Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Aggregation behavior of alkyl triphenyl phosphonium bromides in aprotic and protic ionic liquids

The aggregation behavior of alkyltriphenylphonium bromides, C _n TPB (n?=?12 and 14), has been investigated in two different room-temperature ionic liquids (ILs), the aprotic 1-butyl-3-metyllimidazolium tetrafluoroborate ([bmim][BF₄]), and the protic ethylammonium nitrate (EAN). The critical micelle concentration was determined by the surface tension measurements. The calculated thermodynamic parameters based on surface tension measurements at various temperatures indicate that the micellization for C _n TPB in both aprotic [bmim][BF₄] and protic EAN is enthalpy-driven. But stronger solvophobic interactions presented between C _n TPB and protic EAN than aprotic [bmim][BF₄]. ¹H NMR spectra were further conducted to reveal that ethylammonium cation can insert into the micelle while imidazole cation only locates among the head groups of C _n TPB.     

1-Butyl-3-methylimidazolium p-toluenesulfinate: a novel reagent for synthesis of sulfones and β-ketosulfones in ionic liquid

A novel task-specific ionic liquid, 1-butyl-3-methylimidazolium p-toluenesulfinate, [bmim][p-TolSO₂] has been synthesized and used as a nucleophile for the reaction with alkyl bromides and phenacyl bromides to prepare sulfones and β-ketosulfones in excellent yields (80-93%) in [bmim][BF₄] ionic liquid. The isolated yields of sulfones and β-ketosulfones were higher in [bmim][BF₄] than other organic solvents at room temperature.     

Investigation on the Complexation of Dioxovanadium (V) with D-(-)-Quinic Acid in Water + 1-Butyl-3-Methylimidazolium Tetrafluoroborate and Water + Methanol Mixed Solvents Using the KAT Model

The complex formation reaction of the $ {\text{VO}}_{2}^{ + } $ VO 2 + cation with D-(-)-quinic acid {(1R,3R,4S,5R)-(-)-1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid} at T = 298 K, I = 0.1 mol·dm^?3 of sodium chloride in various aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF₄, and methanol were studied by using potentiometric and UV spectrophotometric techniques. As far as we know, the calculated stability constants data presented in the current work are the first reported values for [bmim]BF₄ and methanol mixed solvents. The Kamlet–Abboud–Taft solvatochromic equation enabled us to interpret the UV data and the stability constants values. The Redlich–Kister equation was applied for the calculation of solvatochromic parameters in the binary water + [bmim]BF₄ mixtures. Hydrogen bonding is important for the dissociation constant in both media. In these systems the solvent polarizability and hydrogen-bond donor ability are the main interactions for the stability constants in the aqueous ionic liquid and methanol solutions, respectively.     

Synthesis of gold nanoparticles in sol–gel glass porogens containing [bmim][BF4] ionic liquid

The [bmim][BF₄] ionic liquid effect on gold nanoparticles formation in silica sol–gel materials is studied in order to produce gel-derived glasses with optical properties. The characteristic red color from gold nanoparticles is observed for transparent glass monoliths obtained sintering, between 365 and 425 °C, a silica sol–gel precursor containing HAuCl₄·3H₂O and [bmim][BF₄], under normal atmospheric conditions. The effect of sintering the ionogel at different temperatures (T_sint) or times (t_sint) on the optical properties, shape, size, and distribution of gold nanoparticles is discussed. Presence of the gold particles is observed using transmission electron microscopy images followed by energy dispersive X-ray spectroscopy analysis. The thermal decomposition of [bmim][BF₄] in the ionogel is investigate using calorimetric and spectroscopic techniques, and by analysis of volatile compounds released by the sol–gel material during sintering. With these results a mechanism for the formation of the gold nanoparticles is proposed, where a first ionic liquid degradation step provides the reductive environment that enables the gold nanoparticles production at the range of temperatures between 350 and 425 °C. Upon sintering the synthesized materials the ionic liquid acts as a sacrificial additive and the ionic liquid thermal decomposition products enables the formation of gold nanoparticles in the sol–gel matrix.     

