From alkanolamines to protic alkanolammonium ionic liquids

Abstract

Ionic liquids (ILs) are a unique class of organic compounds that have attracted increased research attention, as evidenced by the growing number of published studies each year. The applications of ILs are extremely diverse from catalysis and organic synthesis to biochemistry and pharmaceuticals. This review focuses on protic ILs containing both ammonium and hydroxyl functional groups in the cation–protic alkanolammonium ionic liquids (PAAILs). PAAILs are readily formed by proton transfer from a Brønsted acid to a Brønsted base. Here, alkanolamines as precursors of PAAILs are discussed in terms of their synthesis and applications. Further, the structural features of PAAILs are presented, which include intermolecular interactions, conformations of hydroxyalkylammonium cations and X-ray diffraction data for more than 200 structures. It is shown that the structural features of PAAILs, in particular the presence of hydroxyl groups and the length of the alkyl chain of the anion, have a significant influence on their physicochemical properties and further aspects of application. PAAILs are shown to be effective as gas adsorbents, biopolymer solvents, catalysts and reaction media, lubricants and corrosion inhibitors, extractants, enzyme’s stabilizers and activators, and others. Data on biological activity, toxicity, biodegradability of PAAILs and factors affecting them are summarized and discussed. The conversion of active pharmaceutical ingredients into PAAILs is a promising approach to enhance their biopharmaceutical properties.