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.     

Pressure-Induced Solidification of 1-Butyl-3-methylimidazolium Tetrafluoroborate

We have used Raman spectroscopy to investigate the high-pressure phase behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), a representative ionic liquid, at pressures up to ~7.5 GPa. We have also studied how increasing pressure leads to conformational changes in the [bmim]⁺ cation. We have found that liquid [bmim][BF₄] undergoes pressure-induced solidification (freezing) into a superpressed (metastable) state at 2.5 GPa; another structural change probably occurs at ~6 GPa. Remarkably, conformational changes in the [bmim]⁺ cation between trans and gauche conformers are concordant with the metastable structural changes of [bmim][BF₄]. As the pressure is increased from ambient, the fraction of gauche conformers increases, but the gauche fraction decreases above the solidification pressure (2.5 GPa), and slope of the gauche/trans ratio changes again above 6 GPa. We interpret these results in terms of the fragility of the ionic liquid.     

Highly Efficient Extraction and Oxidative Desulfurization System Using Na7H2LaW10O36⋅32 H2O in [bmim]BF4 at Room Temperature

Highly efficient, deep desulfurization of model oil containing dibenzothiophene (DBT), benzothiophene (BT), or 4,6‐dimethyldibenzothiophene (4,6‐DMDBT) has been achieved under mild conditions by using an extraction and catalytic oxidative desulfurization system (ECODS) in which a lanthanide‐containing polyoxometalate Na₇H₂LnW₁₀O₃₆ ? 32 H₂O (LnW₁₀; Ln=Eu, La) acts as catalyst, [bmim]BF₄ (bmim=1‐butyl‐3‐methylimidazolium) as extractant, and H₂O₂ as oxidant. Sulfur removal follows the order DBT>4,6‐DMDBT>BT at 30 ° C. DBT can be completely oxidized to the corresponding sulfone in 25 min under mild conditions, and the LaW₁₀/[bmim]BF₄ system could be recycled for ten times with only slight decrease in activity. Thus, LaW₁₀ in [bmim]BF₄ is one of the most efficient systems for desulfurization using ionic liquids as extractant reported so far.     

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.     

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.     

1-Butyl-3-methylimidazolium p-toluenesulfinate: a novel reagent for synthesis of sulfones and β-ketosulfones in ionic liquid

A novel task-specific ionic liquid, 1-butyl-3-methylimidazolium p-toluenesulfinate, [bmim][p-TolSO₂] has been synthesized and used as a nucleophile for the reaction with alkyl bromides and phenacyl bromides to prepare sulfones and β-ketosulfones in excellent yields (80-93%) in [bmim][BF₄] ionic liquid. The isolated yields of sulfones and β-ketosulfones were higher in [bmim][BF₄] than other organic solvents at room temperature.     

Cationic ring-opening polymerization of 3,3-bis（chloromethyl）oxacyclobutane in ionic liquids

Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane catalyzed by BF_3·OEt_2 was carried out in ionic liquids [bmim]BF_4 and [bmim]PF_6.The influences of BCMO concentration and molar ratio of BCMO/BF_3·OEt_2 on the molecular weights and yield of PBCMO were investigated.The polymerization in ionic liquids proceed to high conversions,although molecular weights are limited,similar to polymerization in organic solvent such as CH_2Cl_2.Follow a viewpoint of green chemistry, we feel ionic liquid [bmim]BF_4 is superior to [bmim]PF_6.Extracting [bmim]PF_6 from the product using organic solvent as extractant limits its advantage as a green reaction media.     

Oxidation of aromatic aldehydes and ketones by H2O2/CH3ReO3 in ionic liquids: a catalytic efficient reaction to achieve dihydric phenols

A convenient and efficient application of hydrogen peroxide/methyltrioxorhenium in ionic liquids [bmim]BF₄ and [bmim]PF₆ for the oxidation of hydroxylated and methoxylated benzaldehydes and acetophenones to the corresponding phenols is described. Good yields of products were obtained in short reaction times.     

3-exo-tet Cyclization of 2,2-disubstituted 1,3-dihalopropanes with indium in aqueous and ionic liquid solvent system

The 3-exo-tet cyclization of 2,2-disubstituted 1,3-dihalopropanes with In powder in THF solution of 20% H₂O, dioxane solution of 20% H₂O, and ionic liquids, such as [bmim]Br, [bmim]Cl, and [bmin]BF₄, respectively, was efficiently carried out to form the corresponding 1,1-disubstituted cyclopropanes in good yields. The cyclopropanation of 2,2-disubstituted 1,3-dihalopropanes with In powder in ionic liquids, such as [bmim]Br, [bmim]Cl, and [bmin]BF₄, was markedly accelerated compared with that in a THF solution of 20% H₂O and a dioxane solution of 20% H₂O. The mechanism was proposed to involve the radical 3-exo-tet cyclization of the formed 3-halopropyl radical.     

Aggregation behavior of alkyl triphenyl phosphonium bromides in aprotic and protic ionic liquids

The aggregation behavior of alkyltriphenylphonium bromides, C _n TPB (n?=?12 and 14), has been investigated in two different room-temperature ionic liquids (ILs), the aprotic 1-butyl-3-metyllimidazolium tetrafluoroborate ([bmim][BF₄]), and the protic ethylammonium nitrate (EAN). The critical micelle concentration was determined by the surface tension measurements. The calculated thermodynamic parameters based on surface tension measurements at various temperatures indicate that the micellization for C _n TPB in both aprotic [bmim][BF₄] and protic EAN is enthalpy-driven. But stronger solvophobic interactions presented between C _n TPB and protic EAN than aprotic [bmim][BF₄]. ¹H NMR spectra were further conducted to reveal that ethylammonium cation can insert into the micelle while imidazole cation only locates among the head groups of C _n TPB.     

