Low-pressure solubilities and thermodynamics of solvation of eight gases in 1-butyl-3-methylimidazolium hexafluorophosphate

Experimental values for the solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon and carbon monoxide in 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6] - a room temperature ionic liquid - are reported as a function of temperature between 283 and 343 K and at pressures close to atmospheric. Carbon dioxide is the most soluble and hydrogen is the least soluble of the gases studied with mole fraction solubilities of the order of 10-2 and 10-4, respectively. All the mole fraction solubilities decrease with temperature except for hydrogen for which a maximum is observed at temperatures close to 310 K. From the variation of solubility, expressed as Henry's law constants, with temperature, the partial molar thermodynamic functions of solvation such as the standard Gibbs energy, the enthalpy, and the entropy are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations, is better than ±1%. © 2005 Elsevier B.V. All rights reserved.

Solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon, and carbon monoxide in 1-butyl-3-methylimidazolium tetrafluoroborate between temperatures 283 K and 343 K and at pressures close to atmospheric

Experimental values for the solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon and carbon monoxide in 1-butyl-3- methylimidazolium tetrafluoroborate, [bmim][BF4] - a room temperature ionic liquid - are reported as a function of temperature between 283 K and 343 K and at pressures close to atmospheric. Carbon dioxide is the most soluble gas with mole fraction solubilities of the order of 10-2. Ethane and methane are one order of magnitude more soluble than the other five gases that have mole fraction solubilities of the order of 10-4. Hydrogen is the less soluble of the gaseous solutes studied. From the variation of solubility, expressed as Henry's law constants, with temperature, the partial molar thermodynamic functions of solvation such as the standard Gibbs energy, the enthalpy, and the entropy are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations is of 1%. © 2005 Elsevier Ltd. All rights reserved.

Unraveling Dynamical Heterogeneity in the Ionic Liquid 1-Butyl-3-methylimidazolium Chloride

Heterogeneous dynamics within a time range of nanoseconds was investigated by molecular dynamics (MD) simulations of 1 -butyl-3-methylimidazolium chloride ([bmim]Cl). After identifying groups of fast and slow ions, it was shown that the separation between the location of the center of mass and the center of charge of cations, d(CMCC), is a signature of such difference in ionic mobility. The distance d(CMCC) can be used as a signature because it relaxes in the time window of the dynamical heterogeneity. The relationship between the parameter dcmcc and conformations of the side alkyl chain in [bmim] is discussed. Since the relatively slow relaxation of dcmcc is a consequence of coexisting polar and nonpolar domains in the bulk, the MD simulations reveal a subtle interplay between structural and dynamical heterogeneity in ionic liquids.

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether, lithium perchlorate, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) with LiClO(4), PEGdME/LiClO(4), and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, PEGdME/[bmim]PF(6), are compared. Raman spectroscopy suggests stronger interactions in PEGdME/LiClO(4) than PEGdmE/[bmim]PF(6), thus corroborating previous results obtained by molecular dynamics simulations. Quantum Chemistry methods have been used to calculate vibrational frequencies and the equilibrium structure of segments of the polymer chain around the cation. A consistent picture has been obtained from Raman spectroscopy, density functional theory (DFT) calculations, and molecular dynamics simulations for these polymer electrolytes. (C) 2010 Elsevier B.V. All rights reserved.

Interactions between 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and gamma-Al2O3 (100) surface calculated by density functional theory

The main aim of this work is to investigate the 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1Im]+[BF4]-) ionic liquid (IL) adsorption on the gamma-Al2O3 (100) by density functional theory calculations to try to rationalize the adsorption as an electrostatic phenomenon. Optimized geometries and interaction energies of IL one-monolayer on the gamma-Al2O3 were obtained on high surface coverage (one cationanion pair per 94.96 nm2). A study of dispersion force was made to estimate its contribution to the adsorption. Overall, the process is ruled by electrostatic interaction between ions and surface. Adsorption of the anion [BF4]- and cation [C4C1Im]+ was also studied by Bader charge analysis and charge density difference for supported and unsupported situations. It is suggested that the IL ions have their charges maintained with significant anion cloud polarization inward to the acid aluminum sites. (c) 2012 Wiley Periodicals, Inc.

