Methylimidazolium-based Ionic Liquids Research Articles

Evaluation of inhibition performance of methylimidazolium ionic liquids on surface of mild steel in sulfuric acid

In the present study, the microwave irradiation approach was used to synthesize two methylimidazolium-based ionic liquids (MImILs), specifically 1-Heptyl-3-methylimidazolium bromide [HMImBr] and 1-Benzyl-3-methylimidazolium bromide [BzMImBr]. Several spectroscopic methods have been used to characterize the produced compounds. Gravimetric and electrochemical techniques were employed to examine their ability to prevent corrosion of the mild steel in a 0.5 M sulfuric acid solution. Amongst all the evaluated ionic liquids, [BzMImBr] having an aromatic ring instead of hexyl ((–CH2)5–CH3) hydrocarbon of [HMImBr] manifests better inhibition efficiency of 95.49 % at 1000 ppm concentration. The experimental ionic liquids negatively impact both the anodic and cathodic Tafel reactions, exhibiting mixed-type inhibition properties, as demonstrated by the findings of the potentiodynamic polarization investigations. Through their adsorption employing their electron-rich centres, the examined ionic liquids create a corrosion-protective covering, and their adsorption follows the Langmuir isotherm model. Negative values of ΔGads indicate the spontaneous nature of [HMImBr] and [BzMImBr] adsorption, whereas values between −20 and −40 KJ mol−1 indicate the physio-chemisorption mode of adsorption. Energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and field emission-scanning electron microscopy (FE-SEM) techniques were used to assess and evaluate surface morphology. The DFT-based analysis indicates that aromatic rings played a significant role in the charge sharing (donation and acceptance) in [BzMImBr].

Ionic Liquid Assisted Exothermic Complexation of Trivalent Lanthanides with Fluorinated β Diketone: Multitechnique Approach with Theoretical Insight.

The complexation of the betadiketone,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (HFOD) was studied with trivalent lanthanide ions, viz. Nd3+, La3+, and Eu3+ in several methylimidazolium-based ionic liquids (Cnmim•NTf2, where, n = 4,6,8). In C6mim•NTf2, predominant formation of ML2+ and ML4- species was evidenced from the UV-vis absorption (Nd3+) as well as luminescence (Eu3+) spectral studies with log β2 ≈ 5.88 ± 0.04, log β4 ≈ 10.95 ± 0.06. The formation constants followed the trend C4mim•NTf2 > C6mim•NTf2 > C8mim•NTf2. The asymmetry factors for the ML2+ and ML4- species were found to be 1.2 and 1.59, respectively. The ML4- complex was found to have one primary coordination sphere water molecule with enhanced covalency between Eu3+ and O from HFOD (Judd Offelt constants Ω2 and Ω4 ≈ 17.2 and 2.35) compared to Eu3+aq, yet comparable to other β diketones. Complexation-induced temperature increase was confirmed by calorimetric measurements, indicating the exothermic complexation reaction (ΔHcomplexation ≈ -13.7 kJ mol-1), which is also spontaneous in nature (ΔG ≈ -68.1 kJ mol-1), with an enhancement in the entropy values. Due to complexation, the shifts in the peak positions (1686.66 cm-1, 1633.53 cm-1) associated with β diketone/ketone functional groups were evidenced. Density functional theory (DFT) calculation was performed to optimize the structural parameters including bond distance, bond angles, and energetics associated with the complexation.

The Role of the Anion in Imidazolium-Based Ionic Liquids for Fuel and Terpenes Processing.

