High resolution of racemic phenylalanine with dication imidazolium-based chiral ionic liquids in a solid-liquid two-phase system

- A series of new dication imidazolium-based chiral ionic liquids were synthesized.
- Novel solid-liquid two-phase systems based on the chiral ionic liquids were developed.
- Excellent effect on enantiomeric separation of racemic phenylalanine was achieved with e.e. 99.2% and yield 85.2% for L-enantiomer in solid phase.
- The separation process is characteristic of no organic solvent, simple operation and fast separation process.

A novel solid-liquid two-phase system was developed for the chiral separation of racemic phenylalanine with new dication imidazolium-based chiral ionic liquids. Preliminary experiments showed distinct enantioselectivity in amino acid extraction with the novel solid-liquid two-phase system, more L-enantiomer of amino acid cooperatively interacted with ionic liquids and copper ions to be the solid phase. Various factors, including the alkyl chain length of cations of ionic liquids, the amount of copper acetate, the ratio of n(ILs)/n(Cu2+), the amount of water and racemic phenylalanine, the resolution time together with the resolution temperature, were systematically investigated for their influence on resolution efficiency. The results showed that, under a certain condition, the enantiomeric excess value and the yield of phenylalanine in liquid phase (mainly containing D-enantiomer) were 67.8% and 96.5%, the enantiomeric excess value and the yield of phenylalanine in solid phase (mainly containing L-enantiomer) were 99.2% and 85.2%. Finally, 2D NMR technology, infrared spectroscopy and molecular simulation method were used to study the interaction mechanism. The results indicated that L-enantiomer of phenylalanine interacts more strongly with chiral ILs and Cu2+. The novel system has characteristics of free-organic solvent, simple operation, fast separation process and very high resolution efficiency for racemic phenylalanine. This work could provide a new and alternative resolution approach for other chiral separations.