Chiral Separation of 3,5-Dinitrobenzoyl-(R,S)-Leucine in Process Intensified Extraction Columns

The countercurrent liquid–liquid extraction of racemic 3,5-dinitrobenzoyl-(R,S)-leucine (DNB-(R,S)-Leu) was experimentally investigated using a process intensified extraction column (PIEC). This column (Øin = 15 mm; Hac = 1100 mm), in which both stirring and pulsation are applied, allows for many equilibrium stages and enables a good separation. DNB-(R)-Leu was obtained with an enantiomeric excess of 98.6% and a yield of 93.7%. The other enantiomer DNB-(S)-Leu was measured with an enantiomeric excess of 85.8% and a yield of 98.0%. A backflow model was developed to describe the concentration profile inside the column and the outlet concentrations. The model was experimentally validated and indicates an accurate calculation of the concentrations with an inaccuracy of less than 10%. Finally, the chiral separation of the counter-current extraction in columns is compared to centrifugal extractors with respect to extraction efficiency and productivity.