Chemistry in heterocyclic ammonium fluorohydrogenate room-temperature ionic liquid

Investigation on alkali fluoride-HF system has been initiated in the 19th century. The technique is currently utilized in fluorine-chemical industry. But, the problem is that this system readily releases hazardous HF. Although organic base, e.g., amine, with HF, which is mainly applied to fluorination treatment for organic compound, reduces the HF release, the solution still requires careful handling because of limited amount of free HF. Recently family of fluorohydrogenate room-temperature ionic liquid, XF(HF)_2.3, that consists of heterocyclic ammonium cation (X⁺), F(HF)₂⁻, and F(HF)₃⁻, has gotten a lot of attentions due to the interesting physicochemical properties such as negligible vapor pressure (<7.5 × 10⁻³ Torr (=1 Pa) at 298 K), high conductivity, and low corrosiveness. This novel solvent will greatly contribute to development of fluorine chemistry. In this article, fundamental techniques and physicochemical data on the fluorohydrogenate RTIL are summarized, and molecular science in the dialkylimidazolium fluorohydrogenates leading to the understanding of the unusual properties is reviewed based on recent experimental and theoretical considerations.     

Phase behavior and microstructure of microemulsions with a room-temperature ionic liquid as the polar phase

Microemulsions of nonionic alkyl oligoethyleneoxide (CiEj) surfactants, alkanes, and ethylammonium nitrate (EAN), a room-temperature ionic liquid, have been prepared and characterized. Studies of phase behavior reveal that EAN microemulsions have many features in common with corresponding aqueous systems, the primary difference being that higher surfactant concentrations and longer surfactant tailgroups are required to offset the decreased solvophobicity the surfactant molecules in EAN compared with water. The response of the EAN microemulsions to variation in the length of the alkane, surfactant headgroup, and surfactant tailgroup has been found to parallel that observed in aqueous systems in most instances. EAN microemulsions exhibit a single broad small-angle X-ray scattering peak, like aqueous systems. These are well described by the Teubner-Strey model. A lamellar phase was also observed for surfactants with longer tails at lower temperatures. The scattering peaks of both microemulsion and lamellar phases move to lower wave vector on increasing temperature. This is ascribed to a decrease in the interfacial area of the surfactant layer. Phase behavior, small-angle X-ray scattering, and conductivity experiments have allowed the weakly to strongly structured transition to be identified for EAN systems.     

Electrodeposition of platinum nanoparticles in a room-temperature ionic liquid

The electrochemistry of the [PtCl(6)](2-)-[PtCl(4)](2-)-Pt redox system on a glassy carbon (GC) electrode in a room-temperature ionic liquid (RTIL) [i.e., N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMEBF(4))] has been examined. The two-step four-electron reduction of [PtCl(6)](2-) to Pt, i.e., reduction of [PtCl(6)](2-) to [PtCl(4)](2-) and further reduction of [PtCl(4)](2-) to Pt, occurs separately in this RTIL in contrast to the one-step four-electron reduction of [PtCl(6)](2-) to Pt in aqueous media. The cathodic and anodic peaks corresponding to the [PtCl(6)](2-)/[PtCl(4)](2-) redox couple were observed at ca. -1.1 and 0.6 V vs a Pt wire quasi-reference electrode, respectively, while those observed at -2.8 and -0.5 V were found to correspond to the [PtCl(4)](2-)/Pt redox couple. The disproportionation reaction of the two-electron reduction product of [PtCl(6)](2-) (i.e., [PtCl(4)](2-)) to [PtCl(6)](2-) and Pt metal was also found to occur significantly. The electrodeposition of Pt nanoparticles could be carried out on a GC electrode in DEMEBF(4) containing [PtCl(6)](2-) by holding the potential at -3.5 or -2.0 V. At -3.5 V, the four-electron reduction of [PtCl(6)](2-) to Pt can take place, while at -2.0 V the two-electron reduction of [PtCl(6)](2-) to [PtCl(4)](2-) occurs. The results obtained demonstrate that the electrodeposition of Pt at -3.5 V may occur via a series of reductions of [PtCl(6)](2-) to [PtCl(4)](2-) and further [PtCl(4)](2-) to Pt and at -2.0 V via a disproportionation reaction of [PtCl(4)](2-) to [PtCl(6)](2-) and Pt. Furthermore, the deposition potential of Pt nanoparticles was found to largely influence their size and morphology as well as the relative ratio of Pt(110) and Pt(100) crystalline orientation domains. The sizes of the Pt nanoparticles prepared by holding the electrode potential at -2.0 and -3.5 V are almost the same, in the range of ca. 1-2 nm. These small nanoparticles are "grown" to form bigger particles with different morphologies: In the case of the deposition at -2.0 V, the GC electrode surface is totally, relatively compactly covered with Pt particles of relatively uniform size of ca. 10-50 nm. On the other hand, in the case of the electrodeposition at -3.5 V, small particles of ca. 50-100 nm and the grown-up particles of ca. 100-200 nm cover the GC surface irregularly and coarsely. Interestingly, the Pt nanoparticles prepared by holding the potential at -2.0 and -3.5 V are relatively enriched in Pt(100) and Pt(110) facets, respectively.     

