Continuous Chiral Separation of Amino Acid Derivatives by Enantioselective Liquid−Liquid Extraction in Centrifugal Contactor Separators

The continuous enantioselective liquid-liquid extraction of aqueous 3,5-dinitrobenzoyl-D,L-leucine (DNB-d,l-leu) by a cinchona alkaloid extractant (CA) in 1,2-dichloroethane using a centrifugal contact separator (CCS) was studied at 294 K. Typical concentrations were in the order of 1 mM for both DNB-d,l-leu and CA. The best results were found at a pH of 6, with 61% yield for DNB-l-leu and an enantiomeric excess of 34%. Back-extraction studies at different pH values showed that the host can be recovered efficiently in a single CCS, provided that pH > 9. Experimental studies indicate that the CCS behaves as an equilibrium extraction stage, even at total throughputs exceeding 50% of the equipment capacity (1.9 L min^-1). A previously developed equilibrium stage extraction model was successfully applied to describe the data for both the extraction and the back-extraction experiments.