Chapter 2 - A complete study on the synthesis of ionic liquids

Abstract

Since the discovery of ionic liquids they have been found to be relevant in resolving some of the current problems facing society. This is by virtue of their unique physicochemical and biological characteristics, emerging as an efficient, and environmentally benign alternative resource to volatile organic solvent. The growing demand for ionic liquids has called for the need to establish standard synthetic methods to ensure reliability in the quality of the ionic liquids. Notably, the availability of different types of cations and anions provides the means to easily design certain ionic liquids for application to a specific task at hand. The purpose of this chapter is to review various synthesis methods and strategies needed to obtain ionic liquids. Within this concept the various classes of cations and anions used for the synthesis of ionic liquids are discussed. Synthesis methods such as quaternization reaction, anion exchange by metathesis and ion exchange resin as well as microwave irradiation synthesis are thoroughly discussed. In addition, the direct synthesis route to obtaining halide free ionic liquids by means of N-heterocyclic carbene (NHC) intermediates, as well as phosphorus or sulfur-based direct reactions with imidazoles are reviewed. Furthermore, the synthesis of functionalized ionic liquids are presented. Finally, an overview of the impurities found in ionic liquids and their methods of identification are mentioned.