Imidazolium ionic liquids with short polyoxyethylene chains

It has been observed by us earlier that imidazolium ionic liquids ([bmim][BF₄] react with paraformaldehyde giving in nearly quantitative yield imidazolium ionic liquids substituted at 2‐position with hydroxymethyl group ([bhmim][BF₄]). In this article, we describe the application of those ionic liquids (after converting hydroxyl group into alkoxide anion by reaction with sodium hydride) as initiators for anionic polymerization of ethylene oxide (EO). Up to DP_n ～ 30 polymerization proceeds without side reactions, and the product is exclusively low‐molecular‐weight polyoxyethylene containing imidazolium head group (POE‐IL) with DP_n equal to [EO]/[bhmim] ratio. By increasing [EO]/[bhmim] ratio further, side reaction start to interfere, and macromolecules that does not contain imidazolium head groups are also formed, as evidenced by analysis of MALDI TOF spectra. Blending of POE‐IL with high‐molecular‐weight POE leads to significant reduction of crystallinity of POE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6961–6968, 2008     

Solubility of CO2 in imidazolium-based tetrafluoroborate ionic liquids

The solubility of CO₂ in imidazolium ionic liquids (ILs), 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF₄]), 1-hexyl-3-methyl imidazolium tetrafluoroborate ([hmim][BF₄]) and 1-octyl-3-methyl imidazolium tetrtafluoroborate ([omim][BF₄]) was determined at 305-25 K and pressures from 1 to 9 MPa. The influence of chain length of alkyl substituents on the imidazolium cation on the solubility of CO₂ was investigated. The differences in solubility with chain length are in the sequence [omim][BF₄] > [hmim][BF₄] > [bmim][BF₄]. The solubility data were correlated by the extended Henry's law, and enthalpy, Gibbs free energy and entropy changes were obtained.     

Microwave‐assisted ring‐opening polymerization of trimethylene carbonate in the presence of ionic liquid

Microwave‐assisted ring‐opening polymerization (MROP) of trimethylene carbonate in the presence of 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim]BF₄) ionic liquid was investigated. In the presence of 5 wt % [bmim]BF₄, poly (trimethylene carbonate) (PTMC) with a number‐average molar mass (M_n) of 36,400 g/mol was obtained at 5 W for only 60 min. The M_n of PTMC synthesized in the presence of [bmim]BF₄ was much higher than that produced in bulk at the same reaction time. In addition, compared with those produced by conventional heating, the M_n of PTMC and monomer conversion by MROP with or without [bmim]BF₄ were both higher. Thermal properties of the resulting PTMC were characterized by differential scanning calorimetry. Under microwave irradiation in the presence of ionic liquid, the polymerization could be carried out efficiently and effectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5857–5863, 2007     

An effective system to synthesize methanofullerenes: substrate-ionic liquid-ultrasonic irradiation

Dehalogenation of the polyhalides, CHCl₃, C₆₀(CCl₂), CH₂I₂, and 7,7-dibromobicyclo(4,1,0)heptane, by treatment with zinc, magnesium or NaOH powder, followed by the in situ reaction with fullerene in the presence of ultrasonic irradiation and in the ionic liquid solvents, [bmim][PF₄] or [omim][BF₄], provided [6,6]-junction cycloaddition products in 53-79% yields. Only single isomers of the products were detected in the reaction solutions.     

Optical and Bioelectrochemical Characterization of Water‐Miscible Ionic Liquids Based Composites of Multiwalled Carbon Nanotubes

Acidic treated multiwalled carbon nanotubes (AMWNTs) were ground with water‐miscible room temperature ionic liquids, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim]BF₄), and resulted in AMWNTs‐[bmim]BF₄ composite. Its electrical‐ionic conductivity and optical properties were compared with the other two types of carbon materials‐[bmim]BF₄ composites: pyrolytic graphite powder (PGP), pristine multiwalled carbon nanotubes (PMWNTs), through the ac impedance technology and Raman spectroscopy. The impedance data show that AMWNTs‐[bmim]BF₄ composite exhibits the highest conductivity. Raman spectra study exhibits that the [bmim]BF₄ can form gel with PMWNTs and AMWNTs but only form a viscous liquid with PGP. AMWNTs‐[bmim]BF₄ gel modified GC electrode was applied in direct electrochemistry of heme proteins (Hb and HRP) and it catalysis to the reduction of H₂O₂ was investigated.     

