Microwave Irradiation for the Facile Synthesis of Transition-Metal Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal-Carbonyl Precursors and Ru-, Rh-, and Ir-NP/IL Dispersions as Biphasic Liquid-Liquid Hydrogenation Nanocatalysts for Cyclohexene

Stable chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, and iridium metal nanoparticles (MNPs) have been reproducibly obtained by facile, rapid (3 min), and energysaving 10 W microwave irradiation (MWI) under an argon atmosphere from their metal–carbonyl precursors [Mx(CO)y] in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]). This MWI synthesis is compared to UV-photolytic (1000 W, 15 min) or conventional thermal decomposition (180–2508C, 6–12 h) of [Mx(CO)y] in ILs. The MWIobtained nanoparticles have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long-term stable M-NP/IL dispersions (characterization by transmission electron microscopy (TEM), transmission electron diffraction (TED), and dynamic light scattering (DLS)). The ruthenium, rhodium, or iridium nanoparticle/IL dispersions are highly active
and easily recyclable catalysts for the biphasic liquid–liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 522 (mol product)(mol Ru)1h1 and 884 (mol product)(molRh)1h1 and give almost quantitative conversion within 2 h at 10 bar H2 and 908C. Catalyst poisoning experiments with CS2 (0.05 equiv per Ru) suggest a heterogeneous surface catalysis of RuNPs.

Liquid densities, heat capacities, refractive index and excess quantities for {protic ionic liquids plus water} binary system

Densities, rho, of aqueous solutions of the room temperature protic ionic liquid (PIL), pyrrolidinium nitrate are determined at the atmospheric pressure over the temperature range from (283.15 to 323.15) K and within the whole composition range. The molar isobaric heat capacities, C(p), and refractive index, n(D), of {PIL + water} binary system are measured at 298.15 K. The excess molar volumes V(E), excess molar isobaric heat capacities C(p)(E), and deviation from ideality of refractive index Delta(phi)n, of pyrrolidinium nitrate aqueous solutions were deduced from the experimental results as well as apparent molar volumes V(phi), partial molar volumes (V) over bar (m,i), and thermal expansion coefficients alpha(p). The V(E) values were found to be positive over the entire composition range at all temperatures studied therein, whereas deviations from ideality were negative for refractive index Delta(phi)n. The volumetric properties of binary mixtures containing water and four other protic ionic liquids, such as pyrrolidinium hydrogen sulfate, pyrrolidinium formiate, collidinium formate, and diisopropyl-ethylammonium formate were also determined at 298.15 K. Results have been then discussed in terms of molecular interactions and molecular structures in these binary mixtures. (C) 2009 Elsevier Ltd. All rights reserved.

Evaluation of the ionic liquids 1-alkyl-3-methylimidazolium hexafluorophosphate as a solvent for the extraction of benzene from cyclohexane : ( Liquid + liquid ) equilibria

In the catalytic hydrogenation of benzene to cyclohexane, the separation of unreacted benzene from the product stream is inevitable and essential for an economically viable process. In order to evaluate the separation efficiency of ionic liquids (ILs) as a solvent in this extraction processes, the ternary (liquid + liquid) equilibrium of 1-alkyl-3-methylimidazolium hexafluorophosphate, [Cnmim][PF6] (n = 4, 5, 6), with benzene and cyclohexane was studied at T = 298.15 K and atmospheric pressure. The reliability of the experimentally determined tie-line data was confirmed by applying the Othmer–Tobias equation. The solute distribution coefficient and solvent selectivity for the systems studied were calculated and compared with literature data for other ILs and sulfolane. It turns out that the benzene distribution coefficient increases and solvent selectivity decreases as the length of the cation alkyl chain grows, and the ionic liquids [Cnmim][PF6] proved to be promising solvents for benzene–cyclohexane extractive separation. Finally, an NRTL model was applied to correlate and fit the experimental LLE data for the ternary systems studied.

