Preparation method of ionic liquid

There are many types of ionic liquids. By changing the different combinations of cations and anions, different ionic liquids can be designed and synthesized. There are basically two basic methods for the synthesis of ionic liquids: direct synthesis and two-step synthesis.

Direct synthesis

The ionic liquid is synthesized in one step through acid-base neutralization reaction or quaternary amination reaction, which is economical and simple to operate, has no by-products, and the product is easy to purify. A series of tetrafluoroborate ionic liquids with different cations were synthesized by the acid-base neutralization method such as Hlrao. In addition, a variety of ionic liquids, such as halogenated 1-alkyl 3-methylimidazole salts, halogenated pyridinium salts, etc., can also be prepared in one step through the quaternization reaction.

Two-step synthesis

The direct method is difficult to obtain the target ionic liquid, and a two-step synthesis method must be used. There are many applications for the preparation of ionic liquids by the two-step method. The preparation of commonly used tetrafluoroborate and hexafluorophosphate ionic liquids usually adopts a two-step method. First, a halide salt containing the target cation is prepared through a quaternary amination reaction; then the target anion is substituted for the halogen ion or Lewis acid is added to obtain the target ionic liquid. In the second step of the reaction, when using metal salt MY (commonly used is AgY), HY or NH4Y, Ag salt precipitation or amine salt, HX gas is easily removed, and strong proton acid HY is added. The reaction requires low-temperature stirring conditions. Then, it is washed with water several times until it is neutral, the ionic liquid is extracted with an organic solvent, and finally the organic solvent is removed in a vacuum to obtain a pure ionic liquid. Special attention is paid to the fact that in the process of exchanging X-(halogen) anions with the target anion Y, the reaction must be as complete as possible to ensure that no x. anions remain in the target ionic liquid, because the purity of the ionic liquid is critical to its The characterization of applications and physico-chemical properties is crucial. The synthesis of high-purity binary ionic liquids is usually prepared by anion exchange using ion exchange resins in an ion exchanger. In addition, by directly combining Lewis acid (MY) with halide salts, [cation][MnXny+l] type ionic liquids can be prepared. For example, the preparation of chloroaluminate ionic liquids uses this method, as described in the properties of ionic liquids. The acidity of the ionic liquid can be adjusted as needed.