Development of Ionic Liquids as Green Reaction Media and Catalysts

A brief review of the work carried out at Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences for development of ionic liquid as green reaction media and catalysts is presented. This includes the processes of ionic liquid to be used as catalyst, reaction media, development of functional ionic liquid and methods for synthesis of immobilized ionic liquid. In the end, some prospects for development of ionic liquid are also addressed.     

离子液体中脂肪酶催化酯类合成的新进展

作为21世纪最具发展潜力的绿色溶剂,离子液体用于酶促合成的反应介质具有得天独厚的优势.与传统的有机溶剂相比,离子液体能够提高脂肪酶的稳定性和选择性,减少有机合成中的副反应和有毒气体的产生,后处理简单,可重复利用.参考10年来的文献,从脂肪酶催化酯类合成的常用离子液体种类、过程因素及场/反应器强化等方面进行了综述,同时展望了离子液体在未来酯类酶促合成领域的发展趋势.     

离子液中溶剂化电子的结构及其演化动力学

本文综述了离子型液体介质中过剩电子的结构、存在状态及其时间演化动力学特征。基于从头算分子动力学模拟及计算结果,重点阐述了咪唑型、吡啶型、碱金属离子型熔盐氯化物离子液中与过剩电子溶剂化密切相关的溶剂化能量学、结构特征、可能的存在状态以及态-态转化稳态动力学机制,分析了此类离子型介质中电子高效传导的内在本质及离子液组成离子的重要作用。阳离子的最低未占轨道组成的导带结构是离子液中过剩电子的溶剂化态及其稳定性的决定因素,任何能影响或改变其导带结构的因素均能显著影响过剩电子溶剂化。但快速的态-态转化及电子迁移并不明显取决于其组成离子扩散动力学,而是敏感地受离子液涨落所控制。这种基于溶剂化电子的迁移模式构成了此类离子型介质甚至其它液态介质中电子转移的新途径。     

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.     

Comparing π-complexation capabilities of ionic liquids containing silver(I) and copper(I) ions by headspace single drop microextraction in combination with high-performance liquid chromatography

Selective π-complexation capabilities of silver(I) and copper(I) ions can be effectively facilitated in ionic liquids. To understand the effects of environmental factors that influence the π-complexation of these metal ions with analytes, techniques that employ small volumes of ionic liquid that can be readily analyzed are desired. In this study, headspace single drop microextraction coupled with HPLC is used to investigate a diverse set of environmental factors on the metal ion-mediated complexation with aromatic compounds in ionic liquid media. Silver(I) and copper(I) bis[(trifluoromethyl)sulfonyl]imide salts were both studied by dissolving them in the 1-decyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ionic liquid and employing the mixture as extraction media for aromatic compounds. Water and acetonitrile within the sample solution were observed to interfere with the complexation of silver(I) ions and aromatic compounds, while ethylene glycol and triethylene glycol did not. The temperature and extraction times were optimized to fully facilitate the π-complexation capabilities of metal ions in ionic liquid media. Partition coefficients between the sample headspace and metal ion were determined using a three-phase equilibria model. Although no discernable difference in analyte partitioning between the headspace and ionic liquid solvent was observed, analyte partition coefficients to silver(I) ion tended to be greater compared to copper(I) ion.     

Efficient carbonylation reactions in phosphonium salt ionic liquids: anionic effects

Application of phosphonium salt ionic liquids in the carbonylation of aryl and vinyl halides is presented. Anionic effects were uncovered with the bromide ionic liquid emerging as the superior media. Acid bromide intermediates were detected in control experiments providing an extended view on the overall catalytic cycle involved. Solvent-free product isolation and recycling of the ionic liquid containing active Pd-catalyst are also demonstrated.     

Palladium-catalyzed thiocarbonylation of iodoarenes with thiols in phosphonium salt ionic liquids

Trihexyl(tetradecyl)phosphonium hexafluorophosphate, a phosphonium salt ionic liquid (PSIL) is a particularly effective general reaction media for the Pd-catalyzed carbonylation reaction of iodoarenes and thiols to form thioesters. Recycling of the ionic liquid containing active Pd-catalyst was also demonstrated.     