Use of a rotating disc reactor to investigate the heterogeneously catalysed oxidation of cinnamyl alcohol in toluene and ionic liquids

To evaluate the effect of mass transfer limitations in the three-phase oxidation of cinnamyl alcohol carried out in toluene and an ionic liquid (1-butyl-3-methyl-imidazolium bis(trifluoromethylsulphonyl)imide), studies have been performed in a rotating disc reactor and compared with those carried out in a stirred tank reactor where mass transfer effects are considered negligible. High catalyst efficiencies are found in the stirred tank reactor with the use of both ionic liquid and toluene, although there is a decrease in rate for the ionic liquid reactions. In contrast, internal pore diffusion limits the reaction in both solvents in the rotating disc reactor. This mass transfer resistance reduces the problem of overoxidation of the metal surface when the reaction is carried out in toluene, leading to significantly higher rates of reaction than expected, although at the cost of decreased selectivity.

Predicting physical properties of ionic liquids

A simple method to predict the densities of a range of ionic liquids from their surface tensions, and vice versa, using a surface-tension-weighted molar volume, the parachor, is reported. The parachors of ionic liquids containing 1-alkyl-3-methylimidazolium cations were determined experimentally, but were also calculated directly from their structural compositions using existing parachor contribution data for neutral compounds. The calculated and experimentally determined parachors were remarkably similar, and the latter data were subsequently employed to predict the densities and surface tensions of the investigated ionic liquids. Using a similar approach, the molar refractions of ionic liquids were determined experimentally, as well as calculated using existing molar refraction contribution data for uncharged compounds. The calculated molar refraction data were employed to predict the refractive indices of the ionic liquids from their surface tensions. The errors involved in the refractive index predictions were much higher than the analogous predictions employing the parachor, but nevertheless demonstrated the potential for developing parachor and molar refraction contribution data for ions as tools to predict ionic liquid physical properties.

Molecular dynamics simulation of ionic liquids: The effect of electronic polarizability

An electronically polarizable model has been developed for the ionic liquid 1-ethyl-3-methylimidazolium nitrate (EMIM+/NO3-), Molecular dynamics simulation studies were then performed on both the polarizable and nonpolarizable versions of the model. Comparisons of shear viscosity and diffusion constants at 400 K show that the effects of polarizability are quite substantial and the polarizable model results are in better agreement with the experimental values.

On the structure and dynamics of ionic liquids

The structure and dynamics of the ionic liquid 1-ethyl-3-methylimidazolium nitrate is studied by molecular dynamics simulations. We find long-range spatial correlations between the ions and a three-dimensional local structure that reflects the asymmetry of the cations. The main contribution to the configurational energy comes from the electrostatic interactions which leads to charge-ordering effects. Radial screening and threedimensional distribution of charge are also analyzed. The motion of a single ion is studied via velocity and reorientational correlation functions. It is found that ions "rattle" in a long-lived cage, while the orientational structure relaxes on a time scale longer than 200 ps. As in a supercooled liquid, the mean square displacements reveal a subdiffusive dynamics. In addition, the presence of dynamic heterogeneities can be detected by analyzing the non-Gaussian behavior of the van Hove correlation function and the spatial arrangement of the most mobile ions. The short-time collective dynamics is also studied through the electric current time correlation function.

Simulation of interfaces between room temperature ionic liquids and other liquids

The structure and properties of the interfaces between the room temperature ionic liquid dimethylimidazolium chloride ([dmim]Cl) and different Lennard-Jones fluids and between ionic liquid and water have been studied by molecular dynamics simulations, and compared to the ionic liquid-vapour interface. Two contrasting types of interface were investigated, thermodynamically stable interfaces between ionic liquid and vapour and between ionic liquid and Lennard-Jones fluids, and diffusing interfaces between miscible phases of different compositions involving water. The density profiles of different species through the interface are presented. The cations and water molecules near the former type of interface are aligned relative to the surface, but no orientational preference was found near or in the broad diffusing interface. The ionic liquid has a negative electrostatic potential relative to vapour or Lennard-Jones fluid, but is more positive than pure water. This contrast is explained in terms of the relative importance of orientation and concentration differences in the two types of interface.

Conventional free radical polymerization in room temperature ionic liquids: a green approach to commodity polymers with practical advantages

Free-radical polymerization of methyl methacrylate and styrene using conventional organic initiators in the room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([ C(4)mim][PF6]) is rapid and produces polymers with molecular weights up to 10x higher than from benzene; both polymerization and isolation of products were achieved without using VOCs, offering economic as well as environmental advantages.

