After this the work on molten salts took a backseat in the minds of chemists

After this the work on molten salts took a backseat

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were used to carry out his experiments in a water-free environment. After this, the work on molten salts took a backseat in the minds of chemist’s world-wide and it wasn’t until 1982 that work began anew on ionic liquids. Wilkes et al [ 11 ] introduced ionic liquids with an AlCl - 4 anion and 1-alkyl-3-methyl-imidazolium cations. These ionic liquids were however air and water sensitive and it would take another decade until a more robust system was devised. In 1992 Seddon et al., Hussey et al. and Chauvin et al. reported ionic liquid systems based on other anions, mainly BF - 4 , that were less sensitive to moisture than AlCl - 4 . The next significant step was taken in 1998 by Davis et al. [ 6 ] who introduced the ionic liquids that today are sometimes known as designer solvents or third generation ionic liquids. With the introduction of third generation ionic liquids, chemists got access to a new range of solvents for a wide variety of applications. Whilst the term ionic liquid can seems to suggest that we are dealing with systems that should be similar, this is generally far from the norm. The physical and chemical properties of ionic liquids vary and it has thus far proved to be impossible to provide a systematic classification for every ionic liquid that can be synthesized. For instance, most ionic liquids have negligible vapor pressure but there exists ionic liquids that can be distilled [ 12 ]. Whilst there is currently no way to provide a systematic classification system for ionic liquids there are still some definitions that are true for all ionic liquids. For those seeking a more thorough description of ionic liquids there has been several books published on the subject [ 13 , 14 ]. 1
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2 CHAPTER 1. BACKGROUND 1.1.2 Why use ionic liquids Ionic liquids offer a wide array of options and benefits for use as solvents. Depending on what parameters that are important to the situation, different anions and cations can be chosen to give the ionic liquid the sought properties. Currently, one issue is that there are still a lot of unknown combinations and non investigated systems. This is something that through continued investigation is becoming less and less of a concern. Presently one typically chooses an ionic liquid that is close enough to the needs of the process from previously reported anion/cation combinations rather than going through the tedious process of trial and error that is a necessity when the available systems do not fit the requirements. There are a number of reasons to use ionic liquids over more traditional solvents. Whilst there are ionic liquids that do not have all of these properties, the sheer amount of both theoretical (numbering in the millions) and reported (approximately 1500 to date) ionic liquid systems will allow for almost any combination of characteristics to be available in one or more of these systems. If one were to include the advanced ionic liquid systems that are a combination of several simple ionic liquids the possibilities become almost endless. The major advantages of using ionic liquids as solvents include that: they have negligible vapor pressure and do thus not evaporate.
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