Extraction of lanthanides from aqueous solution by using room-temperature ionic liquid and supercritical carbon dioxide in conjunction

For the first time, the study of a three-step extraction system of water/ionic liquid/supercritical CO2 has been performed. Extraction of trivalent lanthanum and europium from an aqueous nitric acid solution to a supercritical CO2 phase via an imidazolium-based ionic liquid phase is demonstrated, and extraction efficiencies higher than 87 % were achieved. The quantitative extraction is obtained by using different fluorinated beta-diketones with and without the addition of tri(n-butyl)phosphate. The complexation phenomenon occurring in the room-temperature ionic-liquid (RTIL) phase was evidenced by using luminescence spectroscopy.     

A highly fluorous room-temperature ionic liquid exhibiting fluorous biphasic behavior and its use in catalyst recycling

[formula: see text] A novel fluorous room-temperature ionic liquid, 1-butyl-3-methyl-imidazolium tetrakis[p-[dimethyl(1H, 1H, 2H, 2H-perfluorooctyl)silyl]phenyl]-borate (1), was used as a solvent for the homogeneous hydrosilylation of 1-octene catalyzed by a fluorous version of Wilkinson's catalyst. The catalyst was recycled by biphasic separation with an average retention of catalyst activity of 94%. As opposed to other ionic liquids, 1 exhibits high miscibility with apolar compounds such as alkenes and resembles fluorous solvents in its phase behavior with organic solvents.     

Lithium secondary batteries using modified-imidazolium room-temperature ionic liquid

Highly reversible, safe lithium secondary batteries that use imidazolium-cation-based room-temperature ionic liquid as an electrolyte and lithium metal as an anode material were realized by the molecular design. To achieve higher reduction stability, an electron-donating substituent was introduced to promote charge delocalization in the imidazolium cation of room-temperature ionic liquids.     

Electrostatic layer-by-layer deposition and electrochemical characterization of thin films composed of MnO2 nanoparticles in a room-temperature ionic liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.     

Anisotropic ionogels of sodium laurate in a room-temperature ionic liquid

Anisotropic thermally reversible ionogels of sodium laurate (SL) were prepared in the first discovered room-temperature ionic liquid (RTIL), ethylammonium nitrate (EAN). Polarized optical microscope images indicate that the gels are birefringent, illuminating the presence of anisotropic structures. Small-angle X-ray scattering results reveal that SL and lauric acid (LA) molecules are arranged to form lamellar structures, but no SL crystallites were confirmed by the X-ray diffraction measurements. With an increase of the SL concentration, the interlayer distance decreases. Rheological measurements indicate that the anisotropic ionogels are highly viscoelastic and the storage modulus (G') increases with an increase of the SL concentration in EAN. Electrochemical measurements indicate that the anisotropic ionogels may have potential applications in electrochemical fields. The intermolecular hydrogen bond as well as the solvatophobic interaction of SL and LA formed by a chemical reaction, CH(3)(CH(2))(10)COONa + CH(3)CH(2)NH(3)NO(3) --> CH(3)CH(2)NH(2) upward arrow + NaNO(3) downward arrow + CH(3)(CH(2))(10)COOH, can play a role in the formation of three-dimensional networks having lamellar structures which are responsible for the anisotropic ionogels. The formation of anisotropic ionogels by surfactants in RTILs could be a new phenomenon, but this is not a very classic case of organogels.     

Phase transition and conductive acceleration of phosphonium-cation-based room-temperature ionic liquid

An unusual ionic conduction phenomenon related to the phase transition of a novel phosphonium-cation-based room-temperature ionic liquid (RTIL) is reported; we found that in the phase change upon cooling, a clear increase in ionic conductivity was seen as the temperature was lowered, which differs from widely known conventional RTILs; clearly, our finding of abnormality of the correlation between temperature change and ionic conduction is the first observation in the electrolyte field.     