Mutual Solubilities of Water and Hydrophobic Ionic Liquids

The ionic nature of ionic liquids (ILs) results in a unique combination of intrinsic properties that produces increasing interest in the research of these fluids as environmentally friendly "neoteric" solvents. One of the main research fields is their exploitation as solvents for liquid-liquid extractions, but although ILs cannot vaporize leading to air pollution, they present non-negligible miscibility with water that may be the cause of some environmental aquatic risks. It is thus important to know the mutual solubilities between ILs and water before their industrial applications. In this work, the mutual solubilities of hydrophobic yet hygroscopic imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based ILs in combination with the anions bis(trifluoromethylsulfonyl)imide, hexafluorophosphate, and tricyanomethane with water were measured between 288.15 and 318.15 K. The effect of the ILs structural combinations, as well as the influence of several factors, namely cation side alkyl chain length, the number of cation substitutions, the cation family, and the anion identity in these mutual solubilities are analyzed and discussed. The hydrophobicity of the anions increases in the order [C(CN)3] <[PF6] <[Tf2N] while the hydrophobicity of the cations increases from [Cnmim] <[Cnmpy] [Cnmpyr] <[Cnmpip] and with the alkyl chain length increase. From experimental measurements of the temperature dependence of ionic liquid solubilities in water, the thermodynamic molar functions of solution, such as Gibbs energy, enthalpy, and entropy at infinite dilution were determined, showing that the solubility of these ILs in water is entropically driven and that the anion solvation at the IL-rich phase controls their solubilities in water. The COSMO-RS, a predictive method based on unimolecular quantum chemistry calculations, was also evaluated for the description of the water-IL binary systems studied, where it showed to be capable of providing an acceptable qualitative agreement with the experimental data.

The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents

The oxidation of hydrogen was studied at an activated platinum micro-electrode by cyclic voltammetry in the following ionic liquids: [C(2)mim][NTf2], [C(4)mim][NTf2], [N-6.2.2.2][NTf2], [P-14.6.6.6][NTf2], [C(4)mim][OTf], [C(4)mim][BF4] [C(4)mim][PF6], [C(4)mim][NO3], [C(6)mim]Cl and [C(6)mim][FAP] (where [C(n)mim](+) = 1-alkyl-3-methylimidazolium, [N-6,N-2,N-2,N-2](+) = n-hexyltriethylammonium, [P-14,P-6,P-6,P-6](+) = tris(n-hexyltetradecyl) phosphonium, [NTf2](-) = bis(trifluoromethylsulfonyl)amide, [OTf] = trifluoromethlysulfonate and [FAP](-) = tris(perfluoroethyl)trifluorophosphate). Activation of the Pt electrode was necessary to obtain reliable and reproducible voltammetry. After activation of the electrode, the H-2 oxidation waves were nearly electrochemically and chemically reversible in [C(n)mim][NTf2] ionic liquids, chemically irreversible in [C(6)mim]Cl and [C(4)mim][NO3], and showed intermediate characteristics in OTf-, [BF4](-), [PF6](-), [FAP](-) and other [NTf2](-)-based ionic liquids. These differences reflect the contrasting interactions of protons with the respective RTIL anions. The oxidation peaks are reported relative to the half-wave potential of the cobaltocenium/cobaltocene redox couple in all ionic liquids studied, giving an indication of the relative proton interactions of each ionic liquid. A preliminary temperature study (ca. 298-333 K) has also been carried out in some of the ionic liquids. Diffusion coefficients and solubilities of hydrogen at 298 K were obtained from potential-step chronoamperometry, and there was no relationship found between the diffusion coefficients and solvent viscosity. RTILs possessing [NTf2](-) and [FAP](-) anions showed the highest micro-electrode peak currents for the oxidation in H-2 saturated solutions, with[C(4)mim][NTf2] toeing the most sensitive. The large number of available RTIL anion/cation pairs allows scope for the possible electrochemical detection of hydrogen gas for use in gas sensor technology. (c) 2008 Elsevier B.V. All rights reserved.