The potentialities of methylimidazolium-based ionic liquids (ILs) as solvents were evaluated for some relevant separation problems-terpene fractionation and fuel processing-studying selectivities, capacities, and solvent performance indices. The activity coefficients at infinite dilution of the solute (1) in the IL (3), γ13∞, of 52 organic solutes were measured by inverse gas chromatography over a temperature range of 333.2-453.2 K. The selected ILs are 1-butyl-3-methylimidazolium hexafluorophosphate, [C4mim][PF6], and the equimolar mixture of [C4mim][PF6] and 1-butyl-3-methylimidazolium chloride, [C4mim]Cl. Generally, low polar solutes follow γ1,C4mimCl∞ > γ1,C4mimPF6+C4mimCl∞ > γ1,C4mimPF6∞ while the opposite behavior is observed for alcohols and water. For citrus essential oil deterpenation, the results suggest that cations with long alkyl chains, such as C12mim+, promote capacity, while selectivity depends on the solute polarity. Promising results were obtained for the separation of several model mixtures relevant to fuel industries using the equimolar mixture of [C4mim][PF6] and [C4mim]Cl. This work demonstrates the importance of tailoring the polarity of the solvents, suggesting the use of ILs with mixed anions as alternative solvents for the removal of aliphatic hydrocarbons and contaminants from fuels.

Solubility of carbon dioxide in promising methylimidazolium-based ionic liquids

One of the most pressing environmental concerns facing humanity today is the limitation of carbon dioxide emissions. In the field of natural gas sweetening, carbon capture is equally critical. CO2 solubility in three promising ionic liquids {1-Hexyl-3-methylimidazolium bis(trifluoro-methyl-sulfonyl) imide [HMIM][Tf2N], 1-Butyl-3-methylimidazolium dimethyl-phosphate [BMIM][DMP], and 1-Propyl-3-methylimidazolium (trifluoromethylsulfonyl)imide [PMIM][Tf2N]} was measured at (303.15, 323.15 and 343.15) K and pressures up to 1.4 MPa. The densities of the three ionic liquids were determined at atmospheric pressure (98.5 ± 0.8 kPa) and temperatures ranging from (293.15 to 343.15) K.The lowest Henry's Law constant (highest capacity) for CO2 was that of [HMIM][Tf2N] followed by [PMIM][Tf2N] and [BMIM][DMP]. [HMIM][Tf2N] also had a higher absorption capacity than Selexol/Genesorb 1753 and was second best only to 1-Octyl-3-methylimidazolium bis (trifluoro-methane sulfonyl) imide [OMIM][Tf2N] among all ionic liquids, based on solubility data published in the literature. Note that [BMIM][DMP] was also found to be among the best four ionic liquids according to the Henry's Law data collected from the literature.Three distinct mixing rules were used to correlate the experimental CO2 solubility data with the Peng-Robinson equation of state (PR-EoS) using the van der Waals one (vdW1), van der Waals two (vdW2), and the Wong-Sandler mixing rule along with the Non-Random Two-Liquid model (WS-NRTL). The average absolute deviations for vdW1, vdW2, and WS-NRTL mixing rules, when calculated for the three ionic liquid systems at the three temperatures, were 4.89 %, 0.82 %, and 0.84 %, respectively.

Ionic liquid derived novel deep eutectic solvents as low viscous electrolytes for energy storage

This work investigates a newly emerging class of solvents to be used as alternatives to or complementarily with ionic liquid (IL) electrolytes. Three novel deep eutectic solvents (DESs) comprised of the hydrogen bond donors (HBDs), namely N-Methylacetamide (NMAc) and formamide, were formulated with three variants of the methyl imidazolium-based ionic liquids (ILs) as hydrogen bond acceptors (HBAs). ILs consisting of 1-butyl-3-methyl imidazolium ([BMIM]) cation with anions namely methanesulphonate ([MeSO3]), bis(trifluoromethylsulfonyl)imide ([Tf2N]), and hexafluorophosphate ([PF6]) were used as hydrogen bond acceptors. Initially, the eutectic points of the DESs were estimated using a quantum chemical-based thermodynamic model, namely Conductor like Screening Model-Segment Activity Coefficient (COSMO-SAC). The calculated melting points of the DESs were determined to be markedly lower than those of both the constituent components. Further, physical and chemical characterization was done on the synthesized DESs. The viscosities (<20 cp) were found to be significantly lower than those of conventionally used pure room temperature ILs, and ionic conductivities (>5 mS/cm) were found to be appreciably higher than those of the corresponding constituent ILs. Thermogravimetric analysis revealed negligible mass loss up to 80–100 °C. Linear scan voltammetry (LSV) was employed to determine the electrochemical stable potential window (ESPW) of the solvents with a glassy carbon (GC) electrode. LSV provided electrochemical stabilities in the range of 3.8–4 V for all three studied deep eutectic solvents, comparable to pure ILs and far higher than the potential windows of mixtures of ILs and organic solvents, a blend commonly used as electrolytes.

