The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

1‐n‐Butyl‐2,3‐dimethylimidazolium (BMMI) ionic liquids (ILs) associated with different anions undergo H/D exchange preferentially at 2‐Me group of the imidazolium in deuterated solvents. This process is mainly related to the existence of ion pairs rather than the anion basicity. The H/D exchange occurs in solvents (CDCl₃ and MeCN for instance) in which intimate contact ion pairs are present and the anion possesses a labile H in its structure, such as hydrogen carbonate and prolinate. In D₂O, separated ion pairs are formed and the H/D exchange does not occur. A plausible catalytic cycle is that the IL behaves as a neutral base in the course of all H/D exchange processes. NMR experiments, density functional calculations, and molecular dynamics simulations corroborate these hypotheses.     

An Internal Fluorescent Probe Based on Anthracene to Evaluate Cation–Anion Interactions in Imidazolium Salts

A series of fluorescent imidazolium‐based salts containing the cation [AnCH₂MeIm]⁺ (in which An=anthracene and Im=the imidazolium cation) with Cl^?, BF₄^?, PF₆^?, SO₃CF₃^?, [N(CN)₂]^?, [N(SO₂CF₃)₂]^?, or PhBF₃^? anions have been prepared and characterized. X‐ray diffraction analysis of four of the salts reveals a number of C? H???X‐type (X=O, N, F) hydrogen bonds between the hydrogen atoms from the imidazolium ring and in some cases from the anthracene ring with the electronegative atoms of the anions. Additionally, C? H???π interactions can be found in all the salts analyzed by X‐ray diffraction, whereas π–π stacking is observed only in the salt containing the phenyltrifluoroborate anion. Fluorescence emission analysis in acetonitrile shows that the fluorescence of these salts varies significantly according to the nature of the anion, and correlates to the extent of ion pairing present in solution. Photodimerization of these salts was observed, and in one case a dimer has been isolated and characterized by X‐ray crystallography.     

From Salts to Ionic Liquids by Systematic Structural Modifications: A Rational Approach Towards the Efficient Modular Synthesis of Enantiopure Imidazolium Salts

This paper reports a simple and robust modular synthetic strategy that leads to a large variety of configurationally and structurally diverse imidazole‐based chiral ionic liquids (CILs) by lipase‐catalyzed resolution. The intimate microscopic interactions of the supramolecular ionic network of these imidazolium chiral salts at the molecular level are investigated both spectroscopically (NMR, FT‐IR‐ATR) and theoretically, and a topological analysis of the experimental electron densities obtained by X‐ray dif fr action of single crystals is performed. Our results support the key role played by the relative configuration of the ‐OR group on the hydrogen‐bonding pattern and its strong influence on the final physical properties of the imidazolium salt. We also obtained a reasonable correlation between the observed melting point and the non‐covalent interactions. The spectroscopic data and the topological analysis reflect the key role played by hydrogen bonds between the OH and imidazolium C2H groups in both cation–anion and cation–cation interactions, with the presence of an OH group leading to an additional inter‐cation interaction. This interaction significantly affects the properties of stereoisomeric salts. Even more interestingly, we also studied the effect of the chirality by comparing enantiopure CILs with their racemic mixtures and found that, with the exception of trans‐Cy6‐OH‐Im‐Bn‐Br, the melting points of the racemic mixtures are higher than those of the corresponding enantiomerically pure forms. For stereoisomeric examples, we have successfully explained the differences in melting temperatures in light of the corresponding structural data. Chirality should therefore be taken into account as a highly attractive design vector in the preparation of ILs with specifically desired properties.     

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

Chiral imidazolium l-prolinate salts, providing a complex network of supramolecular interaction in a chiral environment, have been studied as synzymatic catalytic systems. They are demonstrated to be green and efficient chiral organocatalysts for direct asymmetric aldol reactions at room temperature. The corresponding aldol products were obtained with moderate to good enantioselectivities. The influence of the presence of chirality in both the imidazolium cation and the prolinate anion on the transfer of chirality from the organocatalyst to the aldol product has been studied. Moreover, interesting match/mismatch situations have been observed regarding configuration of chirality of the two components through the analysis of results for organocatalysts derived from both enantiomers of prolinate (R/S) and the trans/cis isomers for the chiral fragment of the cation. This is associated with differences in the corresponding reaction rates but also to the different tendencies for the formation of aggregates, as evidenced by nonlinear effects studies (NLE). Excellent activities, selectivities, and enantioselectivities could be achieved by an appropriate selection of the structural elements at the cation and anion.     