Outstanding room-temperature capacitance of biomass-derived microporous carbons in ionic liquid electrolyte

A remarkable capacitance of 180 F·g^− 1 (at 5 mV·s^− 1) in solvent-free room-temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was achieved in symmetric supercapacitors using microporous carbons with a specific surface area of ca. 2000 m²·g^− 1 calculated from gas sorption by the 2D-NLDFT method. The efficient capacitive charge storage was ascribed to textural properties: unlike most activated carbons, high specific surface area was made accessible to the bulky ions of the ionic liquid electrolyte thanks to micropores (1–2 nm) enabled by fine-tuning chemical activation. From the industrial perspective, a high volumetric capacitance of ca. 80 F·cm^− 3 was reached in neat ionic liquid due to the absence of mesopores. The use of microporous carbons from biomass waste represents an important advantage for large-scale production of high energy density supercapacitors.     

On the diffusion of ferrocenemethanol in room-temperature ionic liquids: an electrochemical study

The electrochemical behaviour of ferrocenemethanol (FcMeOH) has been studied in a range of room-temperature ionic liquids (RTILs) using cyclic voltammetry, chronoamperomery and scanning electrochemical microscopy (SECM). The diffusion coefficient of FcMeOH, measured using chronoamperometry, decreased with increasing RTIL viscosity. Analysis of the mass transport properties of the RTILs revealed that the Stokes-Einstein equation did not apply to our data. The "correlation length" was estimated from diffusion coefficient data and corresponded well to the average size of holes (voids) in the liquid, suggesting that a model in which the diffusing species jumps between holes in the liquid is appropriate in these liquids. Cyclic voltammetry at ultramicroelectrodes demonstrated that the ability to record steady-state voltammograms during ferrocenemethanol oxidation depended on the voltammetric scan rate, the electrode dimensions and the RTIL viscosity. Similarly, the ability to record steady-state SECM feedback approach curves depended on the RTIL viscosity, the SECM tip radius and the tip approach speed. Using 1.3 μm Pt SECM tips, steady-state SECM feedback approach curves were obtained in RTILs, provided that the tip approach speed was low enough to maintain steady-state diffusion at the SECM tip. In the case where tip-induced convection contributed significantly to the SECM tip current, this effect could be accounted for theoretically using mass transport equations that include diffusive and convective terms. Finally, the rate of heterogeneous electron transfer across the electrode/RTIL interface during ferrocenemethanol oxidation was estimated using SECM, and k(0) was at least 0.1 cm s(-1) in one of the least viscous RTILs studied.     

Reversed-phase liquid chromatographic method for the determination of selected room-temperature ionic liquid cations

The separation of selected 1-alkyl- and 1-aryl-3-methylimidazolium-based room temperature ionic liquid cations has been performed using reversed-phase high-performance liquid chromatography with electrospray ionization mass detection. The RP-HPLC method development started with the selection of a column taking into account especially the resolution of low molecular congeners of the selected group. Mobile phase composition was optimized for peak resolution, sensitivity and high reproducibility of retention values. The results of the method development were applied to the determination of exemplary ionic liquid species present in the medium used in cytotoxicity studies.     

Effect of polar solvent acetonitrile on the electrochemical behavior of polyaniline in ionic liquid electrolytes

Polyaniline film was electropolymerized in organic acidic media (CF3COOH) and then investigated by cyclic voltammetry, AC impedance, and galvanostatic charging and discharging tests in ionic liquid-1-methyl-3-butylimidazolium hexafluorophosphate (BMIPF6) and the mixture electrolytes of BMIPF6 and acetonitrile (ACN) with different ratios. The results showed that the polymer in mixture of BMIPF6 and ACN have lower solution resistance, higher cycle life, and higher electrochemical capacitance. The relationship of the peak current to the scan rates provides some insight into the nature of the polyaniline film switching reaction in different electrolytes.     

Excess thermodynamic properties in mixtures of a representative room-temperature ionic liquid and acetonitrile

The nature of the interactions between a representative room-temperature ionic liquid, namely 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF(4)]) and a common organic solvent, acetonitrile (CH(3)CN) has been investigated by means of Brillouin light scattering, over the whole concentration range and in the temperature range from -20 to 45 degrees C. Negative deviations from the ideal behavior of both molar volumes and adiabatic compressibility have been observed. This result has been interpreted within the framework of a well-established theoretical model, namely a nonadditive hard-sphere mixture. Despite that similar findings were rationalized in terms of enhanced interactions between molecules, a more detailed analysis of excess thermodynamic functions indicates that they are mainly due to excluded volume effects and that the differences in local intermolecular interactions act as higher order contributions: we have found that this can be a general feature of liquid mixtures. On this basis we present a reconsideration for excess thermodynamic data and for their role in providing direct information on intermolecular interactions.     

