A remarkable effect of ionic liquids in transition-metal-free aerobic oxidation of benzylic alcohols

The transition-metal-free aerobic oxidation of benzylic alcohols is uniquely accelerated by a 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF₆)/PhCF₃ biphasic system and Cs₂CO₃ to afford the corresponding ketones in good yields. The reaction system is also applicable to an oxidative cross-esterification of primary benzyl alcohols with a higher aliphatic alcohol.     

Fabrication of gold nano- and microstructures in ionic liquids--a remarkable anion effect

Gold nano- and microstructures such as polyhedral crystals, large single-crystalline nanoplates, hollow trapeziform crystals, holey polyhedra, and dendrites were produced via microwave heating of HAuCl(4).4H(2)O in a variety of ionic liquids (ILs) in the absence of capping agents (polymers or surfactants) or additional reducing agents. The influence of the IL anions and cations on the topology (size, shape, etc.) of gold materials was studied in detail. The anions of the ILs control the topology of materials, whereas the cations used in the experiments exert less influence. It was also found that the HAuCl(4) concentration, reaction temperature, and heating method are key parameters that help to control the topological structures of the gold materials. For example, the thickness of the large single-crystalline nanoplates could be adjusted from 16 to 320 nm by varying the HAuCl(4) concentration and reaction temperature. This easy synthetic approach to gold nano- and microstructures is a seedless, one-step, fast, template-free route that shows good reproducibility and may be further developed to produce other types of metal nanostructures that satisfy specific applications.     

Exceptional efficiency of palladium nanoparticle catalyzed Heck cross-coupling in binary task specific ionic liquids

The utilization of the task specific onium salt supported substrates in ionic liquids as solvents (i.e., binary task specific ionic liquids) for palladium nanoparticle catalyzed Heck cross-coupling reactions is presented. Adequate substrates have been prepared and used leading to expected products in very high yields. Exceptionally high turnover (TON = 940,000, TOF = 208,000) can be achieved taking advantages of this combination. Additional advantages of this technology reside in the monitoring of the reaction and purification of products after degrafting which are simplified to the extreme.     

A new fluorinated anion for room-temperature ionic liquids

A new room-temperature ionic liquid (RTIL) consisting of the fluorinated anion bis(trifluoromethyl)-phosphinate((CF₃)₂PO₂⁻) coupled with the 1-butyl-3-methyl-imidazoliuim (BMIM) cation has been synthesized and characterized by physicochemical and electrochemical means including differential scanning calorimetry (DSC), thermogravimetric analysis, viscosity, conductivity and cyclic voltammetry measurements. Properties are compared with those of the known RTIL consisting of BMIM coupled with the bis(trifluoromethyl)-sulfonylimide (TFSI) anion.     

Novel biocompatible ionic liquids based on gluconate anion

A sustainable organic synthetic methodology for the preparation of novel biocompatible ionic liquids (ILs) based on gluconate anion has been developed. Four functionalized methylimidazolium cations were efficiently combined with gluconic acid by acid-base neutralization reactions. All salts were obtained as RTILs in high yields (92–98%) and in high purity levels. Proton Nuclear Magnetic Resonance (¹H NMR) studies had proved the correct cation/anion proportion (1:1) and their chemical stability. These novel gluconate ILs can be applied for chemistry, material science, and medicine areas.     

First correlation of nanoparticle size-dependent formation with the ionic liquid anion molecular volume

Stable silver nanoparticles are obtained reproducibly by hydrogen reduction of different inorganic precursors from AgIX salts (X = BF4, PF6, OTf) dissolved in the ionic liquids BMim+BF4-, BMim+PF6-, BMim+OTf-, or BtMA+NTf2- [BMim+ = n-butylmethylimidazolium, BtMA+ = n-butyltrimethylammonium, NTf2 = N(O2SCF3)2, and OTf = O3SCF3] in the presence of n-butylimidazole (Bim) as the scavenger for the HX acid byproduct and with a narrow size distribution in the diameter range of 2.8-26.1 nm, which increases linearly with the molecular volume of the ionic liquid anion (transmission electron microscopy characterization).     

