Ether Functionalized Ionic Liquids

The ether bond is introduced into the side chain of the cation of the ionic liquid to obtain an ether functionalized ionic liquid, which is widely used in the fields of catalysis science, separation technology, electrochemistry and the like. Common ether functional groups include short-chain ether bonds such as methoxymethyl (—CH₂OCH₃) and methoxyethyl (—CH₂CH₂OCH₃), and long-chain ether groups such as alkoxymethyl (—(CH₂)_nOCH₃). As the ether-based chain lengthens, the electron donating effect gradually weakens, and the ether-based group tends to approach the alkyl chain, which will weaken the ether-based functionalization effect. Therefore, ether functionalized ionic liquids generally incorporate short-chain ether groups.

Figure 1. Common structure of ether functionalized ionic liquids

Applications:

• Adsorbing SO₂: The oxygen atom in the ether functional group can form a strong electrostatic interaction with the S in SO₂. The absorption process of SO₂ is physical absorption, and it is easy to desorb and can be recycled. Therefore, the introduction of ether functional groups into the ionic liquid can increase the physical absorption of SO₂ by the ionic liquid and solve the problem of difficult SO₂ desorption.
• Electrolyte: The ether group has a unique electron donating effect, which can effectively reduce the melting point and viscosity of the ionic liquid, while ensuring that the thermal and electrochemical stability of the ionic liquid does not decrease. Therefore, the ether functionalized ionic liquid can be used as a series of low-viscosity, high-conductivity electrolyte additives, so that the battery can obtain high conductivity and good cycle performance.
• Catalyst: The ether functionalized ionic liquid has high catalytic activity in catalyzing the esterification reaction and the alkylation reaction, can promote the reaction to proceed under mild conditions, and has a good repeated use effect.
• Liquid-liquid extraction separation: In product production, purification, and separation and analysis of environmental pollutants, liquid-liquid extraction separation technology has the advantages of simple and fast operation, high recovery rate, and high accuracy. In order to eliminate pollution from the source, green ionic liquids are widely used. Compared with conventional ionic liquids, ether functionalized ionic liquids have the advantages of hydrophilicity and low melting point, and can be used as a two-phase aqueous system to achieve the extraction and separation of proteins and carbohydrates.

Reference

• Frederik Philippi, Daniel Rauber, Björn Kuttich, Tobias Kraus, Christopher W. M. Kay, Rolf Hempelmann, Patricia A. Hunt, Tom Welton. Ether functionalisation, ion conformation and the optimisation of macroscopic properties in ionic liquids[J]. Phys.Chem.Chem.Phys. 2020, 22, 23038-23056.