Optimizing the Yield of a Pure Enantiomer by Integrating Chiral SMB Chromatography and Racemization. Part 1: Experiments

In this work, we examine the chromatographic purification of the chiral amide N-(2-methyl-benzylidene)-phenylglycine amide (NMPA). Specifically, we find that its adsorption behavior on an AY polysaccharidic chiral stationary phase (amylose tris(5-chloro-2-methylphenylcarbamate)), with acetonitrile as mobile phase, follows an uncommon type-1 mixed Langmuir isotherm. Moreover, we measure the racemization rate of NMPA when polymer-supported 1,8-diazabicycloundec-7-ene (DBU) is used as a catalyst in a fixed-bed reactor. We also determine the system's solid-liquid equilibria at different temperatures. This characterization is necessary for the design of an integrated process where simulated moving bed (SMB) chromatography is combined with racemization for the recycle of the undesired enantiomer. On the basis of the physicochemical properties above, three-column intermittent SMB (3C-ISMB) experiments were run at different concentrations and compositions to prove that an enantiopure product can be obtained when the separation is operated at high feed concentrations (nonlinear chromatographic conditions) in the case not only of a racemic feed but also of nonracemic feeds, which are relevant for the integrated process when racemization is slow, and thus incomplete.ISSN:1520-5045ISSN:0888-588