Improving carbon dioxide solubility in ionic liquids

Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubility in a number of ionic liquids with systematic increases in fluorination. We also studied nonfluorinated ionic liquids that have structural features known to improve CO2 solubility in other compounds such as polymers, for example, carbonyl groups and long alkyl chains with branching or ether linkages. Results show that ionic liquids containing increased fluoroalkyl chains on either the cation or anion do improve CO2 solubility when compared to less fluorinated ionic liquids previously studied. It was also found that it was possible to obtain similar, high levels of CO2 solubility in nonfluorous ionic liquids. In agreement with our previous results, we found that the anion frequently plays a key role in determining CO2 solubility in ionic liquids.     

Rhodium nanoparticles stabilized by ionic copolymers in ionic liquids: long lifetime nanocluster catalysts for benzene hydrogenation

Novel ionic liquid-soluble ionic copolymers containing imidazolium ionic liquidlike units have been synthesized. Rhodium nanoparticles stabilized by the ionic copolymer in ionic liquids have been successfully obtained. The nanoparticles showed unprecedented lifetime and activity in arene hydrogenation under forcing conditions (a temperature of 75 degrees C and a hydrogen pressure of 40 bar) with a total turnover (TTO) of 20 000 (in five total recycles of 4000 TTOs each) and a turnover frequency of 250 h-1, demonstrating that the combination of ionic liquids with ionic liquidlike stabilizers is a pathway towards highly stable and active nanoparticle catalysts.     

Supported ionic liquid catalysis--a new concept for homogeneous hydroformylation catalysis

The new concept of supported ionic liquid catalysis involves the surface of a support material that is modified with a monolayer of covalently attached ionic liquid fragments. Treatment of this surface with additional ionic liquid results in the formation of a multiple layer of free ionic liquid on the support. These layers serve as the reaction phase in which a homogeneous hydroformylation catalyst was dissolved. Supported ionic liquid catalysis combines the advantages of ionic liquid media with solid support materials which enables the application of fixed-bed technology and the usage of significantly reduced amounts of the ionic liquid. The concept of supported ionic liquid catalysis has successfully been used for hydroformylation reactions and can be further expanded into other areas of catalysis.     

磁性离子液体的应用研究

磁性离子液体是指能够吸附在磁铁上,在外加磁场作用下具有一定磁化强度的离子液体。本文综述了自2004年磁性离子液体概念提出至今在各领域的应用,其可以催化吡咯、3-甲基噻吩等单体合成导电高分子纳米微球,同时起到溶剂和模板的作用;还可以通过外加磁场调整产物的微观结构和形貌,从而得到不同的纳米结构;它也可以充当Lewis酸催化剂,催化傅克反应等一系列化学反应,并可以回收重复使用,而且回收有望通过磁场简单实现;与碳纳米管以共价键结合可以制备具有磁性的碳纳米管。除此之外,磁性离子液体在光控顺磁性超分子体系、吸收有机挥发物等领域的应用在近年也陆续有报道。     

色谱分析中离子液体的应用及其测定

离子液体作为一种优良的溶剂越来越受到人们的关注。由于离子液体特殊的物理化学性质使其在色谱分析中也得到了较广泛的应用。本文综述了离子液体在气相色谱、高效液相色谱和毛细管电泳中的应用,其中包括离子液体作为气相色谱的固定相、高效液相色谱的固定相及流动相添加剂和毛细管电泳的电解质添加剂等,并对离子液体的色谱分离检测作了详细介绍。     

Porous ionic liquids: synthesis and application

Solidification of fluidic ionic liquids into porous materials yields porous ionic networks that combine the unique characteristics of ionic liquids with the common features of polymers and porous materials. This minireview reports the most recent advances in the design of porous ionic liquids. A summary of the synthesis of ordered and disordered porous ionic liquid-based nanoparticles or membranes with or without templates is provided, together with the new concept of room temperature porous ionic liquids. As a versatile platform for functional materials, porous ionic liquids have shown widespread applications in catalysis, adsorption, sensing, actuation, etc. This new research direction towards ionic liquids chemistry is still in its early stages but has great potential.     

