Monosubstituted Imidazolium-Based Ionic Liquids

Among the numerous imidazolium-based ionic liquids, monosubstituted imidazolium-based ionic liquids have relatively few applications. The reason is that the stability of the monosubstituted imidazole ring is not high, and the hydrogen on the nitrogen is easily affected by the environment. Moreover, the introduced groups are limited, and the controllability is not strong. However, monosubstituted imidazolium-based ionic liquids also have an irreplaceable position. First of all, its steric hindrance effect is small and the hydrogen bond effect is strong, and it can be used as a reaction medium in organic synthesis. Secondly, it has strong coordination ability and can be used for separation and purification. Finally, it has a lower viscosity and can be used as an electrolyte.

Figure 1. The general structural formula of monosubstituted imidazolyl cations

Applications:

• Organic synthesis: The monosubstituted imidazolium-based ionic liquid retains hydrogen on a nitrogen atom, increases the hydrogen bonding and dipole-dipole interaction between the cation and the reactant, thereby enhancing its ability to dissolve the reactant. In reduction reactions, oxidation reactions, Friedel-Crafts reactions and cross-coupling reactions, which require the use of metal catalysts, monosubstituted imidazolium-based ionic liquids can make two-phase immiscible systems mutually dissolve into a homogeneous reaction and increase the reaction speed, shorten the reaction time and increase the reaction yield.
• Separation and purification: In the field of separation and purification, the green and pollution-free ionic liquids have always been recognized. Sewage contains many organic compounds that cannot be easily removed by precipitation. Such compounds can be removed by extraction and separation with certain solvents. Monosubstituted imidazolium-based ionic liquids have fewer groups and are not prone to chemical reactions. And the strong hydrogen bond and possible coordination effect can increase the solubility of organics, so as to achieve the effect of separation and purification.
• Electrolyte: Ionic liquid has the advantages of inherent ionic conductivity, non-volatile, non-flammable and explosive, and wide electrochemical window. Through the modification of some functional groups, functionalized ionic liquids can be used in a wider range of electrochemical fields. Monosubstituted imidazolium-based ionic liquids generally only contain functional groups such as alkyl groups, are not prone to chemical reactions, and have low viscosity, which can be used as an excellent electrolyte for electricity.

Reference

• J.F. Vélez, L.V. Álvarez, C. del Río, B. Herradón, E. Mann, E. Morales. Imidazolium-based Mono and Dicationic Ionic Liquid Sodium Polymer Gel Electrolytes [J]. Electrochimica Acta 2017, 241, 517-525.