Solubility of Carbon Dioxide in Promising Methylimidazolium-Based Ionic Liquids

Solubility of Carbon Dioxide in Promising Methylimidazolium-Based Ionic Liquids

Ionic liquids as entrainers for terpenes fractionation and other relevant separation problems

This work discusses the potential of two phosphonium-based ionic liquids (ILs), [P6,6,6,14]Cl and [P6,6,6,14][(C8H17)2PO2], and one methylimidazolium-based IL, [C4mim][OAc], as entrainers in the fractionation of terpene mixtures, in the desulfurization and denitrification of fuel oils, and in the separation of aromatics from aliphatic hydrocarbons. To this aim, the activity coefficients at infinite dilution of 45 solutes were obtained by gas-chromatography in the temperature range (333.15–458.15) K. Selectivities and capacities were calculated showing that [P6,6,6,14]Cl is adequate for the fractionation of (−)-menthone/L-(−)-menthol mixture, being also a suitable option for the deterpenation of citrus essential oil, and the removal of thiophene and pyridine from aliphatic hydrocarbons. To complement the experimental measurements COSMO-RS model was tested, demonstrating good potential to screen separation agents and give insights for several important separation problems, including the removal of contaminants from fuels and the isolation, fractionation and purification of terpenes mixtures.

Systematic Study of Ionic Liquids Based Coal Extraction: Selectivity in Extract Molecular Weights and Targeted Functional Groups

Ionic liquids (ILs) are environmentally friendly solvents that have been used to extract valuable compounds from coal and biomass. In this work, eight methylimidazolium-based ionic liquids were sel...

Alkyl Methyl Imidazolium-Based Ionic Liquids at the Au(111) Surface: Anions and Alkyl Chain Cations Induced Interfacial Effects

The structure, stability, and adsorption mechanism on the Au(111) surface of hydrophilic/hydrophobic ionic liquids (ILs) with various lengths of the alkyl chain group in the cation were investigate...

Methylimidazolium-based ionic liquids influence the biobutanol production by solvent-producing Clostridium

Ionic liquids (ILs) used to pretreat lignocellulosic biomass could stimulate or be detrimental to the subsequent fermentation process when the ILs retained in the biomass hydrolysate. This study aimed to investigate if the presence of the ILs including 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-ethyl-3-methylimidazolium chloride ([EMIM][Cl]), 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), and1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]) either enhanced or inhibited biobutanol production by Clostridium saccharoperbutylacetonicum N1-4. Results show that the presence of the five ILs at low concentration increased the butanol productions. The maximum butanol concentrations were obtained at 1 g L−1 for [AMIM][Cl], [BMIM][Cl], [EMIM][Cl], and [EMIM][DEP], and at 0.5 g L−1 for [EMIM][Ac]. The increase in the butanol concentrations was advantageous to the butanol and total solvent (acetone, butanol and ethanol) yields. Conversely, the butanol production rates were generally reduced by the ILs except for the observed hormesis at 0.5 and 1.0 g L−1 of both [BMIM][Cl] and [EMIM][Cl]. It was also observed that high levels of ILs impeded the speed of cell growth and thus decelerated the butanol production. Overall, the acetone-butanol-ethanol (ABE) fermentation was stimulated at low IL concentrations whereas was hindered at high concentrations.

Electrochemical Stability Window of Imidazolium-Based Ionic Liquids as Electrolytes for Lithium Batteries.