Exploration of ionic liquids as soluble supports for organic synthesis. Demonstration with a Suzuki coupling reaction

The efficiency of ionic liquid supported synthesis was demonstrated by the Suzuki reaction of ionic liquid supported iodobenzoate compounds with arylboronic acids in aqueous media to give, after cleavage with ammonia/methanol, biaryl products in good yields and high purities, without the need for chromatographic purification. [reaction: see text]     

Electrochemical oxidation of primary amine in ionic liquid media: Formation of organic layer attached to electrode surface

Electrochemical oxidation of primary amine in ionic liquid media has been investigated. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Two primary amine compounds are used for this study; 4-nitrobenzylamine and 2-aminoethylferrocenylmethylether. The oxidation of the amino compounds in ionic liquid conduces to the modification of the electrode surface. The modified electrodes were characterized by cyclic voltammetry and XPS analysis. Both techniques support the presence of an organic layer strongly attached onto the electrode surface. The surface concentration of the attached group obtained in this media was found to be around 1 to 3 × 10^?10 mol cm^?2. The use of ionic liquid as media for the grafting leads to decrease of the surface concentration of the grafted layer; and the formation of less dense layer compared with classical solvent such as acetonitrile.     

Insight into the interactions that control the phase behaviour of new aqueous biphasic systems composed of polyethylene glycol polymers and ionic liquids

New polyethylene glycol (PEG)/ionic liquid aqueous biphasic systems (ABS) are presented. Distinct pairs of PEG polymers and ionic liquids can induce phase separation in aqueous media when dissolved at appropriate concentrations. Phase diagrams have been determined for a large array of systems at 298, 308 and 323 K. A comparison of the binodal curves allowed the analysis of the tunable structural features of the ionic liquid (i.e., anionic nature, cationic core, cationic alkyl side chain length and functionalisation, and number of alkyl substituents in the cation) and the influence of the molecular weight of the PEG polymer on the ability of these solutes to induce an ABS. It was observed that contrary to typical ABS based on ionic liquids and inorganic salts, in which the phase behaviour is dominated by the formation of the hydration complexes of the ions, the interactions between the PEG polymers and ionic liquids control the phase demixing in the polymer-type ABS studied herein. It is shown that both the ionic liquids and PEG polymers can act as the salting-out species; that is, it is an occurrence that is dependent on the structural features of the ionic liquid. For the first time, PEG/ionic liquid ABS are reported and insight into the major interactions that govern the polymer/ionic liquid phase behaviour in aqueous media are provided. The use of two different nonvolatile and tunable species (i.e., ionic liquids and PEG polymers) to form ABS allows the polarities of the phases to be tailored. Hence, the development of environmentally friendly separation processes that make use of these novel systems is envisaged.     

Ionic liquid mediated recyclable sulphonimide based organocatalysis for aldol reaction

Sulphonimide based organocatalyst was used to catalyze the aldol reaction in ionic liquid media. On the basis of yield and selectivity the ionic liquid mediated system was found superior in comparison with organic solvents. The added advantages of this ionic liquid mediated organocatalysis are easy recovery of product and the recyclability of the organocatalyst.      

Modification of carbon electrode in ionic liquid through the reduction of phenyl diazonium salt. Electrochemical evidence in ionic liquid

Electrochemical reduction of the 4-nitrophenyl diazonium salt in ionic liquid media has been investigated at carbon electrode. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The cyclic voltammetry study demonstrated the possibility of the electrochemical grafting of the nitrophenyl groups onto carbon electrode after the reduction of its corresponding diazonium in ionic liquid. The electrochemical characterization of the modified electrode achieved on ionic liquid displays the presence of the nitrophenyl group at the carbon surface. Moreover, the surface concentration of the attached group obtained in this media was found to be around 1.7 × 10⁻¹⁰ mol cm⁻², this value may suggest the possibility of the formation of monolayer. Furthermore, the characterization of the modified electrode in [EMIM][TFSI] showed the conversion of some NO₂-phenyl groups to NHOH-phenyl. This observation could indicate the presence of surface interaction between the reduced NO₂-phenyl and the ionic liquid cation, thanks to the presence of acidic proton in the ionic liquid cation.     

