The anions and cations can be varied to get the required end product. Ionic liquids have large anions and cations of low symmetry to reduce the lattice energy and reduce the melting point of the salts. Anions contribute towards the functions and chemistry of ILs and cations contribute towards the variable physical properties and stability of ILs (Bӧhme 2006). Ionic salts can be simple salts i.e. made up of one type of anion and cation or binary ionic liquids which are a mixture of two salts with varying melting points depending on their composition.
Ionic liquids are used to substitute traditional solvents like volatile organic compounds (VOC’s) for their variable properties, low energy inputs and reusability. They are also used to extract various compounds such as metal ions, biomolecules and organosulfurs by using two phase extraction. The most commonly studied systems contain ammonium, phosphonium, sulfonium, pyridinium, imidazolium and pyrrolidinium cations. Common anions include hexafluorophosphate [PF]6-, tetrafluoroborate [BF]4-, bis(trifyl)imide [NTf]2 and chloride, Cl-.
Ionic liquids help in minimizing and eliminating waste, improves chemical syntheses and extractions or separations (Holbrey, Turner & Rogers 2003). The reaction solvents are reusable and do not diminish in content which is a major advantage over traditional solvents that are sometimes volatile like the VOC’s.
However, the most important feature of these ionic liquids that has led to the great amount of interest in them is the ease with which these can be manipulated to suit the needs of a particular reaction. Most of the properties that are attributed to reaction solvents can be redesigned to reduce or eliminate the losses in solvents and the reaction path can be modified to optimize reactions. This can be useful in recovering and reusing