Ionic Liquid: A Good Pressure Transmitting Medium

A potential new use of room temperature ionic liquid for a pressure transmitting medium is introduced in detail. A systematic study of the pressure-induced solidification of 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄MIM][BF₄]) is presented in a diamond anvil cell at pressures up to 30 GPa by combining ruby fluorescence and synchrotron X-ray diffraction measurements. Its hydrostatic properties have been determined with hydrostatic limit up to about 6 GPa, and a slight pressure gradient was found up to 21 GPa. These results indicate that this kind of ionic liquid is a good hydrostatic pressure transmitting medium.     

Amine basicity: measurements of ion pair stability in ionic liquid media

The stability constants relevant to the formation of amine/p-nitrophenol ion pairs have been determined in [bmim][BF₄] solution, in the presence of butylamine, piperidine, and triethylamine, by using spectrophotometric measurements. In order to evaluate how the ion pair stability is affected by ionic liquid structure, piperidine has been chosen as model amine for studies in [bmim][PF₆], [bmim][NTf₂], [bm₂im][NTf₂] and in several [bmim][BF₄]/1,4-dioxane binary mixtures. Data obtained in ionic liquid solutions have been compared with those previously reported in conventional organic solvents.     

Optical Spectroscopic Studies on Structural Changes of Helical-rich Proteins in Aqueous Solutions of Ionic Liquids

We have investigated structural changes of myoglobin and cytochrome c, which are helical-rich proteins, in aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions by Fourier transform infrared and circular dichroism spectroscopy. At low [bmim][Cl] concentrations {X (mol% IL) < 10}, both proteins unfold. Remarkably, at high [bmim][Cl] concentrations (X > 10), myoglobin aggregates whereas cytochrome c refolds its α-helical structure. The tertiary structures of both proteins are disrupted over the entire range of studied [bmim][Cl] concentrations. Our results suggest that, in aqueous solutions at high [bmim][Cl] concentrations, the differences in structural transitions between myoglobin and cytochrome c might be due to the difference in hydration between these proteins.     

A characteristic effect of pressure on inclusion complexation of phenothiazine dyes with p-sulfonatocalix[6]arene in a room-temperature ionic liquid

The inclusion complexation of p-sulfonatocalix[6]arene (Calix-S6) with three kinds of phenothiazine dyes was studied spectrophotometrically in a mixture of a room-temperature ionic liquid [bmim]BF₄ (1-butyl-3-methylimidazolium tetrafluoroborate) and ethanol. We have determined the association constants of Calix-S6 with phenothiazine dyes under external static pressure up to 767 bar in the [bmim]BF₄-ethanol and alcohol-water mixtures. With increasing external pressure, the inclusion equilibrium in the alcohol-water mixtures was shifted to the dissociation side. Conversely, the inclusion equilibrium of methylene blue (MB) and azure A (AA) in the ionic liquid mixture was shifted to the association side. From the analysis of the pressure effects, the reaction volumes ΔV for inclusion complexation were estimated as −7 to 9 cm³ mol⁻¹ in the [bmim]BF₄-ethanol mixture and 20–32 cm³ mol⁻¹ in the alcohol-water mixtures. Based on the results, we have suggested that there is a competing complexation between the included dye and [bmim]BF₄ molecules in the ionic liquid.     

A comparative study on the ionic liquid [bmim][BF4] and its solution with transient absorption spectroscopy

A detailed study was explored to compare the transient absorption spectra of the neat 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) with its solution in water or acetonitrile. It was concluded that the excited triplet state ³[bmim]^+* was produced after 266 nm laser irradiation, and then the neutral radical [bmim] and the cation radical [bmim] ²⁺ were formed through two possible paths. The transient absorption spectra of the neat [bmim][BF₄] and its solution were similar but the reaction kinetics were different due to their different local structures such as dimeric or cluster. The energy transfer between excited [bmim][BF₄] and β-carotene further affirmed the existence of ³[bmim]^+*. And the reaction that the hydrated electron captured by [bmim]⁺ to produce [bmim] in solution was observed.     

Combined dealkoxycarbonylation and lactonisation of unsaturated malonates in ionic liquids

Heating unsaturated malonates with LiCl and water in [bmim][Br] or [bmim][BF₄]/[bmim][Br] produces unsaturated esters or lactones, respectively.     

