Halogenation of Imidazolium Ionic Liquids. Thermodynamics Perspective

TL;DR

This study thermodynamically analyzes fluorination and chlorination of imidazolium cations, identifying favorable halogenation sites and temperature effects to guide ionic liquid functionalization.

Contribution

It provides a comprehensive thermodynamic analysis of halogenation sites on imidazolium cations, which was previously unexplored.

Findings

Halogenation of all carbon atoms is thermodynamically feasible.

The most favorable halogenation site is the first methylene group of the alkyl chain.

The least favorable site is the carbon of the imidazole ring.

Abstract

Imidazolium cations are promising for anion exchange membranes, and electrochemical applications and gas capture. They can be chemically modified in many ways including halogenation. Halogenation possibilities of the imidazole ring constitute a particular interest. This work investigates fluorination and chlorination reactions of all symmetrically non-equivalent sites of the imidazolium cation. Halogenation of all carbon atoms is thermodynamically permitted. Out of these, the most favorable site is the first methylene group of the alkyl chain. In turn, the least favorable site is carbon of the imidazole ring. Temperature dependence of enthalpy, entropy, and Gibbs free energy at 1 bar is discussed. The reported results provide an important guidance in functionalization of ionic liquids in search of task-specific compounds.