This paper presents the computational assessment of the electrochemical stability of a series of alkyl methylimidazolium-based ionic liquids for their use as lithium battery electrolytes. The oxidation and reduction potentials of the constituent cation and anion of each ionic liquid with respect to a Li(+)/Li reference electrode were calculated using density functional theory following the method of thermodynamic cycles, and the electrochemical stability windows (ESW)s of these ionic liquids were obtained. The effect of varying the length of alkyl side chains of the methylimidazolium-based cations on the redox potentials and ESWs was investigated. The results show that the limits of the ESWs of these methylimidazolium-based ionic liquids are defined by the oxidation potential of the anions and the reduction potential of alkyl-methylimidazolium cations. Moreover, ionic liquids with [PF6](-) anion have a wider ESW. In addition to characterizing structure-function relationships, the accuracy of the computational approach was assessed through comparisons of the data against experimental measurements of ESWs. The potentials calculated by the thermodynamic cycle method are in good agreement with the experimental data while the HOMO/LUMO method overestimates the redox potentials. This work demonstrates that these approaches can provide guidance in selecting ionic liquid electrolytes when designing high-voltage rechargeable batteries.

Effect of methylimidazolium-based ionic liquids on vapor–liquid equilibrium behavior of tert-butyl alcohol + water azeotropic mixture at 101.3 kPa

Three ionic liquids (ILs), 1-ethyl-3-methylimidazolium bromine ([EMIM]Br), 1-butyl-3-methylimidazolium bromine ([BMIM]Br), and 1-hexyl-3-methylimidazolium bromine ([HMIM]Br), were used as the solvent for separation of {tert-butyl alcohol (TBA)+water} azeotrope. Vapor–liquid equilibrium (VLE) data for {TBA+water+IL} ternary systems were measured at 101.3kPa. The results indicate that all the three ILs produce an obvious effect on the VLE behavior of {TBA+water} system and eliminate the azeotropy in the whole concentration range. [EMIM]Br is the best solvent for the separation of {TBA+water} system by extractive distillation among the three ILs. The experimental VLE data for the ternary systems are correlated with the NRTL model equation with good correlations. Explanations are given with activity coefficients of water and TBA, and the experimental VLE-temperature data for {TBA or water+IL} binary systems.

Influence of Chemical Structure on the Solubility of Low Molecular Weight Carbohydrates in Room Temperature Ionic Liquids

The use of room temperature ionic liquids (ILs) as green solvents is an emerging and innovative technology, which is quickly expanding in carbohydrate chemistry. However, information about solubility of low molecular weight carbohydrates (LMWC) in ILs is still scarce. This study provides new solubility data for several LMWC dissolved in methylimidazolium-based ILs. Different solubility values have been obtained for carbohydrates depending on their structure. In general, ketoses are more soluble than their corresponding aldoses, and trisaccharides are more soluble than mono- and disaccharides, although some exceptions have been observed depending on the tested IL. [BMIM][MeSO4] and [HMIM][Cl] acted both as solvent and as catalyst for dehydration of ketoses (fructose and tagatose) into 5-hydroxymethylfurfural at 318 K. These findings pointed out the potential of ILs as an interesting alternative solvent for new applications in applied carbohydrate chemistry.

First Principle Approach to Solvation by Methylimidazolium-Based Ionic Liquids

Understanding the nature of the inter- and intramolecular interactions of solutes and ionic liquid (IL) ion pairs from an electronic point of view is necessary for explaining the mechanisms behind the selectivity of ILs toward a certain solute. Due to the complexity of the underlying physicochemical interactions, and aiming at a reliable representation of the solute-IL interactions, the model system chosen in this work is formed by one single ion pair and the solute of interest, in the gas phase. Ab initio molecular dynamics (MD) techniques are used for ensuring a complete scan of the potential energy surface. A representative number of structures extracted from this trajectory are optimized using more sophisticated DFT methods. Posterior bond analysis (with natural bonding orbitals (NBO), and Morokuma-like energy partition) provide a detailed picture of the solute-IL bond nature for a set of various solutes, anions, and cations, to find a relationship between the gas phase electronic characteristics and the experimentally observed behavior. The approximation to the ILs solvation properties employing this very basic model shows that, on one side, the specific interaction of the solute with methylimidazolium-based IL is a reliable indication of the overall affinity between the bulk IL and the solute, and can be considered a predictive tool for the bulk behavior. Furthermore, the systematic study carried out has permitted the rational comprehension of such properties and thus permits us to extend it to other systems.

