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“Ionic liquids will never find application in industry”, “I don’t understand this fad for ionic liquids” and “there is no widespread interest in these systems” are just three of quotes from the reports of referees for research proposals that I have received over the years. I wonder what these people think today. There are currently at least nine large-scale industrial uses of ionic liquids, including, we now rec- nise, the production of ?-Caprolactam (a monomer for the production of nylon-6) [1]. There has been a steady increase in the interest in ionic liquids for well over a decade and last year the number of papers and patents including ionic liquids was counted in the thousands. This remarkable achievement has been built on the hard work and enthusiasm, first of a small band of devotees, but now of huge numbers of scientists all over the world who do not see themselves as specialists in ionic liquids. The ionic liquids field continues to develop at an incredible rate. No sooner do I think that I am on top of the literature than it turns out that a whole new area of work has emerged without me noticing. Things that were once supposedly impos- 1 sible in ionic liquids, such as measuring the H NMR of solutes, are now widely applicable (see Chapter 8). Hence, collected volumes such as this are very w- come.

Inhaltsverzeichnis

Frontmatter

Synthesis, Purification and Characterization of Ionic Liquids

The synthesis, purification and characterization of ionic liquids is reviewed. The major synthetic routes to low melting ionic salts are described in detail. The intrinsic properties of ionic liquids make purification difficult and therefore a special emphasis is placed on currently employed purification methodologies. Synthetic methods which are designed to avoid specific impurities are also discussed. For the same reasons highlighted above characterization of ionic liquids presents unique challenges; the available methods and some of the issues of their use are also reviewed.

Bronya Clare, Amal Sirwardana, Douglas R. MacFarlane

Ionic Liquid Structure-Induced Effects on Organic Reactions

Understanding the ways in which the constituents of ionic liquids, i.e. the type of cation, its substitution, and the type of anion chosen, interact with reactants is prerequisite to deliberately designing an ionic liquid solvent with optimum performance. Several approaches, including physico-chemical and spectroscopic measurements and computational studies of binary ionic liquid-substrate mixtures have been presented that investigate the strength of interactions.

The qualitative order of the basicity (hydrogen bond acceptor potential) of anions as most prominent force is already reasonably well understood, and reliably determined using, e.g. selective solvatochromic dyes. In certain reactions, the relative order of basicity correlates well with the reactivity of substrates. However, the determination of a relative order for the cations is still in its infancy. Owing to the fact that potential cation-derived interactions may not solely be due to hydrogen bond interactions, but also to ion pair interactions (electron pair donor/acceptor properties), the relative magnitudes of interactions between the anion and cation vary considerably – even in the absence of solutes – depending on the experimental method. In addition, it appears that the basicity of the anion superimposes in many instances on the effects exhibited by the cation and/or the cation’s substituent. Hence, understanding the effect of the cation on the activation of substrates is still a challenge.

This chapter aims at summarising the trends observed for binary model systems in experimental and computational investigations, and drawing conclusions about ionic liquid structure-induced effects relevant to organic reactions, in particular nucleophilic substitution reactions.

Annegret Stark

Task Specific Ionic Liquids and Task Specific Onium Salts

Task specific ionic liquids (TSILs), or more generally task specific onium salts (TSOSs), can be defined as an association of a cation and anion, one at least being organic, to which has covalently been attached through a linker a function that confers the assembly a specific task. After presentation of the general concept of TSILs and TSOSs, the different methods of preparation of these compounds are developed. Regarding their applications in chemistry, TSILs and TSOSs can be used as soluble supports for reagents and catalysts in multiphasic reactions, enabling high activity and easy recovery of the supported agent. However, additionally, they can be used as soluble supports for organic synthesis in a similar manner to resins and offer several advantages over traditional methods.

Mathieu Pucheault, Michel Vaultier

Heavy Elements in Ionic Liquids

Heavy elements have in the recent past been studied extensively in the context of ionic liquids (ILs). This is because ILs have initially been thought of as “solve-it-all” problem solvers, from catalysis, to extraction, and inorganic and electrochemistry. In due course, it has been shown that ILs are indeed very versatile solvents and reaction media. As a consequence, many elements have been dissolved in ILs and their properties have been studied in IL solution. The current chapter focuses on the use of ILs for inorganic chemistry, in particular on what heavy elements have been studied in ILs, their properties and applications.

