Enantioseparation of amino acids by co-extractants with di(2-ethylhexyl)phosphoric acid and tartaric acid derivatives

A co-extraction method using di(2-ethylhexyl)phosphoric acid (D2EHPA) with each of the two tartaric acid derivatives, O,O′-dibenzoyl-(2S,3S)-tartaric acid [(+)-DBTA] and O,O′-dibenzoyl-(2S,3S)-4-toluoyl-tartaric acid [(+)-DTTA] was developed for the enantioseparation of four amino acids: racemic tryptophan (rac-Trp), racemic phenylalanine (rac-Phe), racemic p-hydroxyphenylglycine (rac-Hpg) and racemic tyrosine (rac-Tyr). The extractants were prepared in various proportions and diluted in n-octanol. The influence of the extractant composition, concentration of amino acid enantiomers, molecular structure of the solutes and extractive equilibrium temperature were studied. The maximum enantioselectivities of the four amino acids were 4.02, 1.37, 1.52 and 2.06 for Trp, Phe, Hpg and Tyr, respectively. The effects of the molecular structure of the solutes and amino acids along with the equilibrium temperature on the distribution ratio and enantioselectivity were examined, which is helpful for optimizing the extraction systems and realize the large-scale production of pure enantiomer.