Functional ionic liquids as chiral selector for visual chiral sensing and enantioselective precipitate

This work describes a rapid and efficient method for visual chiral recognition by making use of chiral ionic liquids (CILs) based on shikimic acid and D-pipecolinic acid. Cooperation between copper (II) and appropriate solvents resulted in visual enantioselectivity responses of several amino acids and mandelic acid. All the enantiomeric distinguishment could be obtained within 3 min, depending on the difference of colour or solubility. Then, scanning electron microscopy, infrared spectroscopy, ultraviolet spectroscopy, thermogravimetric analysis and elemental analysis were employed to investigate the potential recognition mechanism. The results indicated that chiral recognition was strongly associated with the different stability between D-complex and L-complex. Furthermore, separation was achieved by treating the chiral sensor with racemic compounds. In the case of tryptophan, the proposed method provided good enantiomeric excess values (90.7% in solid phase and 63.2% in liquid phase). Graphical abstract