Syntheses and characterization of the analogues of glycine-betaine based ionic liquids with saccharinate anion: Application in the extraction of cadmium ion from aqueous solution

Abstract

A series of 5 ionic liquids (ILs) based on analogues of glycine-betaine cations [tri(n-butyl)(2-alkoxy-2-oxoethyl)ammonium with linear alkyl chains [n-butyl, to n-octyl] ([Bu3NC2OCn]+, n = 4 to 8) associated to saccharinate anion have been synthesized. These new hydrophobic ionic liquids were characterized using spectroscopic methods (IR, 1H and 13C NMR) and elemental analysis. The effect of alkyl chain length of the cation core on the physicochemical properties of these ionic liquids have been investigated. The extraction ability of these ionic solvents towards aqueous divalent Cd(II) was investigated. It was found that these saccharinate based ionic liquids extract Cd(II) ions with extraction yields up to 96%. The extraction mechanism studied shows that saccharinate ions from the ionic liquid phase is transferring to the aqueous phase, by an anionic exchange with the nitrate counter anion of the cadmium(II) salt and the formation of an insoluble compound between Cd2+ and saccharinate ions corresponding to [Cd(Sac)2(OH2)4]·2H2O complex.