The synthetic routs are greatly related to the structures and composition of ILs, such as metathesis, protic synthesis, halogen free synthesis and other special methods, in this review, the synthesis procedures are summarized into one step method, two step method, enhanced methods and others especial methods, such as the synthetic method of chiral ILs.

1. One step method

The ILs synthesized in one step method are mainly produced by the nucleophilic solvents reacting with the alkyl halide or esters, and the tertiary amine neutral­ized with acid. For example, the alkylimidazole halide, quaternary ammonium halide, alkyl sulfate, alkyl phosphate and neutralization reaction [27—31]. The alkylimidazole based ILs are synthesized according to Eq. 1.1.

2. Two step method

In the two step method, the alkylimidazole halide was first synthesized, then the halide was changed to targeted anions by complex reaction, metathesis reaction, ions exchange and electrolytic method. Many common used ILs are produced with this method, for examples, the [Bmim][FeCl3], [Bmim][PF6], [Bmim]2[SO4] and [bpy][NO3] [32—36]. The synthetic routs are shown in the Eq. 1.2.

MY/HY

R

Lewis Acid N ® N. [MXy+l]

3. Enhanced methods

In the synthesis process, microwave or ultrasonic are used to enhance the reaction to increase the reaction and conversion rate. For example, the [Bmim] [BF4] is synthesized in the route as shown in Eq. 1.3 [37].

4. The synthetic method of chiral ILs [38, 39]

Chiral ILs have more unique properties than that of common ILs, which combining the advantages of chiral material and ILs, and the chiral materials or asymmetric synthesis are both used in the procedure. For example, the chiral

compound (1S, 2R)-(+)-N, N-dimethylephdrinium cation(Fig. 1.1) can be used to synthesized ephedrinium based chiral ILs [39], and the nicotine based chiral ILs are synthesized according to the Eq. 1.4 [40, 41].

Now ILs are applied in a variety of fields, so many companies that produce and sale ILs are occurred all over the world. The common companies that produce ILs are listed in Table 1.3.