There are a large number of ILs that can be produced theoretically, while the synthesized and reported ones are very limited [25]. By the end of 2009, more than 1,800 available ionic liquids which were composed of 714 different cations and 189 different anions have been reported in the book named ionic liquid: physico­chemical properties have reported [26]. According to our current ionic liquids

Tetraakylammonium

1-phenylethanoyl-3-

methylimidazolium

N-propane

sulfuricpyridiniumdihydro 1-methyl-4-(2-azidoethyl)-1, 2, 4-triazolium

database, there are more than 2,300 kinds of ILs, including varieties of 229 anions, 907 cations. In these ILs, the most common used cations are imidazolium, pyridinium, piperidinium, tetraalkylphosphonium, tetraalkylammonium, trialkylsulfonium and metal based, functional cations, the cations are listed in Table 1.1.

However, the generally used ions are either inorganic or organic, for example, hexafluorophosphate, bis (trifluoromethylsulfonyl) imide, tetrafluoroborate, trifluoro- methanesulfonate, dicyanamide, halide, formate, acetate, and alkyl-phosphate and so on (Table 1.2).

F— в—— F

F

OMe

10 Tyrosine

11 Valine

12b Tetrakis [3, 5-bis (trifluoromethyl)

phenyl] borate

13c bis(trifluoromethanesulfonyl)amide

14 Trifluoroacetate

15d AlCl4- a the methyl also could be changed into ethyl et al.

b the other borate and borane anions are fluoroacetoxyborate, bis(oxalato)borate, alkyl carborane et al. c the similar anions are bis(perfluoroethylsulfonyl)amide, 2,2,2-trifluoro-N-( trifluoromethanesulfonyl) acetamide, tris(trifluoromethanesulfonyl)methanide. d the similar metal salts based anion like FeCl4-.