Preparation of AgX (X = Cl, I) nanoparticles using ionic liquids

Nanoparticles of silver halides have been prepared by mixing silver halide powder with a single liquid phase consisting of an ionic liquid, isooctane, n-decanol and water. Much higher nanoparticle concentrations may be formed with ionic liquids using this new simple method than are found with conventionally applied surfactants. This method also emphasizes the applicability of ionic liquids as versatile components in microemulsions and as solvents for the synthesis of nanomaterials. The effect on the nanoparticles of changing the composition of the liquid mixtures and the nature of the ionic liquid is analysed. High nanoparticle concentrations were only found with chloride based ionic liquids, indicating the importance of the ionic liquid anion in the mechanism of the reaction.

Acylation of sulfonamines using silica grafted 1-butyl-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazolium ionic liquids as catalysts

Heterogeneous immobilized ionic liquid catalysts were prepared via grafting of 1,3-dimethyl-3-(3-triethoxysilylpropyl)-imidazolium tetrafluoroborate or bist{(trifluoromethyl)sulfonyl} imide ([NTf2](-)) on silica supports with different surfaces and pore size. In addition to the adsorption-desorption isotherms of nitrogen at -196C, the catalysts were characterized by TG-DTA, XPS, DRIFTS, DR-UV-vis, NMR, and XRD techniques. The catalytic behavior was checked in the acylation of three different sulfonamines: benzenesulfonamine, p-nitrobenzene-sulfonamine, and p-methoxybenzene-sulfonamine with acetic acid, acetic anhydride and maleic anhydride. These tests confirmed the acid Lewis properties of these catalysts. (c) 2007 Elsevier B.V. All rights reserved.

Electroreduction of sulfur dioxide in some room-temperature ionic liquids

The mechanism of sulfur dioxide reduction at a platinum microelectrode was investigated by cyclic voltammetry in several room-temperature ionic liquids (RTILs)-[C(2)mim][NTf2], [C(4)mim][BF4], [C(4)mim][NO3], [C(4)mim][PF6], and [C(6)mim][Cl] where [C(2)mim] is 1-ethyl-3-methylimidazolium, [C(4)mim] is 1-butyl-3-methylimidazolium, [C(6)mim] is 1-hexyl-3-methylimidazolium, and [NTf2] is bis(trifluoromethylsufonyl)imide-with special attention paid to [C(4)mim][NO3] because of the well-defined voltammetry, high solubility, and relatively low diffusion coefficient of SO2 obtained in that ionic liquid. A cathodic peak is observed in all RTILs between -2.0 and -1.0 V versus a silver quasi-reference electrode. In [C(4)mim][NO3], the peak appears at -1.0 V, and potential step chronoamperometry was used to determine that SO2 has a very high solubility of 3100 (+/-450) mM and a diffusion coefficient of 5.0 (+/-0.8) x 10(-10) m(2) s(-1) in that ionic liquid. On the reverse wave, up to four anodic peaks are observed at ca. -0.4, -0.3, -0.2, and 0.2 V in [C(4)mim][NO3]. The cathodic wave is assigned to the reduction of SO2 to its radical anion, SO2-center dot. The peaks at -0.4 and -0.2 V are assigned to the oxidation of unsolvated and solvated SO2-center dot, respectively. The peak appearing at 0.2 V is assigned to the oxidation of either S2O42- or S2O4-center dot. The activation energy for the reduction of SO2 in [C(4)mim][NO3] was measured to be 10 (+/-2) kJ mol(-1) using chronoamperometric data at different temperatures. The stabilizing interaction of the solvent with the reduced species SO2-center dot leads to a different mechanism than that observed in conventional aprotic solvents. The high sensitivity of the system to SO2 also suggests that [C(4)mim][NO3] may be a viable solvent in gas sensing applications.

Structure and solvation in ionic liquids

This Account describes experimental data used to understand the structure of ionic liquids and solute-solvent interactions of both molecular solutes and dissolved metal complexes. In general, the structures of the ionic liquids determined from experimental data show good agreement with both simulated structures and solid-state structures. For all ionic liquids studied, strong charge ordering is found leading to long-range order even in the presence of a solute. For dissolved metal complexes, the ionic liquid is not innocent and a clear dependence on the speciation is observed with variations in both the cation and anion.