The impact of ionic strength and background electrolyte on pH measurements in metal ion adsorption experiments

Our understanding of metal ion adsorption to clay minerals has progressed significantly over the past several decades, and theories have been promulgated to describe and predict the impacts of pH, ionic strength, and background solution composition on the extent of adsorption. Studies evaluating the effects of ionic strength on adsorption typically employ a broad range of background electrolyte concentrations. Measurement of pH in these systems can be inaccurate when pH values are measured with liquid junction pH probes calibrated with standard buffers due to changes in the liquid junction potential between standard, low ionic strength (0.05 M) buffers and high ionic strength solutions (>0.1 M). The objective of this research is to determine the extent of the error in pH values measured at high ionic strength, and to develop an approach for accurately measuring pH over a range of ionic strengths using a combined pH electrode. To achieve this objective, the adsorption of cobalt (10(-5) M) onto gibbsite (10 g/L) from various electrolyte solutions (0.01-1 M) was studied. The pH measurements were determined from calibrations with standard buffers and ionic strength corrected buffer calibrations. The results show a significant effect of the aqueous solution background electrolyte anion and ionic strength on pH measurement. The 0.5 and 1 M ionic strength metal ion adsorption edges shifted to lower pH with increasing ionic strength when pH was calibrated with standard buffers whereas no shift in the adsorption edges was observed when calibrated with ionic strength corrected buffers. Therefore, to obtain an accurate pH measurement, pH calibration should contain the same electrolyte and ionic strength as the samples.     

Poly(ethylene glycol)-lipase complexes that are highly active and enantioselective in ionic liquids

Lipase-catalyzed alcoholysis between vinyl acetate and 2-phenyl-1-propanol was investigated in dialkylimidazolium-based ionic liquids. Although native lipase powder exhibited very low activity in an ionic liquid, forming a poly(ethylene glycol)(PEG)-lipase complex improved the lipase activity in the ionic liquid. The activity of the PEG-lipase complex was higher in ionic liquids than in common organic solvents (n-hexane, isooctane and dimethylsulfoxide). Fluorescence measurements using 4-aminophthalimide revealed that the ionic liquids were more hydrophilic than the organic solvents used for non-aqueous enzymology. A kinetic study of lipase-catalyzed alcoholysis in an ionic liquid ([Bmim][PF6]) revealed that the Michaelis constant (Km) for 2-phenyl-1-propanol in the ionic liquid was half that in n-hexane, suggesting that the ionic liquid stabilized the enzyme-substrate complex. Finally, we carried out enantioselective alcoholysis of 1-phenylethanol in ionic liquids employing the PEG-lipase complex, and obtained high enantioselectivity, comparable to that in n-hexane.     

Picosecond time-resolved fluorescence study on solute-solvent interaction of 2-aminoquinoline in room-temperature ionic liquids: aromaticity of imidazolium-based ionic liquids

Time-resolved fluorescence spectra and fluorescence anisotropy decay of 2-aminoquinoline (2AQ) have been measured in eight room-temperature ionic liquids, including five imidazolium-based aromatic ionic liquids and three nonaromatic ionic liquids. The same experiments have also been carried out in several ordinary molecular liquids for comparison. The observed time-resolved fluorescence spectra indicate the formation of pi-pi aromatic complexes of 2AQ in some of the aromatic ionic liquids but not in the nonaromatic ionic liquids. The fluorescence anisotropy decay data show unusually slow rotational diffusion of 2AQ in the aromatic ionic liquids, suggesting the formation of solute-solvent complexes. The probe 2AQ molecule is likely to be incorporated in the possible local structure of ionic liquids, and hence the anisotropy decays only through the rotation of the whole local structure, making the apparent rotational diffusion of 2AQ slow. The rotational diffusion time decreases rapidly by adding a small amount of acetonitrile to the solution. This observation is interpreted in terms of the local structure formation in the aromatic ionic liquids and its destruction by acetonitrile. No unusual behavior upon addition of acetonitrile has been found for the nonaromatic ionic liquids. It is argued that the aromaticity of the imidazolium cation plays a key role in the local structure formation in imidazolium-based ionic liquids.     

A nearly complete system of average crystallographic ionic radii and its use for determining ionization potentials

Available systems of empirical (crystallographic) ionic radii are compared. All these systems turn out to be compatible if the O^2? radius is taken to be 0.140 nm. The choice of the oxygen ionic radius is dictated by the equality of the metal ion-oxygen ion distances in oxide crystals and the metal ion-oxygen atom distances in crystal hydrates and concentrated aqueous solutions. In all systems of empirical ionic radii under consideration, the uncertainty of determination of ionic radii is 0.002–0.005 nm. A new method of determination of the ionic radii of elements in unusual valence states is suggested: from the empirical dependence of the electron density at an atom in a given valence state on the atomic radius, a two-parameter equation relating the ionic radii of Period 4–7 elements in two valence states is derived, which allows one to calculate the ionic radius that cannot be determined by crystallography because of the lack of stable compounds in this valence state. Ionic radii are calculated for all Period 4–7 elements in all valence states. They constitute a nearly complete system of ionic radii. There is a linear relationship between the atomic nucleus charge and the inverse ionic radius. It is shown that the square root of the ionization potential is a linear function of the inverse ionic radius. The as yet experimentally unknown ionization potentials of 78 ions of different elements are estimated.     