Ionic liquid-catalyzed and microwave-assisted syntheses of pyrrolizine- and indolizinedione derivatives

3H-Pyrrolo[2,1-a]isoindole-2,5-diones and isoindolo[2,1-a]quinoline-5,11-diones were synthesized by intramolecular cyclization of N-[2-oxo-3-(triphenyl-??⁵-phosphanylidene)propyl]- and N-[2-(triphenyl-??⁵-phosphanylidene)acetyl]phthalimides, respectively, in the presence of ionic liquid ([bmim][BF₄], 10 mol %) as catalyst or under microwave irradiation.     

Ionic liquid-mediated Darzens condensation: An environmentally-friendly procedure for the room-temperature synthesis of α,β-epoxy ketones

This room-temperature Darzens condensation of α-chloroacetophenone with various aromatic aldehydes mediated by [bmim][BF₄] ionic liquid in the presence of sodium tert-butoxide resulted in the sole formation of good to excellent yields of trans-α,β-epoxy ketones in short time periods. In contrast, tert-butyl 2-chloroacetate underwent Darzens reactions with aldehydes giving mixtures of both cis and trans products with low selectivity. In all reactions, the ionic liquid was recovered and reused in the subsequent reactions without significant loss of activity.     

Electrochemical property and analysis application of biosensors in miscible nonaqueous media—Room-temperature ionic liquid

Stable heme proteins entrapped in dimethylformamide (DMF)–chitosan organohydrogel films modified electrodes were operated in neat hydrophilic room-temperature ionic liquid (IL) [bmim][BF₄] for the first time. The modified electrodes possess outstanding electrochemical response in [bmim][BF₄] without adding water. The morphology studies of films were demonstrated by atomic force microscopy (AFM). UV–Vis and FTIR spectroscopy showed that the heme proteins retained their native structure in organohydrogel films. Direct electrochemistry and bioelectrocatalysis of heme protein–organohydrogel films were investigated. Several electrochemical parameters such as the charge transfer coefficients (α) and the apparent electron transfer rate constant (k_s) of these processes were calculated by performing nonlinear regression analysis of square wave voltammetry (SWV) experimental dates. Furthermore, high electrocatalytic activity to hydrogen peroxide (H₂O₂) was observed, indicating that heme proteins entrapped in organohydrogel films retained their bioelectrocatalytic activities in [bmim][BF₄]. Kinetic analysis of the cyclic voltammetry dates shows that heme protein–organohydrogel films operated in IL bring up to an enhancement of the biosensor sensitivity and a high affinity for H₂O_2.     

Solvent Effect on the Enthalpy of Solution and Partial Molar Volume of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate

Enthalpies of solution and partial molar volumes of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate were determined in 15 solvents of different polarity. Very large differences of the enthalpies of solution (????_sol H _IL=38.9?kJ?mol^?1) and partial molar volumes (??V _IL=43 cm³?mol^?1) are nearly the same as observed for lithium perchlorate solutions. These results clearly indicate that the low values of the macroscopic polarity parameters of [bmim]BF₄ do not correspond with the large differences of the intermolecular interactions in IL solutions. The values of the partial molar volume of the cation, $V_{[\mathrm{bmim}]^{+}}$ , were estimated for the first time. The changes of the partial molar volumes, V _IL, reflect mainly the changes of anion volume, $V_{\mathrm{BF}_{4}^{-}}$ . The rate of the Diels?CAlder reaction of 9,10-dimethylanthracene with maleic anhydride in the [bmim]BF₄ medium was nearly the same as in common molecular solvents.     

On the characterization of some [bmim][X]/co-solvent binary mixtures: a multidisciplinary approach by using kinetic, spectrophotometric and conductometric investigations

In order to study the intrinsic characteristics and to evaluate the structural variations determined by the addition of a co-solvent to 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) we examined the behaviour of some probes in [bmim][BF₄]/co-solvent binary mixtures. The rate constants of the piperidino-catalyzed rearrangement of the Z-phenylhydrazone of the 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole as well as the spectrometric properties of pyrene and Nile Red were evaluated. With the same purpose also ¹H NMR and conductivity measurements were carried out. By comparison the behaviour of 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonylimide)/1,4-dioxane mixtures has been analyzed. The whole of data confirms the presence of weak interactions that determine a partially preorganized structure for [bmim][X]. This is perturbed at some degrees by quantity and nature of guest molecules. For example conductivity measurements support the idea that different charged aggregates are present in the [bmim][X]/co-solvent binary mixtures.     