Density-viscosity product of small-volume ionic liquid samples using quartz crystal impedance analysis

Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimidazolium. trifluoromethylsulfonate ([C(4)mim][OTf]), were measured. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C(4)mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of similar to 10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of root(rho eta) approximate to 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Using ionic liquid combined with HPLC-DAD to analyze semi-permanent hair dyes in commercial formulations

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Crystal structures of imidazolium bis(trifluoromethanesulfonyl)imide 'ionic liquid' salts: the first organic salt with a cis-TFSI anion conformation

Crystal structures of two examples of an important class of ionic liquids, 1,3-dimethylimidazolium and 1,2,3-triethylimidazolium bis(trifluoromethanesulfonyl)imide have been characterized by single crystal X-ray diffraction. The anion in the 1,3-dimethylimidazolium example (mp 22 degreesC), adopts an unusual cis-geometry constrained by bifurcated cation-anion C-H...O hydrogen-bonds from the imidazolium cation to the anion resulting in the formation of fluorous layers within the solid-state structure. In contrast, in the 1,2,3-triethylimidazolium salt (mp 57 degreesC), the ions are discretely packed with only weak C-H...O contacts between the ions close to the van der Waals separation distances, and with the anion adopting the twisted conformation observed for all other examples from the limited set of organic bis( trifluoromethanesulfonyl) imide crystal structures. The structures are discussed in terms of the favorable physical properties that bis(trifluoromethanesulfonyl) imide anions impart in ionic liquids.

The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

The reduction of guanine was studied by microelectrode voltammetry in the room temperature ionic liquids (RTILs) N-hexyltriethylammonium his (trifluoromethanesulfonyl) imide [N-6.2.2.2][N(Tf)(2)], 1-butyl-3-methylimidazolium hexafluorosphosphate [C(4)mim] [PF6], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C(4)mpyrr][N(Tf)(2)], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C-4mim][N(TF)(2)], N-butyl-N-methyl-pyrrolidinium dicyanamide [C(4)mpyrr][N(NC)(2)] and tris(P-hexyl)-tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P-14,P-6,(6,6)][FAP] on a platinum microelectrode. In [N-6,N-2,N-2,N-2][NTf2] and [P-14,P-6,P-6.6][FAP], but not in the other ionic liquids studied, guanine reduction involves a one-electron, diffusion-controlled process at very negative potential to produce an unstable radical anion. which is thought to undergo a dimerization reaction, probably after proton abstraction from the cation of the ionic liquid. The rate of this subsequent reaction depends on the nature of the ionic liquid, and it is faster in the ionic liquid [P-14,P-6,P-6.6[FAP], in which the formation of the resulting dimer can be voltammetrically monitored at less negative potentials than required for the reduction of the parent molecule. Adenine showed similar behaviour to guanine but the pyrimidines thymine and cytosine did not; thymine was not reduced at potentials less negative than required for solvent (RTIL) decomposition while only a poorly defined wave was seen for cytosine. The possibility for proton abstraction from the cation in [N-6,N-2,N-2,N-2],[NTF2] and [P-14,P-6,P-6.6][FAP] is noted and this is thought to aid the electrochemical dimerization process. The resulting rapid reaction is thought to shift the reduction potentials for guanine and adenine to lower values than observed in RTILs where the scope for proton abstraction is not present. Such shifts are characteristic of so-called EC processes where reversible electron transfer is followed by a chemical reaction. (C) 2009 Elsevier B.V. All rights reserved.