Room Temperature Ionic Liquids (RTILs) and Multiwalled Carbon Nanotubes (MWCNTs) as Modifiers for Improvement of Carbon Paste Ion Selective Electrode Response; A Comparison Study with PVC Membrane

Room temperature ionic liquids (RTILs), 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmim]BF₄, and multiwalled carbon nanotubes (MWCNTs) were used for improvement of a praseodymium carbon paste ion selective sensor response. [bmim]BF₄ can be a better binder than mineral oils. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with PVC membrane sensor. The results indicate that potentiometric sensor constructed with ionic liquid shows an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to Pr(III) PVC membrane sensor.     

Influence of ionic liquids on the phase transfer-catalysed enantioselective Michael reaction

The enantioselective Michael addition of dimethyl malonate to 1,3-diphenylprop-2-en-1-one promoted by a quaternary derived ammonium salt from quinine as a phase transfer catalyst in different ionic liquids, 1-butyl-3-methyl imidazolium hexafluorophosphate, [bmim]PF₆, 1-butyl-3-methyl pyridinium tetrafluoroborate, [bpy]BF₄, 1-butyl-3-methyl imidazolium tetrafluoroborate [bmim]BF₄ as well as in conventional organic solvents was studied.     

Direct Electrochemistry and Electrocatalysis of Myoglobin with Ionic Liquid through Multilayers Film on Carbon Ionic Liquid Electrode

Multilayers of myoglobin (Mb) with ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM]BF₄) was assembled on carbon ionic liquid electrode (CILE) based on the electrostatic attraction between the negatively charged Mb and the positively charged imidazolium ion of IL. The CILE was fabricated with 1‐ethyl‐3‐methylimidazolium ethylsulfate ([EMIM]EtOSO₃) as the modifier, which exhibited imidazolium ion on the electrode surface. Then Mb molecules were assembled on the surface of CILE step‐by‐step to get a {IL/Mb}_n multilayer film modified electrode. UV‐Vis adsorption and FT‐IR spectra indicated that Mb remained its native structure in the IL matrix. In deaerated phosphate buffer solution (pH 7.0) a pair of well‐defined quasi‐reversible redox peaks appeared with the apparent formal potential (E^0′) as ‐0.212 V (vs. SCE), which was the characteristic of Mb heme Fe(III)/Fe(II) redox couples. The results indicated that the direct electron transfer of Mb was realized on the modified electrode. The {IL/Mb}_n/CILE displayed excellent electrocatalytic ability to the trichloroacetic acid reduction in the concentration range from 2.0 to 22.0 mmol/L with the detection limit of 0.6 mmol/L (3σ). The proposed method provides a new platform to fabricate the third generation biosensor based on the self‐assembly of redox protein with ILs.     

K2CO3/H2O in [omim][BF4] Ionic Liquid: A Green Medium for Efficient Room‐Temperature Synthesis of N‐Substituted 1,4‐Benzoxazin‐3‐ones

A medium consisting of K₂CO₃ and H₂O in [omim][BF₄] ionic liquid (IL) was used to synthesize N‐substituted 2H‐benzo[b][1,4]oxazin‐3(4H)‐one derivatives from their corresponding o‐aminophenols and 2‐bromoalkanoates. As a result, chemoselective formation of benzoxazinones in high yields has been observed at room temperature. After the reactions and separation of the products, the IL was recovered and successfully reused in subsequent reactions without significant loss of activity.     

Polymerization of phenylacetylene catalysed by RhTp(cod) and RhBp(cod) in ionic liquids: effect of alcohols and of tetraammonium halides

RhTp(cod) ( 1 ) and RhBp(cod) ( 2 ), almost inactive in CH₂Cl₂, became good catalysts of phenylacetylene polymerization in ionic liquids ([bmim]Cl, [bmim]BF₄: bmim = 1‐butyl‐3‐methylimidazolium, [mokt]BF₄: mokt = 1‐methyl‐3‐oktylimidazolium, [bumepy]BF₄: 1‐butyl‐4‐methylpyridinium) and in CH₂Cl₂ in the presence of tetraammonium halides ([R₄N]X, R = Bu, Et; X = Cl, Br). The highest yields of polyphenylacetylene with catalyst 1 were obtained in [bmim]Cl at 65°C (64% after 2 h) and in [mokt]BF₄ at 20°C (56% after 24 h). In alcohols (CH₃OH, (CH₃)₂CHOH, (CH₃)₃COH) as solvents, up to 100% of the polymer was produced. When a mixture of an ionic liquid and CH₃OH was used as the reaction medium, the polymer yield was similar to the yield achieved in an ionic liquid only, but the molecular weight increased remarkably. Tetraammonium salts, [R₄N]X, are co‐catalysts for 1 , and the yield of the polymer increased in the order [Et₄N]Br < [Bu₄N]Br < [Et₄N]Cl < [Bu₄N]Cl. Polymers with molecular weights from 6900 to 38 800 Da were obtained with catalyst 2 in [R₄N]Br or [R₄N]Cl, whereas in ionic liquids ([bmim]Cl, [bmim]BF₄) the corresponding molecular weights were higher, from 51 300 to 60 300 Da. Copyright © 2004 John Wiley & Sons, Ltd.     