IONIC THERMOPLASTIC ELASTOMERS: A REVIEW

The incorporation of small amount of ionic groups into hydrocarbon polymers results in unique physical properties and these polymers are called ionomers. They are effectively cross-linked through the association of ionic groups, forming multiplets or clusters. These associations are thermally labile to a greater or lesser extent depending on the composition of the ionic domains. In elastomeric ionomers, the thermolabile nature of the ionic domains permits the adequate flow at the processing temperatures, and hence the term ionic thermoplastic elastomers. Polar plasticizers are incorporated into ion-containing polymers in order to reduce the melt viscosity, resulting from the strong ionic associations, and to improve the processability. The introduction of ionic groups into the block copolymers improves their thermal stability and high temperature performance. The presence of ion-ion interactions in different rubber/plastic blends enhances the mechanical compatibility of the otherwise incompatible blends and thereby results in the formation of ionic thermoplastic elastomers, depending on the rubber to plastic ratios. In the absence of ionic groups the blend components are incompatible, as indicated by poor physical properties of the blends. However, the introduction of ionic groups onto the polymer chains causes a dramatic increase in compatibility between the rubbery and the plastic phases, as indicated by the synergism in physical properties. The present paper reviews the ionic thermoplastic elastomers based on elastomeric ionomers, block copolymer ionomers, and ionomeric polyblends.     

Air and water stable ionic liquids in physical chemistry

Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 degrees C or below. Originating from electrochemistry in AlCl(3) based liquids an enormous progress was made during the recent 10 years to synthesize ionic liquids that can be handled under ambient conditions, and today about 300 ionic liquids are already commercially available. Whereas the main interest is still focussed on organic and technical chemistry, various aspects of physical chemistry in ionic liquids are discussed now in literature. In this review article we give a short overview on physicochemical aspects of ionic liquids, such as physical properties of ionic liquids, nanoparticles, nanotubes, batteries, spectroscopy, thermodynamics and catalysis of/in ionic liquids. The focus is set on air and water stable ionic liquids as they will presumably dominate various fields of chemistry in future.     

离子液体的定量结构-性质/活性研究

本文系统介绍了离子液体定量结构-性质/活性相关(QSPR/QSAR)的研究方法和步骤,综述了QSPR/QSAR在离子液体的熔点、有机物在离子液体中的无限稀释活度系数、离子液体的表面张力、离子液体的电导率、有机物在离子液体中的溶解度、离子液体的黏度以及离子液体的生物毒性和降解性等方面的最新研究进展,总结了该方法的优缺点,并对未来的研究趋势进行了展望。     

Periodicity and map for discovery of new ionic liquids

1 Introduction In undertaking the researches on ionic liquids, we wished to establish periodicity and draw a “map” of ionic liquids for providing definite guidance to dis-cover, design, and choose the proper ionic liquids to meet the specific applicatio…     

New short aliphatic chain ionic liquids: synthesis, physical properties, and catalytic activity in aldol condensations

This paper reports on the synthesis of new short aliphatic chain ionic liquids and the study of the temperature dependence of density, ultrasonic velocities, and ionic conductivity in the range of 278.15-338.15 K. Fourier transform infrared spectra establishes their simple ionic salt structure. Because of their polarity, the ionic liquids are able to dissolve polar solvents and inorganic salts, all of them showing high tolerance in hydroxylic media. The observed temperature trend of the studied properties points out the special packing of these ionic liquids, as well as the strong influence of the steric hindrance among linear aliphatic residues enclosed in anions and cations. One of them showed a very high melting temperature. A collection of slightly basic ionic liquids were used to test their catalytic activity in several aldol condensation reactions of some carbonyl compounds. The best conversions and selectivities were obtained using single ionic liquids, with no synergetic effects being observed when different concentrations of mixed ionic liquids were used as catalysts. In any case, the ionic liquid can also easily be recycled from reaction media, suggesting a promising method of process design for this kind of reaction.     

Influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate: a sum frequency generation analysis

Sum frequency generation spectroscopy (SFG) was used to study the influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The orientation of the cation at the gas-liquid interface was analyzed as a function of ionic liquid concentration in water for concentrations from 0 to 1 mole fraction of the ionic liquid. The cation was found to be oriented with the imidazolium ring nearly parallel to the surface plane with a tilt angle > or = 70 degrees when the ionic liquid was dry. Furthermore, no noticeable change in the orientation was observed when high concentrations of water were mixed with the ionic liquid. The cation butyl chain is projecting into the gas phase with a CH(3) tilt angle of 54 +/- 2 degrees when the ionic liquid is dry and 46 +/- 4 degrees when mixed with water. Water is oriented at the surface only for concentration < or = 0.02 mole fraction of the ionic liquid. At higher ionic liquid concentrations (mole fractions > or = 0.05) the gas-liquid interface resembles that of the pure ionic liquid.     

Synthesis of Multiester-appended and Multicarboxylic-appended Imidazolium Ionic Liquids

Currently ionic liquids (ILs) are attracting considerable interest as eco-friendly solventsfor the replacement of volatile organic solvents in organic synthesis and catalysis1.Low-melting ILs based on imidazolium cations have dominated this area over the …     

Investigation of the effect of ionic strength of Tris-acetate background electrolyte on electrophoretic mobilities of mono-, di-, and trivalent organic anions by capillary electrophoresis

The effect of ionic strength of the background electrolyte (BGE) composed of tris(hydroxymethyl)aminomethane (Tris) and acetic acid on the electrophoretic mobility of mono-, di- and trivalent anions of aliphatic and aromatic carboxylic and sulfonic acids was investigated by capillary zone electrophoresis (CZE). Actual ionic mobilities of the above anions were determined from their CZE separations in Tris-acetate BGEs of pH 8.1 to 8.2 in the 3 to 100 mM ionic strength interval at constant temperature (25 degrees C). It was found that the ionic strength dependence of experimentally determined actual ionic mobilities does not follow the course supposed by the classical Onsager theory. A steeper decrease of actual ionic mobilities with the increasing ionic strength of BGE and a higher estimated limiting mobility of the anions than that found in the literature could be attributed to the specific behavior of the Tris-acetate BGEs. Presumably, not only a single type of interaction of anionic analytes with BGE constituents but rather the combination of effects, such as ion association or complexation equilibria, seems to be responsible for the observed deviation of the concentration dependence of the actual ionic mobilities from the Onsager theory. Additionally, several methods for the determination of limiting ionic mobilities from CZE measured actual ionic mobilities were evaluated. It turned out that the determined limiting ionic mobilities significantly depend on the calculation procedure used.     

Preparation of Ionic Liquid‐based Vilsmier Reagent from Novel Multi‐purpose Dimethyl Formamide‐like Ionic Liquid and Its Application

In continuation of research to explore the applied potential of DMF‐like ionic liquid, the ionic liquid version of N,N‐dimethyliminiumchloride (Vilsmier reagent) has been synthesized from DMF‐like ionic liquid and tested effectively for its capacity to achieve more useful organic transformations. The results show that DMF‐like ionic liquid is world's first task specific ionic liquid which has catalyzed numerous diverse type of reaction and is multipurpose in its application. Thus a new term for this DMF‐like ionic liquid has been coined that is DMF‐like "multipurpose" ionic liquid.     

Matrix-assisted laser desorption/ionization mass spectrometry for the characterization of ionic liquids and the analysis of amino acids, peptides and proteins in ionic liquids

Ionic liquids are interesting solvents for a number of applications in chemistry and biotechnology. We characterized five different ionic liquids by laser desorption/ionization (LDI) and by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) and studied the analysis of amino acids, peptides and proteins dissolved in these solvents. Signals of both anions and cations of the ionic liquids could be observed both in LDI- and in MALDI-MS. In the latter case, adduct formation between anions and cations of the analytes was observed. Amino acids, peptides and proteins could be analyzed in ionic liquids after addition of matrix substances. Sodium and potassium adducts were not observed in any analysis involving ionic liquids. Low molecular mass compounds and peptides could be analyzed best in the presence of water-immiscible ionic liquids, whereas proteins gave the best results in water-miscible ionic liquids. Optimal analysis conditions such as molar matrix-to-analyte and ionic liquid-to-matrix ratios were determined. Homogeneity of samples in the presence of ionic liquids was reduced compared with classical MALDI preparations. Relative quantitation of amino acids was possible using isotope-labeled internal standards. MALDI-MS thus can be used for the analysis of chemical reactions and the screening of enzyme-catalyzed reactions in ionic liquids and for the analysis of the biocatalysts dissolved in these solvents. Theoretical aspects of ion formation in the presence of ionic liquids both in LDI and MALDI analysis are discussed.