Ionothermal synthesis of uranyl compounds that incorporate imidazole derivatives

Ionothermal reactions of uranyl nitrate with various salts in methylimidazolium-based ionic liquids have produced single crystals of three uranyl compounds that incorporate imidazole derivatives as charge-balancing cations. (C4H7N2)[(UO2)(PO3F)(F)] (1) crystallizes in space group C2, a=17.952(1)Å, b=6.9646(6)Å, c=8.5062(7)Å, β=112.301(1)°, (C6H11N2)2[(UO2)(SO4)2] (2) crystallizes in space group C2/c, a=31.90(1)Å, b=9.383(5)Å, c=13.770(7)Å, β=93.999(7)° and (C6H11N2)[(UO2)2(PO4)(HPO4) (3) crystallizes in space group P21/n, a=9.307(2), b=18.067(4), c=9.765(2), β=93.171(2). The U6+ cations are present as (UO2)2+ uranyl ions coordinated by three O atoms and two F atoms in 1 and five O atoms in 2 and 3 to give pentagonal bipyramids. The structural unit in 1 is composed of F-sharing dimers of uranyl pentagonal bipyramids linked into sheets through corner-sharing fluorophosphate tetrahedra. The structural unit in 2 is composed of uranyl pentagonal bipyramids with one chelating sulfate tetrahedron linked into chains by three other corner-sharing sulfate tetrahedra. In 3, the structural unit is composed of chains of uranyl pentagonal bipyramids linked into sheets through edge- and corner-sharing phosphate and hydrogen phosphate tetrahedra. N-methylimidazolium cations occupy the interstitial space between the uranyl fluorophosphate sheets in 1, whereas 1-ethyl-3-methylimidazolium cations link the uranyl sulfate and phosphate units in 2 and 3 into extended structures.

Toxicity of various anions associated with methoxyethyl methyl imidazolium-based ionic liquids on Clostridium sp.

We investigated the effects on the growth of the anaerobic bacterium, Clostridium sp., of the ionic liquid, 1-methoxyethyl-3-methyl imidazolium [MOEMIM]+, derived from imidazolium cation and paired with one of a variety of counter-ions, viz., tetrafluoroborate [BF4]-, hexafluorophosphate [PF6]-, trifluoroacetate [CF3COO]-, bis(trifluoromethane)sulfonamide [Tf2N]-, methane sulfonate [OMS], and 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF4]. These anions, in association with [MOEMIM]+ lowered the growth rate of the bacterium, showing the following trend: [Tf2N]-≧[PF6]->[BF4]->[CF3COO]->[OMS]−. Anions incorporating fluorine were more toxic than those without it, and their toxicity rose with an increase in the number of fluorine atoms. Also, [MOEMIM]+[BF4]- was less toxic than [BMIM]+[BF4]-, probably due to the presence of a methoxyethyl functional group integrated in the cation side chain.

Surface active and aggregation behavior of methylimidazolium-based ionic liquids of type [C n mim] [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.

Increased enantioselectivity in the enzymatic hydrolysis of amino acid esters in the ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate

The initial rate and enantioselectivity of enzymatic asymmetric hydrolysis of amino acid esters were examined in methylimidazolium-based ionic liquids with anions including tetrafluoroborate, chloride, bromide and bisulfate and in typical organic solvents. Papain displayed much higher enantioselectivity but lower activity in phosphate buffer solution of 1-butyl-3-methylimidazolium tetrafluoroborate BMIM·BF4 than in other media tested (i.e. E=100, V0=0.21 mM min−1 in BMIM·BF4, E=2, V0=0.43 mM min−1 in phosphate buffer, E=14–92, V0=0.22–0.25 mM min−1 in organic solvents for D,L-phenylglycine methyl ester). The influence of BMIM·BF4 on enzyme activity and enantioselectivity also varied with the substrate and the enzyme used. All of the enzymes assayed showed no activity or low enantioselectivity in the ILs with anions including chloride, bromide and bisulfate.