Andreas Taubert

Thermodynamics and Micro Heterogeneity of Ionic Liquids

The high degree of organisation in the fluid phase of room-temperature ionic liquids has major consequences on their macroscopic properties, namely on their behaviour as solvents. This nanoscale self-organisation is the result of an interplay between two types of interaction in the liquid phase – Coulomb and van der Waals – that eventually leads to the formation of medium-range structures and the recognition of some ionic liquids as composed of a high-charge density, cohesive network permeated by low-charge density regions.

In this chapter, the structure of the ionic liquids will be explored and some of their consequences to the properties of ionic liquids analyzed.

Margarida F. Costa Gomes, J. N. Canongia Lopes, A. A. H. Padua

Thermophysical Properties of Ionic Liquids

Low melting point salts which are often classified as ionic liquids have received significant attention from research groups and industry for a range of novel applications. Many of these require a thorough knowledge of the thermophysical properties of the pure fluids and their mixtures. Despite this need, the necessary experimental data for many properties is scarce and often inconsistent between the various sources. By using accurate data, predictive physical models can be developed which are highly useful and some would consider essential if ionic liquids are to realize their full potential. This is particularly true if one can use them to design new ionic liquids which maximize key desired attributes. Therefore there is a growing interest in the ability to predict the physical properties and behavior of ionic liquids from simple structural information either by using group contribution methods or directly from computer simulations where recent advances in computational techniques are providing insight into physical processes within these fluids. Given the importance of these properties this review will discuss the recent advances in our understanding, prediction and correlation of selected ionic liquid physical properties.

David Rooney, Johan Jacquemin, Ramesh Gardas

Ionic Liquids from Theoretical Investigations

Theoretical investigations of ionic liquids are reviewed. Three main cate-gories are discussed, i.e., static quantum chemical calculations (electronic structure methods), traditional molecular dynamics simulations and first-principles molecular dynamics simulations. Simple models are reviewed in brief.

Barbara Kirchner

NMR Spectroscopy in Ionic Liquds

Today, NMR spectroscopy is

the

most important analytical tool for synthetically working chemists. This review describes the development of NMR spectroscopic methods for use in ionic liquid media and the state-of-the art in terms of routine analytics as well as modern advanced techniques.

Ralf Giernoth

Optical Spectroscopy and Ionic Liquids

Ionic liquids have shown to be excellent solvents for optical investigation of solutes. Transition metal complexes as well as

f

-element compounds have been studied in ionic liquids. Not only are neat and clean ionic liquids transparent in the NIR and visible region, but the absence of anions with low frequency oscillators such as C–H, N–H and O–H have been found to be favourable when it comes to photoluminescence and future applications can be envisioned. Of fundamental interest is the study of the absorption spectra of organic dyes dissolved in an ionic liquid as the many physicochemical parameters such as the dipolarity and polarizability of the ionic liquid and its hydrogen bond ability can be determined.

Anja-Verena Mudring

Ionic Liquids in Biomass Processing

Ionic liquids have been studied for their special solvent properties in a wide range of processes, including reactions involving carbohydrates such as cellulose and glucose. Biomass is a widely available and renewable resource that is likely to become an economically viable source of starting materials for chemical and fuel production, especially with the price of petroleum set to increase as supplies are diminished. Biopolymers such as cellulose, hemicellulose and lignin may be converted to useful products, either by direct functionalisation of the polymers or depolymerisation to monomers, followed by microbial or chemical conversion to useful chemicals. Major barriers to the effective conversion of biomass currently include the high crystallinity of cellulose, high reactivity of carbohydrates and lignin, insolubility of cellulose in conventional solvents, as well as heterogeneity in the native lignocellulosic materials and in lignin itself. This combination of factors often results in highly heterogeneous depolymerisation products, which make efficient separation difficult. Thus the extraction, depolymerisation and conversion of biopolymers will require novel reaction systems in order to be both economically attractive and environmentally benign. The solubility of biopolymers in ionic liquids is a major advantage of their use, allowing homogeneous reaction conditions, and this has stimulated a growing research effort in this field. This review examines current research involving the use of ionic liquids in biomass reactions, with perspectives on how it relates to green chemistry, economic viability, and conventional biomass processes.

Suzie Su Yin Tan, Douglas R. MacFarlane

Backmatter

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