Vibrational energy relaxation of a diatomic molecule in a room-temperature ionic liquid

Vibrational energy relaxation (VER) dynamics of a diatomic solute in ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI(+)PF(6) (-)) are studied via equilibrium and nonequilibrium molecular dynamics simulations. The time scale for VER is found to decrease markedly with the increasing solute dipole moment, consonant with many previous studies in polar solvents. A detailed analysis of nonequilibrium results shows that for a dipolar solute, dissipation of an excess solute vibrational energy occurs almost exclusively via the Lennard-Jones interactions between the solute and solvent, while an oscillatory energy exchange between the two is mainly controlled by their electrostatic interactions. Regardless of the anharmonicity of the solute vibrational potential, VER becomes accelerated as the initial vibrational energy increases. This is attributed primarily to the enhancement in variations of the solvent force on the solute bond, induced by large-amplitude solute vibrations. One interesting finding is that if a time variable scaled with the initial excitation energy is employed, dissipation dynamics of the excess vibrational energy of the dipolar solute tend to show a universal behavior irrespective of its initial vibrational state. Comparison with water and acetonitrile shows that overall characteristics of VER in EMI(+)PF(6) (-) are similar to those in acetonitrile, while relaxation in water is much faster than the two. It is also found that the Landau-Teller theory predictions for VER time scale obtained via equilibrium simulations of the solvent force autocorrelation function are in reasonable agreement with the nonequilibrium results.     

Spectroelectrochemical identification of a pentavalent uranyl tetrachloro complex in room-temperature ionic liquid

Reduction of U(VI)O(2)Cl(4)(2-) in a mixture of 1-ethyl-3-methylimidazolium tetrafluoroborate and its chloride at E°' = -0.996 V vs Fc/Fc(+) and 298 K affords U(V)O(2)Cl(4)(3-), which is kinetically stable and exhibits typical character of U(V) in the UV-vis-NIR absorption spectrum.     

Adsorption of phytosterol ethoxylates on silica in an aprotic room-temperature ionic liquid

The adsorption of a nonionic surfactant at a silica/room-temperature ionic liquid interface has been characterized on the basis of analytical data obtained through a combination of surface force measurements, in situ soft-contact atomic force microscope (AFM) images, and quartz crystal microbalance with dissipation monitoring (QCM-D) data. The surfactant employed in this study is a kind of phytosterol ethoxylate (BPS-20), and the ionic liquid selected here is aprotic 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI). This ionic liquid spontaneously forms solvation layers on silica, being composed of an Emim(+) cation layer and EmimTFSI ion pair layers. The addition of BPS-20 disrupts these solvation layers and suggests a surfactant layer adsorbed at the interface. This is the first report demonstrating the adsorption of nonionic surfactants at the solid/aprotic ionic liquid interface.     

Lyotropic liquid crystalline phases formed by phyosterol ethoxylates in room-temperature ionic liquids

The phase behaviors of four phytosterol ethoxylates surfactants (BPS-n, n = 5, 10, 20, and 30) with different oxyethylene units in room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), have been studied. The polarized optical microscopy and small-angle X-ray scattering techniques are used to characterize the phase structures of these binary systems at 25 °C. The structure and ordering of the liquid crystalline (LC) phases in such BPS-n/[Bmim]BF₄ systems are found to be influenced by BPS-n concentration and the temperature. Due to the bulky and rigid cholesterol group, the phytosterol ethoxylates surfactants exhibit different properties and interaction mechanism from the conventional C_nEO_m type nonionic surfactant systems. The rheological measurements indicate a highly viscoelastic nature of these lyotropic LC phases and disclose a lamellar phase characteristic with a rather strong rigidity at high surfactant concentrations. The control experiment with Brij 97(polyoxyethylene (10) oleyl ether)/[Bmim]BF₄ system and the FTIR measurements help to recognize that the solvophobic interaction combining with the hydrogen bonding are the main driving forces for the LC phases formation.     

Aggregation behavior of long-chain ionic liquids in an ionic liquid

The aggregation behavior of long-chain ionic liquids 1-alkyl-3-methylimidazolium bromide (C(n)mimBr) in another ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), was studied for the first time. Surface tension measurements revealed that aggregates are formed by C(n)mimBr, and freeze fracture transmission electron microscopy (FF-TEM) observations suggested the aggregates are spheres with a size much larger than traditional micelles. The sizes of the aggregates were further confirmed by dynamic light scattering (DLS) measurements.