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The ionic liquid literature has grown at a remarkable rate since 1998, making it increasingly difficult to assess the important research directions and the underlying, fundamental understanding of ionic liquids. This review is an attempt to examine the facts behind this publication phenomenon, to reveal both the advantages and disadvantages of huge publication rates, and to warn against the dangers of rampant and rapid publication – caveat emptor.

The greenness, or lack thereof, of various ionic liquid syntheses and purification methodologies are assessed using a common tool used in strategic planning viz. strengths weaknesses opportunities threats (SWOT) analysis, including their adherence to the twelve principles of green chemistry, % atom economies and E-factors.

The objective of this work was to study the influence of changing the cation of the ionic liquid (IL) on gas solubility. For this purpose, the low-pressure solubility of carbon dioxide and of ethane in three ILs based on the bis{(trifluoromethyl)sulfonyl}imide anion ([NTf2](-)) was determined experimentally. Solubility data is reported for 1-ethyl-3-methylimidazolium ([C(1)C(2)Im](+)), 1-butyl-1-methylpyrrolidinium ([C(1)C(4)pyrr](+)) and propylcholinium ([N1132-OH](+)) bis{(trifluoromethyl)sulfonyl}imide ILs between 300 and 345 K. These data are precise to within +/- 1% and accurate to within +/- 5%. In these ILs, carbon dioxide (mole fraction solubility between 1 and 3 x 10(-2), molarity between 0.03 and 0.1 mol L-1) is one order of magnitude more soluble than ethane. The effect of changing the cation is small but significant. Changing the cation has a similar effect on both gases even if the differences are more pronounced in the case of ethane with the order of solubility [C(1)C(4)pyrr][NTf2] > [C(1)C(2)Im][NTf2] > [N1132-OH][NTf2]. For all the systems, the solubility decreases with temperature corresponding to exothermic processes of solvation and negative enthalpies and entropies of solvation were calculated. The properties of solvation of the two gases in [C(1)C(4)pyrr][NTf2] do not vary significantly with temperature while important variations are depicted for both gases in [C(1)C(2)Im][NTf2]. (c) 2007 Elsevier B.V. All rights reserved.

The determination of chloride impurities in ionic liquids using ion chromatography is described. A wide range of cation-anion combinations may be analyzed using ion chromatography, including water-immiscible ionic liquids. For all ionic liquids studied, the limit of quantification for chloride was found to be below 8 ppm.

Controlled, multimode microwave irradiation has been employed in a generic solvent-free process to prepare a wide range of ionic liquids based on nitrogen-containing heterocycles. The developed method offers a flexible, small to large-scale approach to prepare ionic liquids, in either sealed or open vessels, in a faster and greener process than any previously described.

Fischer-type (alkoxy)azolyl carbene complexes and Ofele–Lappert-type azolylinylidene complexes were synthesised by reaction of 1-phenylpyrazol-3-yllithium, 4-methylthiazol-2-yllithium, benzothiazol-2-yllithium, 1-methylimidazol-2-yllithium with M(CO)5L (L=CO, THF or Cl−; M=Cr, Mo or W) and subsequent alkylation with CF3SO3CH3. The alkylation of Fischer-type carbene complexes containing an azolyl as the organic substituent proceeded via ring opening of tetrahydrofuran. When the alkylation is carried out in THF, the carbocation CH3O(CH2)4+ acts as an electrophile. Protonation rather than alkylation of coordinated imidazolyl furnished cyclic imine complexes. Changing the donor atom of a coordinated thiazole from N to C by deprotonation and alkylation afforded a carbene complex.

