Task-Specific Ionic Liquids for Electrochemical Applications

Task-Specific Ionic Liquids for Electrochemical Applications 

2 Ether/Thioether- and Hydroxyl/Thiol-Functionalized ILs 8.2.1 General Physical Properties 

Our recent review has captured some key physical properties of ether- and alcohol-functionalized ILs [22], The inclusion of alkyloxy or alkyloxyalkyl groups in ILs often lowers the melting points (Tm) [23-26], Additionally, the lowering of the 

Department of Chemistry and Forensic Science, Savannah State University, Savannah, GA 31404, USA 

02 mS/cm, a better thermal stability than ILs with alkoxy substituents at the N position, as well as wide electrochemical windows ( 4.2 V). Chai et al. [62] prepared a series of ether-functionahzed trialkylimidazolium ILs (methyl or ethyl group at the C-2 position) carrying [N(Tf 2] anions and reported that 26 ILs have viscosities lower than 100 mPa s (with the lowest value being 54.4 mPa s) at room temperature and these ILs have wide electrochemical windows greater than 

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As one looks back over the last few decades it is possible to see trends emerging in the ionic liquids that are used and the main foci of interest. Early chloroaluminate systems with potential electrochemical applications gave way to ionic liquids with more air stable anions, with interest moving on to chemicals synthesis and catalysis. Then came new systems with specific properties to use as Task Specific Ionic Liquids (see Chapter 3), or for dissolving biomass polymers (Chapter 10), or as engineering fluids of various types. A small number of papers have now appeared on mixtures of ionic liquids. The exciting thing about ionic liquids is that as each development has occurred it has been in addition to the previous activities and not a replacement for these. 

Having said all this we would like to point out very clearly that we consider the constant quest for new, highly functionalized or task-specific ionic liquid structures as a very important part of the development of the whole ionic liquid research area. These may still have many, economically highly attractive applications, even if the total volume of their use is expected to be much smaller. These task-specific ionic liquids are likely to form the key functional materials in devices like sensors or chromatographic columns or the magic ingredient in product formulations, like electrochemical baths or lubricants. 

The last two decades have seen an explosion of interest in ionic liquids [1]. Their use as solvents has been the subject of widespread academic study [2] and they have been applied in a number of commercial processes [3]. Much of the interest in ionic liquids has centered on their possible use as green solvents [4]. However, this has been the subject of much controversy [5], and the concept of a green solvent itself is now somewhat dated. There have been many reviews of ionic liquids. Some of these have focused on particular applications, for example, analysis [6], biocatalysis [7], catalysis [8], electrochemical devices [9], or engineering fluids [10]. Others have concentrated on particular subgroups of ionic liquids, for example, task-specific ionic liquids [11]. This chapter summarizes what is known about the physicochemical properties that are of particular interest for supported ionic hquid phases (SILPs). 

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