Synthesis ionic liquids

From Section 2.1 it has become very clear that the synthesis of an ionic liquid is in general quite simple organic chemistry, while the preparation of an ionic liquid of a certain quality requires some know-how and experience. Since neither distillation nor crystallization can be used to purify ionic liquids after their synthesis (due to their nonvolatility and low melting points), maximum care has to be taken before and during the ionic liquid synthesis to obtain the desired quality. 

Ionic liquid synthesis in a commercial context is in many respects quite different from academic ionic liquid preparation. While, in the commercial scenario, labor-intensive steps add significantly to the price of the product (which, next to quality, is another important criterion for the customer), they can easily be justified in academia to obtain a purer material. In a commercial environment, the desire for absolute quality of the product and the need for a reasonable price have to be reconciled. This is not new, of course. If one looks into the very similar business of phase-transfer catalysts or other ionic modifiers (such as commercially available ammonium salts), one rarely finds absolutely pure materials. Sometimes the active ionic compound is only present in about 85 % purity. However, and this is a crucial point, the product is well specified, the nature of the impurities is known, and the quality of the material is absolutely reproducible from batch to batch. 

A number of different methods to monitor the amount of methylimidazole left in a final ionic liquid are known. NMR spectroscopy is used by most academic groups, but may have a detection limit of about 1 mol%. The photometric analysis described by Holbrey, Seddon, and Wareing has the advantage of being a relatively quick method that can be performed with standard laboratory equipment [13]. This makes it particularly suitable for monitoring of the methylimidazole content during commercial ionic liquid synthesis. The method is based on the formation and colorimetric analysis of the intensely colored complex of l-methylimidazole with cop-per(II) chloride. 

In this context it is important to note that the detection of this land of alkali cation impurity in ionic liquids is not easy with traditional methods for reaction monitoring in ionic liquid synthesis (such as conventional NMR spectroscopy). More specialized procedures are required to quantify the amount of alkali ions in the ionic liquid or the quantitative ratio of organic cation to anion. Quantitative ion chromatography is probably the most powerful tool for this kind of quality analysis. 

For commercial ionic liquid synthesis, quality is a key factor. FFowever, since availability and price are other important criteria for the acceptance of this new solvent concept, the scaling-up of ionic liquid production is a major research interest too. 

Other important aspects to consider during the scaling-up of ionic liquid synthesis are heat management (allcylation reactions are exothermic ) and proper mass transport. For both of these the proper choice of reactor set-up is of crucial importance. 

Cao, S.W., Zhu, Y.J., Cheng, G.F. and Huang, Y.H. (2009) ZnFe204 nanopartides microwave—hydrothermal ionic liquid synthesis and photocatalytic property over phenol. Journal of Hazardous materials, 171 (1—3), 431—435. 

In the following, the reasons for the higher architectural demands are exemplified at two laboratory examples for liquid-liquid Suzuki coupling and imidazol-based ionic liquid synthesis and can only partly be shown in the example of liquid-liquid and gas-liquid processing scale-out. 

An imidazol-based ionic liquid synthesis was carried out under solvent-free conditions, simply bringing the two liquid reactants into contact... 

Fig. 11. Real-time, in-line temperature monitoring for an ionic-liquid synthesis when varying external bath temperature and volume flow...

Lob P, Lowe H, Hessel V, Hubbard SM, Menges G, Balon-Burger M (2006b) Determination of temperature profile within continuous micromixer-tube reactor used for the exothermic addition of dimethyl amine to acrylonitrile and an exothermic ionic liquid synthesis. In Proceedings of AIChE Spring National Meeting, Orlando, 23-27 April, 2006... 

Singh, R. P. Manandhar, S. Shreeve, J. M. Mono- and disubstituted polyfluoroalkylimida-zolium quaternary salts and ionic liquids. Synthesis 2003, 1579-1585. 

Malik, C.K., Vaultier, M., and Ghosh, S. (2007) Copper(I)-catalyzed [2 + 2] photocycloaddition of nonconjugated alkenes in room-temperature ionic liquids. Synthesis, 1247-1250. 

The monomer must be soluble in the ionic liquid at adequate concentrations. Indeed, the solubility of some monomers may be improved using an ionic liquid synthesis of poly(terthiophene) is often hampered by the poor solubility of the monomer, but terthiophene can be dissolved in l-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C2mim][NTf2] or N,N-butylmethylpyrrolidi-nium bis(trifluoromethanesulfonyl)amide, [C4mpyr] [NTf2], at concentrations up to 0.05 M [27]. 

In Chapter 1 we explain the motivation and basic concepts of electrodeposition from ionic liquids. In Chapter 2 an introduction to the principles of ionic liquids synthesis is provided as background for those who may be using these materials for the first time. While most of the ionic liquids discussed in this book are available from commercial sources it is important that the reader is aware of the synthetic methods so that impurity issues are clearly understood. Nonetheless, since a comprehensive summary is beyond the scope of this book the reader is referred for more details to the second edition of Ionic Liquids in Synthesis, edited by Peter Wasserscheid and Tom Welton. Chapter 3 summarizes the physical properties of ionic liquids, and in Chapter 4 selected electrodeposition results are presented. Chapter 4 also highlights some of the troublesome aspects of ionic liquid use. One might expect that with a decomposition potential down to -3 V vs. NHE all available elements could be deposited unfortunately, the situation is not as simple as that and the deposition of tantalum is discussed as an example of the issues. In Chapters 5 to 7 the electrodeposition of alloys is reviewed, together with the deposition of semiconductors and conducting polymers. The deposition of conducting polymers... 

A novel and efficient ionic liquid synthesis of DHPMs has been developed by Bazureau and co-workers [92] in which ionic liquid-phase bound acetoacetate was reacted with (thio)urea and a suitable aldehyde in the presence of HCl affording ionic liquid-phase supported 3,4-dihydropyrimidine-2-(thi)ones 43. The desired 3,4-dihydropyriinidme-2-(thi)one was easily cleaved from the ionic liquid-phase by transesterification under mild conditions in good yield and with high purity. Advantageously, the ionic liquid-phase linked DHPM could be crystallized from the excess of (thio)urea (Scheme 32). 

Zhao D, Fei Z, Ohlin C A, et al. Dual-functionalised ionic liquids Synthesis and characterisation of imidazolium salts with a nitrile-functionalised anion. Chem. Commun. 2004. 2500-2501. 

Kan H C, Tseng M C, Chu Y H. Bicyclic imidazolium-based ionic liquids Synthesis and characterization. Tetrahedron. 2007. 63, 1644-1653. 

Zeng Z, Phillips B S, Xiao J C, et al. Polyfluoroalkyl, polyethylene glycol, 1,4-bismethylenebenzene or l,4-bismethylene-2,3,5,6-tetra-fluorobenzene bridged functionalized dicationic ionic liquids Synthesis and properties as high temperature lubricants. Chemistry of Materials. 2008. 20, 2719-2726. 

Zhao D B, Fei Z F, Geldbach T J, et al. Nitrile-functionalized pyridi-nium ionic liquids Synthesis, characterization, and their application in carbon-carbon coupling reactions. J. Am. Chem. Soc. 2004. 126, 15876-15882. 

Cota 1, Gonzalez-Ohnos R, Iglesias M, et al. New short aliphatic chain ionic liquids Synthesis, physical properties, and catalytic activity in aldol condensations. J. Phys. Chem. B. 2007. Ill, 12468-12477. 

Optically Pure Ionic Liquids - Synthesis and Purification of Ionic Liquids. 286... 

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