Palladium-catalyzed heck arylations of allyl alcohols in ionic liquids: remarkable base effect on the selectivity

Pd-catalyzed Heck arylation of allyl alcohols in tetraalkylammonium ionic liquids (ILs) can be made highly selective toward the formation of either aromatic carbonyl compounds or aromatic conjugated alcohols by carefully choosing both the IL and the base.     

Alkylation of ambident indole anion in ionic liquids

Alkylation of indole salts in different ionic liquids is reported. Ionic liquids increase the alkylation reaction rate of ambident indole anion and reduce the effects of counter ions and/or additives, the alkylation reaction rates being independent of the presence of small amounts of protic solvents or water.      

Reaction between diiodide anion radicals in ionic liquids

Photodetachment of electrons from iodide ions produced diiodide anion radicals in ionic liquids containing ammonium, pyrrolidinium, and piperidinium cations. The rates of reaction between diiodide anion radicals in molecular solvents such as H2O, methanol, and ethanol could be estimated by the Debye-Smoluchowski equation, which accounts for electrostatic interactions using dielectric constants for the molecular solvents. In contrast, the rates of reaction between diiodide anion radicals in the ionic liquids were close to the diffusion-limited rates for the neutral molecules, suggesting that electrostatic repulsion between the diiodide anion radicals is weakened by Coulombic shielding in the ionic liquids.     

A convenient synthesis of triflate anion ionic liquids and their properties

A solvent- and halogen-free synthesis of high purity triflate ionic liquids via direct alkylation of organic bases (amines, phosphines or heterocyclic compounds) with methyl and ethyl trifluoromethanesulfonate (methyl and ethyl triflate) has been developed. Cheap and non-toxic dimethyl and diethyl carbonate serve as source for the methyl and ethyl groups in the preparation of methyl and ethyl triflate by this invented process. The properties of ionic liquids containing the triflate anion are determined and discussed.     

DOSY technique applied to palladium nanoparticles in ionic liquids

Multinuclear ((1)H, (31)P, (19)F and (11)B) diffusion ordered spectroscopy (DOSY) technique has been applied to palladium nanoparticles systems dispersed in ionic liquids (ILs). Even if the nanoparticles themselves cannot be detected through NMR, observation of the solvent (methanol) and the IL ([BMI][PF(6)] or [BMI][NTf(2)]), their diffusion coefficients and their changes in the presence of nanoparticles allow us to draw significant assumptions about the organisation of palladium nanoparticles in the IL. For comparison, the corresponding molecular precursors ([PdCl(2)(cod)] or [Pd(2)(dba)(3)]) have been also studied.     

Safe and fast tetrazole formation in ionic liquids

The [2+3] cycloaddition of nitriles and azides is reliable for intramolecular reactions, but the hazards with volatile azides in intermolecular reactions are tremendous. Zinc catalysis in aqueous solution is a magnificent improvement, but requires the removal of the zinc salts from the acidic product. Herein, we report safe solvents featuring low vapor pressure and good solubility of NaN₃. Ionic liquids based on alkylated imidazoles combined with microwave heating turned out to be a solution for the given tasks.     

The effect of the anion on the physical properties of trihalide-based N,N-dialkylimidazolium ionic liquids

Low viscosity, high density trihalide-based 1-n-butyl-3-methylimidazolium ionic liquids have been prepared and characterised. Key physical properties (density, conductivity, melting point, refractive index, surface tension and diffusion coefficient) of the ionic liquids have been determined and are compared with those of other 1,3-dialkylimidazolium molten salts. The relationship between anion identity and the physical properties of the ionic liquids under investigation is discussed.     