The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

The reduction of guanine was studied by microelectrode voltammetry in the room temperature ionic liquids (RTILs) N-hexyltriethylammonium bis (trifluoromethanesulfonyl) imide [N6,2,2,2][N(Tf)2], 1-butyl-3-methylimidazolium hexafluorosphosphate [C4mim][PF6], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C4mpyrr][N(Tf)2], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][N(Tf)2], N-butyl-N-methyl-pyrrolidinium dicyanamide [C4mpyrr][N(NC)2] and tris(P-hexyl)-tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P14,6,6,6][FAP] on a platinum microelectrode. In [N6,2,2,2][NTf2] and [P14,6,6,6][FAP], but not in the other ionic liquids studied, guanine reduction involves a one-electron, diffusion-controlled process at very negative potential to produce an unstable radical anion, which is thought to undergo a dimerization reaction, probably after proton abstraction from the cation of the ionic liquid. The rate of this subsequent reaction depends on the nature of the ionic liquid, and it is faster in the ionic liquid [P14,6,6,6][FAP], in which the formation of the resulting dimer can be voltammetrically monitored at less negative potentials than required for the reduction of the parent molecule. Adenine showed similar behaviour to guanine but the pyrimidines thymine and cytosine did not; thymine was not reduced at potentials less negative than required for solvent (RTIL) decomposition while only a poorly defined wave was seen for cytosine. The possibility for proton abstraction from the cation in [N6,2,2,2][NTf2] and [P14,6,6,6][FAP] is noted and this is thought to aid the electrochemical dimerization process. The resulting rapid reaction is thought to shift the reduction potentials for guanine and adenine to lower values than observed in RTILs where the scope for proton abstraction is not present. Such shifts are characteristic of so-called EC processes where reversible electron transfer is followed by a chemical reaction. © 2009 Elsevier B.V.

An electrochemical gas sensor based on paper supported room temperature ionic liquids

A sensitive and fast-responding membrane-free amperometric gas sensor is described, consisting of a small filter paper foil soaked with a room temperature ionic liquid (RTIL), upon which three electrodes are screen printed with carbon ink, using a suitable mask. It takes advantage of the high electrical conductivity and negligible vapour pressure of RTILs as well as their easy immobilization into a porous and inexpensive supporting material such as paper. Moreover, thanks to a careful control of the preparation procedure, a very close contact between the RTIL and electrode material can be achieved so as to allow gaseous analytes to undergo charge transfer just as soon as they reach the three-phase sites where the electrode material, paper supported RTIL and gas phase meet. Thus, the adverse effect on recorded currents of slow steps such as analyte diffusion and dissolution in a solvent is avoided. To evaluate the performance of this device, it was used as a wall-jet amperometric detector for flow injection analysis of 1-butanethiol vapours, adopted as the model gaseous analyte, present in headspace samples in equilibrium with aqueous solutions at controlled concentrations. With this purpose, the RTIL soaked paper electrochemical detector (RTIL-PED) was assembled by using 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide as the wicking RTIL and printing the working electrode with carbon ink doped with cobalt(II) phthalocyanine, to profit from its ability to electrocatalyze thiol oxidation. The results obtained were quite satisfactory (detection limit: 0.5 mu M; dynamic range: 2-200 mu M, both referring to solution concentrations; correlation coefficient: 0.998; repeatability: +/- 7% RSD; long-term stability: 9%), thus suggesting the possible use of this device for manifold applications.

Analysis of the isomerism effect on the mutual solubilities of bis(trifluoromethylsulfonyl)imide-based ionic liquids with water

The knowledge of the liquid-liquid equilibria (LLE) between ionic liquids (ILs) and water is of utmost importance for environmental monitoring, process design and optimization. Therefore, in this work, the mutual solubilities with water, for the ILs combining the 1-methylimidazolium, [C(1)im](+); 1-ethylimidazolium, [C(2)im](+); 1-ethyl-3-propylimidazolium, [C(2)C(3)im](+); and 1-butyl-2,3-dimethylimidazolium, [C(4)C(1)C(1)im](+) cations with the bis(trifluoromethylsulfonyl)imide anion, were determined and compared with the isomers of the symmetric 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ([C(n)C(n)im][NTf2], with n=1-3) and of the asymmetric 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(n)C(1)im][NTf2], with n = 2-5) series of ILs. The results obtained provide a broad picture of the impact of the IL cation structural isomerism, including the number of alkyl side chains at the cation, on the water-IL mutual solubilities. Despite the hydrophobic behaviour associated to the [NTf2](-) anion, the results show a significant solubility of water in the IL-rich phase, while the solubility of ILs in the water-rich phase is much lower. The thermodynamic properties of solution indicate that the solubility of ILs in water is entropically driven and highly influenced by the cation size. Using the results obtained here in addition to literature data, a correlation between the solubility of [NTf2]-based ILs in water and their molar volume, for a large range of cations, is proposed. The COnductor like Screening MOdel for Real Solvents (COSMO-RS) was also used to estimate the LLE of the investigated systems and proved to be a useful predictive tool for the a priori screening of ILs aiming at finding suitable candidates before extensive experimental measurements.