Conformational analysis,barriers to internal rotation,vibrational assignment and ab initio calculations of chloroacetone

The infrared (3500-20 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra have been recorded for gaseous and solid chloroacetone (1-chloro-2-propanone), CH₂ClC(O)CH₃. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis that the molecule exists predominantly in a gauche conformation having a “near cis” structure of C₁ symmetry (dih ClCCO=142°C) in the vapor but for the liquid a second conformer having a trans structure (chlorine atom oriented trans to the methyl group) with C_s point group symmetry is present. From a study of the Raman spectrum of the liquid at variable temperatures, the trans conformation has been determined to be more stable than the gauche form by 1042±203 cm⁻¹ (2.98±0.6 kcal mol⁻¹ and is the only conformer present in the spectrum of the annealed solid. From ab initio calculations at the 3-21G* and 6-31G* basis set levels optimized geometries for both the gauche and trans conformers have been obtained and the potential surfaces governing internal rotation of the symmetric and asymmetric rotors have been obtained. The observed vibrational frequencies and assignments to the fundamental vibrations for both the gauche and trans conformers are compared to those calculated with the 3-21G* basis set. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

CsF/[bmim][BF4]: An efficient and reusable system for Henry reaction

Cesium fluorides in ionic liquid [bmim][BF₄] have been used to promote the Henry reaction effectively. These reactions proceed smoothly and afford an excellent yield of the products.     

Layered structure of room-temperature ionic liquids in microemulsions by multinuclear NMR spectroscopic studies

Microemulsions form in mixtures of polar, nonpolar, and amphiphilic molecules. Typical microemulsions employ water as the polar phase. However, microemulsions can form with a polar phase other than water, which hold promise to diversify the range of properties, and hence utility, of microemulsions. Here microemulsions formed by using a room‐temperature ionic liquid (RTIL) as the polar phase were created and characterized by using multinuclear NMR spectroscopy. ¹H, ¹¹B, and ¹⁹F NMR spectroscopy was applied to explore differences between microemulsions formed by using 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF₄]) as the polar phase with a cationic surfactant, benzylhexadecyldimethylammonium chloride (BHDC), and a nonionic surfactant, Triton X‐100 (TX‐100). NMR spectroscopy showed distinct differences in the behavior of the RTIL as the charge of the surfactant head group varies in the different microemulsion environments. Minor changes in the chemical shifts were observed for [bmim]⁺ and [BF₄]^? in the presence of TX‐100 suggesting that the surfactant and the ionic liquid are separated in the microemulsion. The large changes in spectroscopic parameters observed are consistent with microstructure formation with layering of [bmim]⁺ and [BF₄]^? and migration of Cl^? within the BHDC microemulsions. Comparisons with NMR results for related ionic compounds in organic and aqueous environments as well as literature studies assisted the development of a simple organizational model for these microstructures.     

Activity and stability of horseradish peroxidase in hydrophilic room temperature ionic liquid and its application in non-aqueous biosensing

The activity and stability of horseradish peroxidase (HRP) were investigated in a hydrophilic room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluroborate ([bmim][BF₄]) by electrochemical methods. Although no detectable activity exhibited in anhydrous [bmim][BF₄], HRP was active in the presence of a small amount of water (4.53%, v/v). And its activity can be improved by immobilization in agarose hydrogel. The immobilized HRP possesses excellent activity at 65 °C. It remained 80.2% of its initial activity after being immersed for 10.5 h in an aqueous mixture of [bmim][BF₄] with some hydrogen peroxide (H₂O₂) under room temperature, implying extremely high stability. Moreover, the immobilized HRP was found to be very sensitive and stable in H₂O-containing [bmim][BF₄] for the detection of H₂O₂, with a wide linear range of 6.10 × 10⁻⁷ to 1.32 × 10⁻⁴ mol l⁻¹ and low detection limit of 1.0 × 10⁻⁷ mol l⁻¹.