Imidazolium-based ionic liquids formed with dicyanamide anion: influence of cationic structure on ionic conductivity

Ionic liquids composed of dicyanamide anion and various imidazolium-based cations were prepared, and the influence of structural variations such as substituting a hydrogen at 2-position and changing the sort of alkyl group at 1-position of imidazolium cations on their thermal behavior, density, solvatochromic effects, viscosity, ionic conductivity, and surface tension was characterized. The substitution of the 2-hydrogen for methyl group or N-methylimidazole decreases the fluidity and ionic conductivity, mainly caused by the increased cohesive energy associated with the increasing cation size. Chain branching at 1-position also gives rise to the pronounced depression of the fluidity and ionic conductivity, presumably as a consequence of the increased pi-pi interactions between imidazolium rings. We found that the surface tension of the present ionic liquids is in inverse proportion to the molar concentration, which can be originally rationalized on the basis of the hole theory.     

Surface tensions of imidazolium based ionic liquids: anion, cation, temperature and water effect

This work addresses the experimental measurements of the surface tension of eight imidazolium based ionic liquids (ILs) and their dependence with the temperature (288-353 K) and water content. The set of selected ionic liquids was chosen to provide a comprehensive study of the influence of the cation alkyl chain length, the number of cation substitutions and the anion on the properties under study. The influence of water content in the surface tension was studied for several ILs as a function of the temperature as well as a function of water mole fraction, for the most hydrophobic IL investigated, [omim][PF(6)], and one of the more hygroscopic IL, [bmim][PF(6)]. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values.     

Self-aggregation of nonionic surfactants in imidazolium-based ionic liquids with trifluoromethanesulfonate anion

Self-aggregation of polyoxyethylene (POE)-type nonionic surfactants in ionic liquids, 1-butyl- and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (bmimCF₃SO₃ and emimCF₃SO₃), was investigated by means of ¹H-NMR chemical shift, dynamic light-scattering (DLS), and surface tension measurements. The surfactants showed no definite aggregate formation in bmimCF₃SO₃. This shows a remarkable contrast to the previous observation in bmimBF₄ and bmimPF₆, and demonstrates an importance of anion species to determine the property of ionic liquids as a solvent to support the self-assembly of amphiphilic compounds. On the other hand, the surfactants formed micelles in emimCF₃SO₃, which shows an importance of alkyl chain attached to imidazolium ring to determine the solvophobic interaction between surfactant hydrocarbon chains in imidazolium-based ionic liquids. The low solvophobicity of the surfactants to the ionic liquid composed of imidazolium cation with long alkyl chain is attributed to an affinity of the surfactant hydrocarbon chain to the imidazolium alkyl chain. The values of micellization parameters and surface adsorption parameters obtained for the surfactant solutions in emimCF₃SO₃ are reported.     

Surfactant solvation effects and micelle formation in ionic liquids

The formation of micelles in 1-butyl-3-methyl imidazolium chloride (BMIM-Cl) and hexafluorophosphate (BMIM-PF6) were explored using different surfactants and the solvation behavior of the new micellar-ionic liquid solutions examined using inverse gas chromatography.     

Nanostructural organization and anion effects on the temperature dependence of the optical Kerr effect spectra of ionic liquids

The intermolecular spectra of three imidazolium ionic liquids were studied as a function of temperature by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids comprise the 1,3-pentylmethylimidazolium cation ([C(5)mim]+), and the anions, bromide (Br-), hexafluorophosphate (PF(6)-), and bis(trifluoromethanesulfonyl)imide (NTf(2)-). Whereas the optical Kerr effect (OKE) spectrum of [C(5)mim][NTf(2)] is temperature-dependent, the OKE spectra of [C(5)mim]Br and [C(5)mim][PF6] are temperature-independent. These results are surprising in light of the fact that the bulk densities of these room temperature ionic liquids (RTILs) are temperature-dependent. The temperature independence of the OKE spectra and the temperature dependence of the bulk density in [C(5)mim]Br and [C(5)mim][PF(6)] suggest that there are inhomogeneities in the densities of these liquids. The existence of density inhomogeneities is consistent with recent molecular dynamics simulations that show RTILs to be nanostructurally organized with nonpolar regions arising from clustering of the alkyl chains and ionic networks arising from charge ordering of the anions and imidazolium rings of the cations. Differences in the temperature dependences of the OKE spectra are rationalized on the basis of the degree of charge ordering in the polar regions of the RTILs.