Raman and ab initio studies of simple and binary 1-Alkyl-3-methylimidazolium ionic liquids

<p>Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF(6)]), 1-hexyl-3-methylimidazolium chloride ([C(6)mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)mim][PF(6)]), and binary mixtures thereof, have been assigned using ab initio MP2 calculations. The previously reported anti and gauche forms of the [C(4)mim](+) cation have been observed, and this study reveals this to be a general feature of the long-chain I-alkyl derivatives. Analysis of mixtures Of [C(6)mim]Cl and [C(6)mim][PF(6)] has provided information on the nature of the hydrogen bonding between the imidazolium headgroup and the anions, and the invariance of the essentially 50:50 mixture of the predominant conformers informs on the nature of glass formation in these systems.</p>

Effect of Water on the Electrochemical Window and Potential Limits of Room-Temperature Ionic Liquids

The effect of water content on room-temperature ionic liquids (RTILs) was studied by Karl Fischer titration and cyclic voltammetry in the following ionic liquids: tris(P-hexyl)tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P-14,P-6,P-6,P-6][NTf2], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [C(4)mpyrr][NTf2], 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate [C(6)mim][FAP], 1-butyl3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)mim][NTf2], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)dmim][NTf2], N-hexyltriethylammonium bis(trifluoromethylsolfonyl)imide [N-6,N-2,N-2,N-2][NTf2], 1-butyl-3-methylirnidazolium hexafluorophosphate [C(4)mim][PF6], F6], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(2)mim][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)mim][BF4], 1-hexyl-3-methylimidazolium iodide [C(4)mim][I], 1-butyl-3-methylimidazolium trifluoromethylsulfonate [C(4)mim][OTf], and 1-hexyl-3-methylimidazolium chloride [C(6)mim][Cl]. In addition, electrochemically relevant properties such as viscosity, conductivity, density, and melting point of RTILs are summarized from previous literature and are discussed. Karl Fisher titrations were carried out to determine the water content of RTILs for vacuum-dried, atmospheric, and wet samples. The anion in particular was found to affect the level of water uptake. The hydrophobicity of the anions adhered to the following trend: [FAP](-) &gt; [NTf2](-) &gt; [PF6](-) &gt; [BF4](-) &gt; halides. Cyclic voltammetry shows that an increase in water content significantly narrows the electrochemical window of each ionic liquid. The electrochemical window decreases in the following order: vacuum-dried &gt; atmospheric &gt; wet at 298 K &gt; 318 K &gt; 338 K. The anodic and cathodic potentials vs ferrocene internal reference are also listed under vacuum-dried and atmospheric conditions. The data obtained may aid the selection of a RTIL for use as a solvent in electrochemical applications.

Density and viscosity of several pure and water-saturated ionic liquids

Densities and viscosities were measured as a function of temperature for six ionic liquids (1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium ethylsulfate and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide. The density and the viscosity were obtained using a vibrating tube densimeter from Anton Paar and a rheometer from Rheometrics Scientific at temperatures up to 393 K and 388 K with an accuracy of 10-3 g cm-3 and 1%, respectively. The effect of the presence of water on the measured values was also examined by studying both dried and water-saturated samples. A qualitative analysis of the evolution of density and viscosity with cation and anion chemical structures was performed. © The Royal Society of Chemistry 2006.