Amination of Five Families of Room-Temperature Ionic Liquids: Computational Thermodynamics and Vibrational Spectroscopy

Abstract

The amino group is important to enhance carbon dioxide capture capabilities of substances, including room-temperature ionic liquids (RTILs). We report thermodynamics of amination for five organic cations representing different families of RTILs (imidazolium, pyridinium, morpholinium, pyrrolidinium, pyrazolium) and compare all prospective amination sites. We conclude that amination of the cation ring is more favorable than amination of the side chains. Redistribution of electron density due to amination partially correlates with variation of enthalpy and Gibbs free energy, whereas entropic part is similar for all cations and all amination sites. Vibrational frequencies allow for easy distinguishing amination products from reactants and simplify identification of the reaction site (ring or side chain). Formation of strong hydrogen bonds between the amino group and the anions greatly favors amination of RTILs, compared to amination of benzene.