Ionic Liquid Promoted Multicomponent Reaction: A Good Strategy for the Eco‐Compatible Synthesis of Functionalized Pyrroles

Task specific [bmim]BF₄ was found to be reusable, alternative, and effective reaction media for multicomponent synthesis of highly functionalized pyrroles. Generality of the procedure was established by synthesizing various pyrroles from wide range of aromatic/aliphatic amine, phenacyl bromide, and electrophilic alkynes by utilizing this protocol without any acid or metal catalyst. Ecocompatibility, short reaction time, excellent yield, recyclability of [bmim]BF₄, low cost, easy work‐up, and mild reaction conditions are additional advantages of the procedure in the context of sustainable and green chemistry.     

Epoxidation in ionic liquids: A comparison of rhenium(VII) and molybdenum(VI) catalysts

Complexes of the type (dimethyl-bpy)MoO₂Cl₂ and Schiff/Lewis-base complexes of methyltrioxorhenium (MTO), being efficient homogeneous catalysts for the epoxidation of olefins, have been examined with respect to their catalytic performance at 55 and 25 °C in systems employing room temperature ionic liquids (RTILs) of composition [BMIM]NTf₂, [BMIM]PF₆, [BMIM]BF₄ and [C₈MIM]PF₆ as solvents. The performance in the cyclooctene epoxidation was observed to be strongly dependent on the water content of the system and the catalyst solubility in the RTIL. MTO based systems prove to be superior with respect to lower energy consumption, higher stability and higher product yields compared to the investigated Mo(VI) system under the conditions applied.     

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.     

ZnO/MgO containing ZnO nanoparticles as a highly effective heterogeneous base catalyst for the synthesis of 4H-pyrans and coumarins in [bmim]BF4

4H-Pyrans and coumarins were synthesized through one-pot reactions using ZnO/MgO solid sample containing ZnO nanoparticles as an efficient reusable catalyst in ionic liquid, [bmim]BF₄. The catalyst is inexpensive and readily available, stable and storable, easily recycled and reused for several cycles with consistent activity. The procedure offers advantages in terms of high yields, short reaction times, and mild solvent-free reaction conditions.     

Chemoselective reduction of aromatic nitro and azo compounds in ionic liquids using zinc and ammonium salts

Nitroarenes were chemoselectively reduced to the corresponding amines using zinc and aqueous ammonium salts in ionic liquids as a safe and recyclable reaction medium. Our results specify the effect of ammonium salts in the process; the combination of Zn/NH₄Cl in [bmim][PF₆] or Zn/HCO₂NH₄ in [bmim][BF₄] were the suitable conditions for the reduction of nitroarenes. Azobenzenes were also smoothly reduced to hydrazobenzenes with Zn/HCO₂NH₄ (aq.) in recyclable [bmim][BF₄] without any over reduction to the corresponding anilines.     

Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Amine basicity: measurements of ion pair stability in ionic liquid media

The stability constants relevant to the formation of amine/p-nitrophenol ion pairs have been determined in [bmim][BF₄] solution, in the presence of butylamine, piperidine, and triethylamine, by using spectrophotometric measurements. In order to evaluate how the ion pair stability is affected by ionic liquid structure, piperidine has been chosen as model amine for studies in [bmim][PF₆], [bmim][NTf₂], [bm₂im][NTf₂] and in several [bmim][BF₄]/1,4-dioxane binary mixtures. Data obtained in ionic liquid solutions have been compared with those previously reported in conventional organic solvents.     

Investigation on the Complexation of Dioxovanadium (V) with D-(-)-Quinic Acid in Water + 1-Butyl-3-Methylimidazolium Tetrafluoroborate and Water + Methanol Mixed Solvents Using the KAT Model

The complex formation reaction of the $ {\text{VO}}_{2}^{ + } $ VO 2 + cation with D-(-)-quinic acid {(1R,3R,4S,5R)-(-)-1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid} at T = 298 K, I = 0.1 mol·dm^?3 of sodium chloride in various aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF₄, and methanol were studied by using potentiometric and UV spectrophotometric techniques. As far as we know, the calculated stability constants data presented in the current work are the first reported values for [bmim]BF₄ and methanol mixed solvents. The Kamlet–Abboud–Taft solvatochromic equation enabled us to interpret the UV data and the stability constants values. The Redlich–Kister equation was applied for the calculation of solvatochromic parameters in the binary water + [bmim]BF₄ mixtures. Hydrogen bonding is important for the dissociation constant in both media. In these systems the solvent polarizability and hydrogen-bond donor ability are the main interactions for the stability constants in the aqueous ionic liquid and methanol solutions, respectively.     

Ionic Liquid as an Efficient and Recyclable Reaction Medium for the Synthesis of Pyrido[2,3‐d]pyrimidines

Ionic liquid [bmim]BF₄ was found to be an efficient and recyclable reaction medium for the one‐pot synthesis of pyrido[2,3‐d]pyrimidines. The structures of the products were characterized by IR, ¹H NMR, and HRMS spectra. This method had the advantages of easier work‐up, milder reaction conditions, high yields, and environmentally benign procedure.     

Potassium carbonate as a base for the N-alkylation of indole and pyrrole in ionic liquids

The methodology for the N-alkylation of indole and pyrrole using potassium carbonate in 1-n-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF₄] as the sustainable reaction media with acetonitrile as the cosolvent is described herein. Our approach provides good yields with alkyl halides as well as sulfonates as the electrophiles. Cesium carbonate was also found to be a consistent base in the N-alkylation. The proposed methodology is simple and mild with easy workup.