An efficient and convenient approach for the synthesis of novel 2‐hydroxy‐12‐aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthene‐11‐ones using p‐toluenesulfonic acid in ethanol and ionic liquid

A novel series of 2‐hydroxy‐12‐aryl‐8,9,10,12‐tetrahydrobenzo[a]xanthene‐11‐ones were synthesized by the one‐pot multicomponent condensation of 2,7‐dihydroxynaphthalene, aromatic aldehydes, and cyclic 1,3‐dicarbonyl compounds in the presence of a catalytic amount of p‐toluenesulfonic acid in ethanol and in ionic liquid butyl methyl imidazolium tetrafluroborate ([bmim]BF₄). The newly developed protocol is operationally convenient, widely applicable, and gives excellent yields of the diversely substituted title compounds in high purity by easy workup. J. Heterocyclic Chem., (2011).     

Effect of imidazolium salts on the catalytic reaction of 1,3-dioxolanes with methyl diazoacetate

Effect of imidazolium salts, [bmim]⁺Cl^?, [bmim]⁺BF₄ ^?, and [bmim]⁺PF₆ ^?, on the reaction of 1,3-dioxolanes with methyl diazoacetate in the presence of copper-containing catalysts was studied. The product composition was found to depend on the reaction conditions and the nature and ratio of components of the catalytic system.     

Influence of 1-alkyl-3-methylimidazolium tetrafluoroborate on the lamellar liquid crystal formed by tetraethylene glycol lauryl ether and water

Lyotropic liquid crystals (LLCs) formed in tetraethylene glycol lauryl ether–water system by the addition of 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _n Mim][BF₄], n?=?2, 4, 6, 8, 10) are characterised by polarised optical microscopy and small-angle X-ray scattering techniques. A small number of [C _n Mim][BF₄] molecules can be solubilised in the liquid crystal without changing the lamellar type. These imidazolium salts are considered as an ideal kind of modifiers for the ordered structure. With different lengths of alkyl chains, [C _n Mim][BF₄] molecules appear in various domains of ordered assemblies: in the water layer for [C₂Mim][BF₄], in the water layer as well as in the polar domain for [C₄Mim][BF₄] and in the apolar domain for the other imidazolium salts with long alkyl chains. Diverse distributions of [C _n Mim][BF₄] molecules in the inner structure bring about their specific influence on the lamellar phase. These results enlighten the use of diverse alkyl-substituted imidazolium salts in modulating LLC and other assemblies and also enrich the aggregation behaviour of these assemblies.     

Palladium‐Catalyzed Enyne Cyclization of 2′‐Alkenyl 2‐Alkynoates in Imidazolium‐Type Ionic Liquids

The use of [bmim][BF₄], [bmim][PF₆], and [bmim][Cl] ILs as the solvents in Pd(II)‐catalyzed enyne cyclization of 2′‐alkenyl 2‐alkynoates in the presence of cupric chloride has been investigated. The Z/E stereoselectivity of the reaction could range from 90:10 to 4:96 by tuning the amount of LiCl in ILs. After the separation of the product, the IL–catalyst mixture could be recovered by treatment with hydrochloric acid and recycled several times without an obvious loss of catalytic activity.     

离子液体中一步合成14-芳基-1,6,7,14-四氢二苯并[a, i]吖啶-1,6-二酮衍生物

室温条件下在离子液体[bmim]BF4中合成了14-芳基-1,6,7,14-四氢二苯并[a, i]吖啶-1,6-二酮类衍生物,该方法具有产率高,反应介质可回收使用,反应底物范围广,反应时间短,操作简单等优点。     

The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures

The density, viscosity and conductivity of ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), 1-octyl-3-methylimidazolium chloride ([omim][Cl]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim] BF4]), 1-hexyl- 3-methylimidazolium chloride ([hmim][Cl]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and the [omim][BF4] + [omim][Cl], [hmim][BF4] + [hmim][Cl], and [hmim][PF6] + [hmim][Cl] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes (VE) of [hmim][BF4] + [hmim][Cl] and [hmim][PF6] + [hmim][Cl] mixtures are positive in the whole composition range. For [omim][BF4] + [omim][Cl], the VE is also positive in the [omim][Cl]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher (VTF) equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.     

