Ester Functionalized Ionic Liquids

The ester group is introduced into the side chain of the cation of the ionic liquid to obtain an ester group functionalized ionic liquid. In ester functionalized ionic liquids, cations are introduced into the side chains of pyridine and imidazole nitrogen atoms from ester groups, and ionic liquids with different properties can be obtained by introducing ester chains of different chain lengths. When the anion is generally BF₆^- or PF₆^-, the ester-based functionalized ionic liquid has better stability. Ester functionalized ionic liquids have higher density, viscosity, glass transition temperature, lower acid value, and water absorption. The functionally changed properties of these ester groups make this ionic liquid widely used in the petrochemical industry.

Figure 1. Common structure of ester functionalized ionic liquids

Applications:

• Polymer electrolyte: The ester functional group facilitates the complexation and dissociation of carrier ions, thereby improving the ionic conductivity of the polymer electrolyte. The ionic liquid itself has excellent electrical conductivity, and the ester functionalized ionic liquid can further improve the electrical conductivity, reduce the activation energy, and increase the thermal stability.
• Lubricant: Ionic liquids, as an easy-to-functional green, high-performance new lubricant, have been widely used on the surface of various friction pairs such as metals and metals, metals and oxides, and metals and ceramics. The introduction of ester groups enhances its anti-friction and anti-wear performance and high load-bearing capacity. Even under high load, the adsorption film formed by the ester functionalized ionic liquid on the metal surface is very stable. And it will not damage the surface of the material.
• HPLC stationary phase: Ionic liquids have high stability and low vapor pressure, and are widely used as stationary phases for chromatographic columns. The ester functionalized ionic liquid is bonded to silica gel to provide multiple forces, such as hydrophobicity, hydrogen bonding, and dipole-induced dipole interaction. In normal phase or reverse phase chromatography, it shows good separation selectivity for phenols and organophosphorus pesticides.

Reference

• Trupti Nirmale,Nageshwar Khupse,Rohitkumar Gore,Jalindar Ambekar,Milind Kulkarni,Anjanikumar Varma,Bharat Kale. Ethoxy-Ester Functionalized Imidazolium based Ionic Liquids for Lithium Ion Batteries[J]. ChemistrySelect 2018, 3, 6255-6261.