Abstract
Ionic liquids based on different l-amino acids (glycine, l-valine, l-leucine, l-isoleucine, l-histidine, l-methionine, l-tyrosine, l-tryptophan, l-arginine, and l-threonine) and different cations (tetrabutylammonium (TBA), tributylmethylammonium (tBMA), didecyldimethylammonium (DDA), (2-hydroxyethyl)trimethylammonium (choline) (Chol), alkyl(C12-C14) dimethylbenzylammonium (benzalkonium) (BA), dodecyltrimethylammonium (DDTMA), hexadecyltrimethylammonium (HDTMA), octadecyltrimethylammonium (ODTMA) and 1-ethyl-3-methylimidazolium (EMIM)) have been synthesized and characterized by NMR and FTIR. Viscosity, specific rotation, surface activity, thermal stability (TG), and phase transformations (DSC) have been determined and compared with available data. Furthermore, benzalkonium, didecyldimethylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, and octadecyltrimethylammonium amino acid ionic liquids have been shown to exhibit surface activity. The dissolution of cellulose in amino acid ionic liquids (AAILs) composed of various cations was also investigated. Cellulose was only dissolved in EMIM salts of amino acids. In particular, the influence of the cation type on selected physicochemical and spectroscopic properties were discussed. The article is a mini review on amino acid ionic liquids.
Highlights
Ionic liquids have been described as “designer solvents”, and this means that their properties can be adjusted to the requirements of the process
We present a comparison of the physicochemical and spectroscopic properties of several amino acid ionic liquids composed of different cations—tetrabutylammonium (TBA), tributylmethylammonium, didecyldimethylammonium (DDA), (2-hydroxyethyl)trimethylammonium (Chol), alkyl(C12-C14) dimethylbenzylammonium (BA), dodecyltrimethylammonium (DDTMA), hexadecyltrimethylammonium (HDTMA), octadecyltrimethylammonium (ODTMA), and 1-ethyl-3-methylimidazolium (EMIM)
It was found that the balance between the NH and OH form in these ionic liquids depends on the amino acid [29]
Summary
Ionic liquids have been described as “designer solvents”, and this means that their properties can be adjusted to the requirements of the process. In industrial and pharmaceutical chemistry, ionic liquids based on amino acids have many different applications such as an intermediate in the synthesis of peptides, chiral solvents, and absorbents for acid gases [18]. They have proved to be effective catalysts for many reactions, i.e., asymmetric aldol condensation between aldehydes and ketones in the presence of water [19], Diels–Alder reaction, and asymmetric Michael addition [20,21,22]. It was found that the balance between the NH and OH form in these ionic liquids depends on the amino acid [29]
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