Enantioselective liquid-liquid extraction of valine enantiomers in the aqueous two-phase system formed by the cholinium amino acid ionic liquid copper complexes and salt

Abstract

It was widely reported that the heterocyclic ionic liquids (ILs) had relatively high biotoxicity and the cholinium amino acid ionic liquids (ChAAILs) were much environmentally friendly. Therefore, the ChAAILs/salt aqueous two-phase systems (ATPSs) were developed for the chiral resolution of valine enantiomers in this study. The copper complexes were prepared by ChAAILs and Cu(Ac)2, which can be used as both the phase-forming components and the chiral selectors. A series of factors affecting the enantioseparation result were investigated, including type and concentration of ChAAILs, molar ratio of ChAAIL and Cu(Ac)2, type and concentration of salt, concentration of valine, and operation temperature. The valine enantiomers were preferentially recognized in the ChAAIL-rich phase (top phase) and the maximum e.e. value of 55.6% was obtained in the top phase. This ATPS used for the enantioseparation of valine enantiomers has the advantages of environmental friendliness, high enantioseparation efficiency and simple operation by one step extraction.