利用超额拉曼光谱研究硝酸镁水溶液中的离子对

利用超额拉曼光谱研究了室温下硝酸镁(Mg(NO₃)₂)溶液的离子缔合情况. 测量了该溶液羟基(－OH)伸 缩振动谱段和NO₃^-全对称伸缩振动谱段的拉曼光谱, 利用超额拉曼光谱及光谱拟合分析了这些光谱数据. － OH伸缩振动谱段的超额拉曼光谱显示, 低浓度(<2.3 mol·kg^-1)下阴离子第一水合层的水分子含量随溶液浓度 的升高呈线性关系增加, 在较高浓度时(>2.3 mol·kg^-1), 该含量变化偏离了线性关系, 这是因为Mg(NO₃)₂溶液 在高浓度时存在直接接触离子对导致的. 同样的转折点浓度也在对NO₃^- 全对称伸缩振动谱段的分析中被观测 到. 除了直接接触离子对, 还观测到三种溶剂分隔型离子对. 对该谱段下所有浓度的拉曼光谱和超额光谱进行 同时拟合, 给出了不同浓度下各种离子对的相对含量, 结果显示在0.23-4.86 mol·kg^-1浓度范围内都有溶剂分 隔型离子对和直接接触型离子对. 当Mg(NO₃)₂浓度低于2.3 mol·kg^-1时, 所有离子对的相对含量随浓度增加呈 现直线上升, 在高于这个浓度后直接接触离子对的相对含量急剧增加, 一种溶剂分隔型离子对的相对含量增加 变缓, 另一种溶剂分隔型离子对的相对含量逐渐减少, 还有一种溶剂分隔型离子对相对含量的增加趋势保持不 变, 在Mg(NO₃)₂浓度大于3.5 mol·kg^-1后, 其相对含量不再发生明显变化.     

Stable and Oriented Liquid Crystal Droplets Stabilized by Imidazolium Ionic Liquids

Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In this work, we explore, for the first time, the potential of surface-active ionic liquids of the imidazolium family as surfactants to generate in high yield, stable and oriented liquid crystal droplets. Our results show that [C₁₂MIM][Cl], in particular, yields stable, uniform and monodisperse droplets (diameter 74 ± 6 µm; PDI = 8%) with the liquid crystal in a radial configuration, even when compared with the standard SDS surfactant. These findings reveal an additional application for ionic liquids in the field of soft matter.     

Formation of “Quasi” Contact or Solvent‐separated Ion Pairs in the Local Environment of Probe Molecules Dissolved in Ionic Liquids

The change from “quasi” contact to “quasi” solvent‐separated ion‐pair configuration in the local environment of a probe molecule in ionic liquids depends on the varying interaction strength of the chosen anions. The ion speciation in these Coulomb fluids could be shown by combining infrared spectroscopy, density functional theory calculations, and natural bond orbital analysis using a low‐self‐clustering probe molecule.     

The Peculiar Nature of Molecular Interactions between an Imidazolium Ionic Liquid and Acetone

We present novel insights into the molecular interactions between polar solvents and imidazolium ionic liquids using the example of 1‐ethyl‐3‐methylimidazolium ethyl sulfate and acetone. Recently published volumetric property data of this particular system have revealed peculiarities which could not be fully explained by steric effects. In order to shed light on the behavior at a molecular level, we apply IR spectroscopy and analyze solvent‐induced line shifts as well as the excess IR spectra. From the spectroscopic results a conclusive picture of the site‐specific molecular interactions is developed and our explanation is in concert with the volumetric effects. The data suggest the initial formation of trimers in which acetone interacts with existing ion pairs through interactions of the acetone oxygen atom with the imidazolium ring rather than forming directed hydrogen bonds at the CH moieties. With further addition of acetone, tetramers are formed which significantly weaken the interionic interactions and eventually initiate ion pair dissociation. Once the ions are released, the anion is rapidly saturated with acetone while the cation solvation proceeds more slowly with acetone addition.     

离子液体中卤素离子杂质的离子色谱-直接电导检测法分析

研究了离子色谱-直接电导检测法分离测定离子液体中的卤素离子(F~-、Cl~-、Br~-)杂质.采用Shim-pack IC-A3阴离子交换色谱柱,考察了淋洗液种类及浓度、流速和色谱柱温度对分离测定的影响.最佳色谱条件为:以1.25 mmol/L邻苯二甲酸氢钾为淋洗液,流速1.5 mL/min,色谱柱温45 ℃.在此条件下可以基线分离卤素离子,且NO~-_3、BF~-_4、SO~(2-)_4不干扰测定.该法测定卤素离子的检出限(S/N=3)为0.02 ～0.11 mg/L,峰面积的相对标准偏差(n=5)不大于0.7%,F~-、Cl~- 和Br~- 的标准曲线的线性范围分别为0.1 ～50、0.1 ～50、0.5 ～100 mg/L.将方法用于烷基咪唑四氟硼酸盐离子液体中卤素离子杂质的测定,加标回收率为98% ～102%.     

