This article introduces the synthesis of ionic liquids. Visit https://www.alfa-chemistry.com/products/ionic-liquids-148.htm for more information.

1. Synthesis of Ionic Liquids
The ionic liquid is in a liquid state at or near room temperature and is a salt composed entirely of
anions and cations, also referred to as a low temperature molten salt. Most salts composed of
anions and cations are generally ionic compounds with strong forces. If the force between the
ions of the ionic compound is broken or weakened, the ionic compound can be liquid at room
temperature or below, so that it is called an ionic liquid. Ionic liquids can be mainly divided into
ammonium ionic liquids, imidazolium ionic liquids, morpholinium ionic liquids, phosphonium
ionic liquids, piperidinium ionic liquids, pyridinium ionic liquids, pyrrolidinium ionic liquids and so
on. Ionic liquids can be synthesized by several methods: one-step synthesis, two-step synthesis,
and other methods including microwave-assisted synthesis and ultrasonic-assisted synthesis.
1 One-step synthesis
The one-step synthesis method refers to a method of synthesizing an ionic liquid in one step
directly by an acid-base neutralization reaction or a quaternization reaction. The method is
simple and convenient to operate has high atomic utilization. The product obtained by this
method is easy to purify and has no by-products. For example, an ionic liquid of nitroethylamine
is prepared by neutralization of ethylamine with nitric acid.
2 Two-step synthesis
The two-step synthesis involves the synthesis of a quaternary ammonium halide salt and the
exchange of a halide anion. Taking an imidazolium salt ionic liquid as an example, a halogen salt
containing a target cation ([cation] X-type ionic liquid) is first obtained by quaternization, and
then the X-ion is replaced with a target anion Y- to obtain a desired ionic liquid.
3 Other synthetic methods
If the ionic liquid is synthesized by heating, an organic solvent is required, which will cause
environmental pollution, and the reaction time is long and the yield is low, so this method is
generally not used. Other synthetic methods include microwave enhancement, ultrasonic
enhancement, and electrochemical method. Microwave-assisted and ultrasonic-assisted ionic
liquid synthesis eliminates the need for organic solvents, reduces pollution during the synthesis
process, speeds up the reaction and increases product yield and purity.
3.1 Microwave-assisted synthesis:
The synthesis of almost all common alkyl imidazoles and alkylpyridine ionic liquids can be carried
out using a commercial microwave reaction system, and the reaction time can be greatly
shortened, and the yield is not lower than the conventional synthesis method. However, the
microwave assisted method is prone to side reactions while significantly shortening the reaction
time. Moreover, microwave reactors are expensive, so this method can only be limited to
small-scale synthesis in the laboratory, and is difficult to use for large-scale industrial production
of ionic liquids.
3.2 Ultrasonic-assisted synthesis:
The results of research of ultrasound-assisted synthesis of ionic liquids show that this method can
also significantly shorten the reaction time without reducing the yield. At present, the research

2. on ultrasonic-assisted synthesis of ionic liquids is mainly the synthesis of common alkyl
imidazoles and alkylpyridine ionic liquids, such as the synthesis of 1-butyl-3-methylimidazolium
fluoroborate. Ultrasonic-assisted synthesis of ionic liquids has the advantages of simple synthesis
conditions, short reaction time, low energy consumption and easy purification of products.