INTRODUCTION TO IONIC LIQUIDS

Cole-Hamilton andR. P. Tooze (eds.), Catalyst Separation, Recovery and Recycling, 183-213. 2006 Springer. Printed in the Netherlands. 

In 1992, the ionic liquid methodology received a substantial boost when Wilkes and Zaworotko described the synthesis of non-chloroaluminate, room temperature liquid melts (e. g. low melting tetrafluoroborate melts) which may be regarded as second generation ionic liquids [6]. Nowadays, tetrafluoroborate and (the slightly later published [7]) hexafluorophosphate ionic liquids are still widely used in ionic liquid research. However, their use in many technical applications will be clearly limited by their relatively high sensitivity towards hydrolysis. Of course, the tendency of their anions to hydrolyse is much less pronounced than for the chloroaluminate melts but it still clearly exists. Consequently, the technical application of tetrafluoroborate and hexafluorophosphate ionic liquids will be effectively restricted to those applications where water-free conditions can be realised at acceptable costs. 

The second group of recently developed ionic liquids is often referred to as task specific ionic liquids in the literature [15]. These ionic liquids are designed and optimised for the best performance in high-value-added applications. Functionalised [16], fluorinated [17], deuterated [18] and chiral ionic liquids [19] are expected to play a future role as special solvents for sophisticated synthetic applications, analytical tools (stationary or mobile phases for chromatography, matrixes for MS etc.), sensors and special electrolytes. 

Historically, the know-how to synthesise and handle ionic liquids has been treated in some ways as a holy grail . Indeed, only a small number of specialised industrial and academic research groups were able to prepare and handle the highly hygroscopic 

Nowadays, a number of commercial suppliers [20] offer ionic liquids, some of them in larger quantities, [21] and the quality of commercial ionic liquid samples has clearly improved in recent years. The fact that small amounts of impurities significantly influence the properties of the ionic liquid and especially its usefulness for catalytic reactions [22] makes the quality of an ionic liquid an important consideration [23]. Without any doubt the improved commercial availability of ionic liquids is a key factor for the strongly increasing interest in this new class of liquid materials. 

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For an introduction to ionic liquids see Wasserscheid, P. Welton, T. Ionic liquids in Synthesis, 2003, Wiley VCH, Weinheim. 

M Freemantle, An Introduction to ionic liquids. Royal Society of Chemistry, 2010. 

Freemantle, M., An Introduction to Ionic Liquids (RSC Publications, Cambridge, 2010),... 

Freemantie M (ed, multi-author) (2010) An introduction to ionic liquids. Royal Society of Chemistry, Cambridge, 281 pp... 

P. Wasserscheid and T. Welton, Ionic Liquids in Synthesis, 2nd edn., Wiley-VCH, Weinheim, Germany, 2007 M. Vreemantie, An Introduction to Ionic Liquids, RSC, Cambridge, MA, 2009. 

It is evident firom this brief introduction that ionic liquids may affect reactivity much more than molecular solvents. They are not only mixtures of two species interacting with each other (anion and cation), each able to give specific interactions with the dissolved reagents and/or activated complexes, but the anion-three-dimensional structures able to exercise unusual effects. 

Fig. 13. Glycoside and related structures suitable for facile preparation of cationic derivatives with ultimate conversion to ionic liquids. In each instance a primary hydroxyl is available or readily obtained by simple reduction for introduction of a quaternary ammonium (or phosphonium) site for salt construction.

Section 6.2.1 offers literature data on the electrodeposition of metals and semiconductors from ionic liquids and briefly introduces basic considerations for electrochemical experiments. Section 6.2.2 describes new results from investigations of process at the electrode/ionic liquids interface. This part includes a short introduction to in situ Scanning Tunneling Microscopy. 

INTRODUCTION TO TRANSITION METAL CATALYSIS IN IONIC LIQUIDS... 

Upon dissolving the copolymer/catalyst mixture in ethylbutylamine (EtBuNH) the introduction of CO2 at atmospheric pressure results in formation of an equilibrium mixture of carbamic acid and the quaternary ammonium salt of carbamate. The carbamic acid serves to remove the copolymer from the metal center, at which time it precipitates in the ionic liquid and is isolated by filtration. The metal catalyst... 

Aminocarbonylation provides an efficient method for the synthesis of carboxamides from readily available alkenyl halides. This reaction finds many applications in organic synthesis, especially for the introduction of amides with a variety of A -substituents. For example, steroidal alkenyl iodide 137 was transformed to the corresponding amide derivative 138 in 88% yield through aminocarbonylation (Equation (10)). In this reaction, the palladium catalyst was recovered by using an ionic liquid, l-butyl-3-methylimidazolium salt 139, as reaction media, and reused five times with only a minor loss of activity. ... 

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