One‐Pot Synthesis of Hydroxy Pyrazolo[1,2‐a][1,2,4]triazoles and Their Dehydration Using Recyclable Ionic Liquids as Reaction Media

An eco‐friendly, simple, and efficient one‐pot new procedure has been developed for the synthesis of hydroxy phenylhexahydropyrazolo[1,2‐a][1,2,4]triazoles by condensation of 4‐phenylurazole, aldehydes, and ethyl/methyl acetoacetate using ionic liquid [bmim]BF₄ in presence of l ‐proline at 80°C. The hydroxy pyrazolo[1,2‐a][1,2,4]triazoles could be dehydrated in presence of [bmim]HSO₄ to give corresponding phenyltetrahydropyrazolo[1,2‐a][1,2,4]triazoles in high yields. High yields, less reaction time, operational simplicity, and recyclability of reaction media are the advantages of this protocol.     

Synthesis and Characterisation of Fluorescent Carbon Nanodots Produced in Ionic Liquids by Laser Ablation

Carbon nanodots (C‐dots) with an average size of 1.5 and 3.0 nm were produced by laser ablation in different imidazolium ionic liquids (ILs), namely, 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate (BMI.BF₄), 1‐n‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf₂) and 1‐n‐octyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (OMI.NTf₂). The mean size of the nanoparticles is influenced by the imidazolium alkyl side chain but not by the nature of the anion. However, by varying the anion (BF₄ vs. NTf₂) it was possible to detect a significant modification of the fluorescence properties. The C‐dots are much probably stabilised by an electrostatic layer of the IL and this interaction has played an important role with regard to the formation, stabilisation and photoluminescence properties of the nanodots. A tuneable broadband fluorescence emission from the colloidal suspension was observed under ultraviolet/visible excitation with fluorescence lifetimes fitted by a multi‐exponential decay with average values around 7 ns.     

Synthesis and characterization of anhydrous conducting polyimide/ionic liquid complex membranes via a new route for high‐temperature fuel cells

The paper deals with the synthesis and characterization of a new series of anhydrous conducting acid‐doped complex membranes based on polyimide (PI) and ionic liquid (IL) for high‐temperature fuel cells via a new route. For this purpose, three imidazolium‐based ILs (RIm⁺BF₄^?) with different alkyl chain lengths (R=methyl, ethyl, and butyl) are added into polyamic acid (PAA) intermediate prepared from the reaction of benzophenonetetracarboxylic dianhydride and diaminodiphenylsulfone in different –COOH/imidazolium molar ratios (n = 0.5, 1, and 2). Then, the thermally imidized complex membrane was doped with H₂SO₄. The conductivities of acid‐doped PI/IL complex membranes prepared by taking n of 1 are found to be in the range of 10^?4?10^?5 S cm^?1 at 180°C, whereas the acid‐free PI/IL complex membranes show the conductivity at around 10^?9?10^?10 S cm^?1. Thermogravimetric analysis results reveal that the acid‐doped PI/IL complex membranes are thermally stable up to 250°C. Dynamic mechanical analysis results of the acid‐doped ionically interacted complex membrane show that the mechanical strengths of the PI/IL complex membranes including 1‐methyl imidazolium tetrafluoroborate (MeIm‐BF₄) and 1‐ethyl 3‐methyl imidazolium tetrafluoroborate (EtIm‐BF₄) are comparable with those of pristine PI until 200°C. Furthermore, it can be clearly emphasized that the ionic interaction between carboxylic acid groups of PAA's and IL's cations offers a positive role in long‐term conductivity stability by preventing the IL migration at high temperatures. On the other hand, preliminary methanol permeability tests of the acid‐doped membranes show that they can also be considered as an alternative for direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Pd(OAc)2 catalyzed synthesis of 2-aryl- and 2-heteroaryl-benzoxazoles and benzothiazoles in imidazolium ionic liquids (ILs) without additives and with recycling/reuse of the IL

A facile, high yielding, method for the synthesis of a library of 2-aryl- and 2-heteroaryl-benzoxazoles and benzothiazoles from readily available Schiff bases is reported employing catalytic amounts of Pd(OAc)₂ in imidazolium ionic liquids (bmim)BF₄ and (bmim)PF₆ without ligands and/or additives. Simple product isolation and recycling/re-use of the IL are additional advantages of this method.