The sections in this article are The Status Quo of Green Ionic Liquid Syntheses Ionic Liquid Preparations Evaluated for Greenness Which Principles of Green Chemistry are Relevant to Ionic Liquid Preparations? Atom Economy and the E-factor Atom Economy The E-factor Strengths, Weaknesses, Opportunities, Threats (SWOT) Analyses Conductive Heating Preparation of 1-Alkyl-3-methylimidazolium Halide Salts Purification of 1-Alkyl-3-methylimidazolium Halide Salts SWOT Analysis: Conductively Heated Preparation of 1-Alkyl-3-Methylimidazolium Halide Salts and Their Subsequent Purification Ionic Liquid Syntheses Promoted by Microwave Irradiation Microwave-assisted Versus Traditional Ionic Liquid Preparations SWOT Analysis: Microwave-promoted Syntheses of Ionic Liquids Syntheses of Ionic Liquids Promoted by Ultrasonic Irradiation SWOT Analysis: Ultrasound-promoted Syntheses of Ionic Liquids Simultaneous Use of Microwave and Ultrasonic Irradiation to Prepare Ionic Liquids SWOT Analysis: Simultaneous Use of Microwave and Ultrasonic Irradiation to Prepare Ionic Liquids Preparation of Ionic Liquids Using Microreactors SWOT Analysis: Preparation of Ionic Liquids Using Microreactors Purification of Ionic Liquids with Non-halide Anions Purification of Hydrophobic Versus Hydrophilic Ionic Liquids SWOT Analyses: Purification of Hydrophobic and Hydrophilic Ionic Liquids Decolorization of Ionic Liquids SWOT Analysis: Decolorization of Ionic Liquids Conclusion Acknowledgments Keywords: ionic liquids; synthesis; SWOT analysis; green chemistry

The sections in this article are The Status Quo of Green Ionic Liquid Syntheses Ionic Liquid Preparations Evaluated for Greenness Which Principles of Green Chemistry are Relevant to Ionic Liquid Preparations? Atom Economy and the E-factor Atom Economy The E-factor Strengths, Weaknesses, Opportunities, Threats (SWOT) Analyses Conductive Heating Preparation of 1-Alkyl-3-methylimidazolium Halide Salts Purification of 1-Alkyl-3-methylimidazolium Halide Salts SWOT Analysis: Conductively Heated Preparation of 1-Alkyl-3-Methylimidazolium Halide Salts and Their Subsequent Purification Ionic Liquid Syntheses Promoted by Microwave Irradiation Microwave-assisted Versus Traditional Ionic Liquid Preparations SWOT Analysis: Microwave-promoted Syntheses of Ionic Liquids Syntheses of Ionic Liquids Promoted by Ultrasonic Irradiation SWOT Analysis: Ultrasound-promoted Syntheses of Ionic Liquids Simultaneous Use of Microwave and Ultrasonic Irradiation to Prepare Ionic Liquids SWOT Analysis: Simultaneous Use of Microwave and Ultrasonic Irradiation to Prepare Ionic Liquids Preparation of Ionic Liquids Using Microreactors SWOT Analysis: Preparation of Ionic Liquids Using Microreactors Purification of Ionic Liquids with Non-halide Anions Purification of Hydrophobic Versus Hydrophilic Ionic Liquids SWOT Analyses: Purification of Hydrophobic and Hydrophilic Ionic Liquids Decolorization of Ionic Liquids SWOT Analysis: Decolorization of Ionic Liquids Conclusion Acknowledgments Keywords: ionic liquids; synthesis; SWOT analysis; green chemistry

Neural network models have been explored for the prediction of the liquid–liquid equilibrium data and aromatic/aliphatic selectivity values. Four ternary systems composed of toluene, heptane, and the ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate, or 1,3-dimethylimidazolium methylsulfate were investigated at 313.2 and 348.2 K.

Neutron diffraction has been used to investigate the structure of liquid mixtures of 1,3-dimethylimidazolium hexafluorophosphate with benzene. Two concentrations of benzene were investigated, namely, 33 mol % and 67 mol %, and show similar structures in each case. The presence of benzene significantly alters the ionic liquid structure, in particular, in the cation-cation interactions, in agreement with the single-crystal structure described recently (Holbrey, J. D.; Reichert, W. M.; Nieuwenhuyzen, M.; Sheppard, O.; Hardacre, C.; Rogers, R. D. Chem. Commun. 2003, 476). In each case, the data was analyzed using an empirical potential structure refinement process.

Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2 calculations. The previously reported anti and gauche forms of the [C4mim]+ cation have been observed, and this study reveals this to be a general feature of the long-chain 1-alkyl derivatives. Analysis of mixtures of [C6mim]Cl and [C6mim][PF6] 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.

The electrochemistry of the salts, [emim]2[UBr6] and [emim]2[UO2Br4] ([emim] = 1-ethyl-3-methylimidazolium), has been investigated in both a basic and an acidic bromoaluminate(III) ionic liquid. In the basic ionic liquid, the hexabromo salt undergoes a one-electron reversible reduction process at a stationary glassy carbon disc electrode, while the tetrabromodioxo salt was reduced to a uranium(IV) species by an irreversible two-electron process with the simultaneous transfer of oxide to the ionic liquid. On the other hand, dissolution of either of the salts in an acidic bromoaluminate(III) ionic liquid resulted in the formation of the same electroactive species. The solid state structures of the uranium chloride salts, [emim]2[UCl6] and [emim]2[UO2Cl4], have previously been reported, but have now been re-evaluated using a new statistical model developed in our group, to determine the presence or absence of weak hydrogen bonding interactions in the crystalline state.

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The effect of the addition of acetonitrile on the solubility of carbon dioxide in an ionic liquid, the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C2mim][NTf2], was studied experimentally at pressures close to atmospheric and as a function of temperature between 290 and 335 K. It was observed that the solubility of carbon dioxide decreases linearly with the mole fraction of acetonitrile from a value of 2.6 × 10-2 in the pure ionic liquid at 303 K to a mole fraction of 1.3 × 10-2 in the mixture [C2mim][NTf2] + CH3CN with xCH3CN = 0.77 at the same temperature. The gas solubility decreases with temperature, and the thermodynamic properties of solvation could be calculated. The vapor pressures of the [C2mim][NTf2] + CH3CN mixtures were measured in the same temperature range, and strong negative deviations from Raoult's law were obtained: up to 36% for a mixture with xCH3CN = 0.46 at 334 K. Negative excess molar volumes of approximately −1 cm3 mol-1 at equimolar composition could also be ...

Neutron diffraction has been used to determine the liquid structure of 1,3-dimethylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([dmim][NTf2]). Significantly smaller charge ordering is found in this liquid compared with analogous chloride and hexafluorophosphate salts due to the diffuse charge density and size of the [NTf2]- anion. This is manifested in a much larger cation-cation and cation-anion separation and an overlap of the cation-cation and cation-anion shells. Comparison of the liquid structure with the crystal structure reported by Holbrey et al. (Dalton Trans. 2004, 2267) indicates little correlation, for example, the [NTf2]- anion adopts a trans orientation predominantly in the liquid whereas a cis orientation is found in the solid phase.

A series of palladium, platinum and manganese di(organo)carbene complexes have been prepared from 4-chloro-N-methylquinolinone by processes that involve alkylation before or after attachment to the metal unit; the nucleophilic heteroatoms are separated from the C-donor atom by three bonds.

The molar polarisability and molar volume for 71 ionic liquids were extracted from 157 measurements of their refractive index and density, which were then further deconstructed into atomic contributions by means of a Designed Regression analysis. Using this approach, the density and refractive index for any chosen ionic liquid with alkyl-substituted imidazolium cations can be predicted in good agreement with experimental data.

Refractive index determination of minerals and gems often requires their immersion in fluids with the same refractive index. However, these natural materials frequently have refractive indices above the ranges of common organic solvents. Most available high refractive index immersion materials are solid at room temperature, toxic, noxious, corrosive, carcinogenic, or any combination thereof. Since the physical properties of ionic liquids can be tuned by varying the cation and/or anion, we have developed immersion fluids for mineralogical studies which are relatively benign. We report here the syntheses of a range of ionic liquids (many novel) based on the 1-alkyl-3-methylimidazolium cation, which all have refractive indices greater than 1.4, and can be used as immersion fluids for optical mineralogy studies. We further show that for a series of ionic liquids with the same anion, the refractive indices can be adjusted by systematic changes in the cation.