Practical considerations associated with voltammetric studies in room temperature ionic liquids

Recent developments associated with voltammetric studies in ionic liquid media have been critically reviewed. Initially, advantageous electrochemical properties of ionic liquids are summarised, as are limitations encountered by the presence of impurities and problems related to purification and recovery of ionic liquids. Subsequently, the use of IUPAC recommended ferrocene oxidation and cobalticenium reduction processes as potential reference scales in ionic liquids and the application of voltammetry of adhered solid and microchemical approaches to the measurement of formal potentials and kinetics of coupled first order chemical reactions are discussed. Finally, the possible use of volatile ionic liquids is considered as an alternative to use of the non-volatile ionic liquids media, presently emphasized in most studies.     

Amberlyst‐15‐Catalyzed Novel Synthesis of Quinoline Derivatives in Ionic Liquid

In recent years, ionic liquids have attracted much attention as useful synthetic solvents. Compared with classical molecular solvents, the ionic liquids are environmentally benign reaction media. A variety of quinoline derivatives have been synthesized under ionic liquid conditions using Amberlyst‐15 as catalyst.     

Synthesis of gold nanoparticles modified with ionic liquid based on the imidazolium cation

The synthesis and processing of nanoparticles consisting of metallic nanocrystal cores and organic monolayer shells promise interesting technological applications. Here, we report the synthesis of gold nanoparticles modified with ionic liquids based on the imidazolium cation. Aggregation-induced color changes of the gold nanoparticles in an aqueous solution were used as an optical sensor for anions via anion exchange of ionic liquid moiety. We also demonstrated the phase transfer of the gold nanoparticles from aqueous media to ionic liquid.     

Direct catalytic asymmetric cross-aldol reactions in ionic liquid media

Enantioselective proline-catalyzed direct asymmetric cross-aldol reactions with aldehydes were performed in ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate media, which simplified product isolation and catalyst recycling, affording 3-hydroxy aldehydes in high yield with excellent stereoselectivity. In addition, the enhanced reactivity of the asymmetric cross-aldol reactions in ionic liquid allowed the catalyst loading to be lowered significantly.     

离子液体在CO_2捕集中的应用进展

离子液体具有蒸汽压极低、热稳定性好、热容低和可以根据目标需求进行设计等特性,能克服传统CO2捕集工艺的诸多不足,因而成为目前CO2捕集溶剂的研究热点。本文主要综述了普通离子液体、功能化离子液体、支撑型离子液体膜、聚合型离子液体和离子液体复配溶液在CO2捕集方面的应用研究进展,评述了各种方法的优势和缺点,并在此基础上提出...     

Intermolecular hydroamination and hydroarylation reactions of alkenes in ionic liquids

Intermolecular hydroamination or hydroarylation reactions of norbornene and cyclohexadiene performed with catalytic amounts of Brönsted or Lewis acid in ionic liquids were found to provide higher selectivity and yields than those performed in classical organic solvents. The ionic liquid increases the acidity of the media and stabilizes ionic intermediates through the formation of supramolecular aggregates.     

Activation of C-F bonds in ionic liquids catalyzed by nickel complex compounds

A nickel complex-catalyzed hydrodefluorination of acet(pentafluoroanilide) with zinc in ionic liquids resulted in the corresponding 2,3,4,5-tetrafluoro, 3,4,5-trifluoro, and 3,4-difluoro derivatives. The influence of the ionic liquid nature and the reaction conditions on its selectivity were studied, a possibility of the multiple reuse of the ionic liquids as the reaction media was demonstrated.     

The complex story of a simple Brønsted acid: unusual speciation of HBr in an ionic liquid medium

Crystalline solids, co-existing in equilibrium with the 3-methyl-1H-imidazolium bromohydrogenates(I) ionic liquid, have been characterised by X-ray diffraction analysis. The Br?nsted acidic, homo-conjugate [H(2)Br(3)](-) anions presented are discussed in terms of their structure and reactivity, in efforts to advance the understanding of Br?nsted acidity in ionic liquid media.