Extractive separation of amino acid enantiomers with co-extractants of tartaric acid derivative and Aliquat-336

In our previous work the cationic carrier di(2-ethylhexyl)phosphoric acid (D2EHPA) as one component of co-extractant has been successfully used for the chiral separation of amino acid enantiomers. In this work anionic carrier a quaternary ammonium salt (Aliquat-336) is used instead of D2EHPA, and a derivative tartaric acid (O,O′-dibenzoyl-(2S,3S)-tartaric acid ((+)-DBTA) or O,O′-dibenzoyl-(2S,3S)-4-toluoyl-tartaric acid ((+)-DTTA)) as the chiral selector in the co-extractant. Several factors including extractants compositions, concentration of amino acids, molecular structure and temperature, which influence the co-extraction efficiency of amino acid enantiomers are studied. The obtained results are compared with those using D2EHPA, and the property of the carriers (cationic or anionic) are found to differ in the distribution ratios and enantioselectivities greatly, which is favorable to look for new extractants or select appropriate enantiomers with both high extractive capacities and enantioselectivities. It may also be very helpful to optimize the extraction systems and realize the large-scale production of enantiomer.