1‐Carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium chloride 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions

The title compound, C₆H₉N₂O₂⁺·Cl⁻·C₆H₈N₂O₂·H₂O, contains one 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate inner salt molecule, one 1‐carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O—H...Cl hydrogen bonds, forming an infinite one‐dimensional chain. The chloride anions are also linked by two weak C—H...Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O—H...O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D‐type absorption in the region below 1300 cm⁻¹ and is different to that of 1‐carboxymethyl‐3‐methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96 , 436–443].     

Synthesis of novel spiro imidazolium salts as chiral ionic liquids

A library of 13 novel chiral spiro imidazolium salts has been synthesized. The effects of N-substituents and counteranions on the melting point of spiro bis(imidazolium) salts are studied in efforts toward the development of room temperature chiral ionic liquids.     

离子对色谱法同时分离测定吡啶及咪唑离子液体阳离子

建立了用紫外检测的反相离子对色谱梯度淋洗同时分离测定4种吡啶离子液体阳离子和5种咪唑离子液体阳离子的方法。实验采用ZORBAX Eclipse XDB-C18反相色谱柱,以离子对试剂水溶液(用柠檬酸调节pH值)+乙腈为流动相,考察了离子对试剂种类和浓度、乙腈浓度和色谱柱温度对保留的影响,探讨了相关保留规律,确定最佳色谱条件为:流速1.0 mL/min、柱温30℃,以1.0 mmol/L庚烷磺酸钠水溶液(pH 4.0)-乙腈为淋洗液进行梯度洗脱。在此条件下,4种吡啶阳离子和5种咪唑阳离子在15 min内达到基线分离。检出限(S/N=3)为0.31～0.54 mg/L,峰面积的相对标准偏差为0.10%～0.75%。将该方法用于实验室合成的离子液体样品分析,加标回收率为94%～98%。该方法准确、可靠,具有较好的实用性。     

Effect of two Kinds of Imidazolium Ionic Liquids on the Microemulsion Polymerization of Methyl methylacrylate

Summary: In this paper, the microemulsion polymerization of methyl methylacrylate (MMA) was carried out with single and gemini ionic liquids as emulsifier including 1-N-tetradecyl-3-methylimidazolium bromide (C₁₄MIM · Br) and 1, 4-Bis (3-tetradecylimidazolium-1-yl) butane bromide (C₁₄MIM-4-C₁₄MIM · 2Br) respectively, and they were all have typical microemulsion polymerization characters of MMA, but the process of polymerization directly depends on the structure of the imidazolium ionic liquids. The structure and concentration of ionic liquids have effects on the resulted latex particle sizes of PMMA, and much smaller size latexes of PMMA could be gotten with C₁₄MIM · Br as emulsifier than C₁₄MIM-4-C₁₄MIM · 2Br in polymerization. On the other hand, the structure of emulsifier has the effects on the molecular weight (MW) and molecular weight distribution (MWD) of PMMA, so the resulting PMMA prepared from microemulsion polymerization with C₁₄MIM · Br as emulsifier has higher MW but narrower MWD than that of PMMA with the same dosage of C₁₄MIM-4-C₁₄MIM · 2Br as emulsifier.     

吡啶离子液体阳离子的离子色谱法分析

建立了离子色谱-直接电导检测法分离测定3种吡啶离子液体阳离子(N-乙基吡啶、N-丁基吡啶和N-己基吡啶阳离子)的方法.采用磺酸型阳离子交换色谱柱,以乙二胺-柠檬酸-乙腈为淋洗液,考察了淋洗液种类和浓度以及色谱柱温度对离子液体阳离子保留的影响.实验发现,吡啶阳离子的保留过程是放热过程,其同系物的保留符合碳数规律.优化的色...     

Tailored Palladate Tunable Aryl Alkyl Ionic Liquids (TAAILs)

We present a new class of tunable aryl alkyl ionic liquids (TAAILs) containing different palladate counter ions. Solid-state structures for representative compounds have been obtained. Their properties are presented in comparison to those of newly synthesized and reported palladate ionic liquids with conventional counter ions. It was found that the aryl substitution pattern and the type of anion have a profound influence on the melting point. The speciation of the different anions in solution has been rationalized by DFT calculations.