulphonic acid [H(C2F4)SO3]−, as a function of pH (1, 7, 9 and 13) and temperature. The results show that there was no difference in hydrolytic stability as recorded for 1-ethyl-3-methylimidazolium (IM12) or for the alkali cations. All the anions were stable under neutral and slightly basic conditions (half-lives at 25 °C ⇒1 year). In strongly acidic and basic solutions, however, B(CN)4−, (CF3SO2)2N−, (C2F5)3PF3− and H(C2F4)SO3− were hydrolytically stable, whereas N(CN)2− and C(CN)3− were not. The kinetics of hydrolysis were recorded and Arrhenius plots were generated for the latter two anions. In addition, their hydrolysis pathways and the resulting products were identified via mass spectrometry. The cytotoxicity of hydrolysed IL solutions towards the mammalian cell line IPC-81 and the identified hydrolysis products (pure compounds) was investigated for a first estimate of their toxicological properties.

(Eco)toxicity of fluoro-organic and cyano-based ionic liquid anions

The (eco)toxicity of the most common ionic liquid anions like [N(CN)(2)](-), [C(CN)(3)](-), [B(CN)(4)](-), [(CF(3)SO(2))(2)N](-), [(C(2)F(5))(3)PF(3)](-) was investigated in test systems of different trophic level. In the same order, and thus with increasing hydrophobicity, a trend of higher toxicity was found. Especially the [(C(2)F(5))(3)PF(3)](-) moiety poses a significant hazard towards aquatic organisms.

Chemisorption of carbon dioxide in imidazolium based ionic liquids with carboxylic anions

The absorption ability of carbon dioxide in ionic liquids (IL) containing a basic anion like acetate was investigated and compared to common ionic liquids as well as nitrogen data. Thereby, the IL showed chemisorption due to a formation of carboxylate at the imidazolium ring. The results obtained from [EMIM] [pivalate] are promising, since the IL could be completely recovered with a simple evacuating step, and without further heating, while having a similar absorption ability than [EMIM] [OAc].From the temperature dependency of the carbon dioxide absorption in [EMIM] [OAc] it can be seen that the solvation enthalpy is much smaller compared to common ionic liquids with physical absorption.Furthermore, the addition of the superbase DBU to [EMIM] [OAc] increased the CO2-loading capacity.

ChemInform Abstract: Microwave Assisted Suzuki Reaction in N‐Butylpyridinium Salts/Water Systems.

AbstractIt is demonstrated that an ionic liquid derived from 4‐picoline is an efficient medium.