Physical Enantioseparation - Preferential Crystallization

Typical examples of obtaining enantiopure compounds by preferential crystalliza- 

Chirality in Drug Research. Edited by Eric Erancotte and Wolfgang Lindner 

Copyright 2006 WILEY-VCH Verlag GmbH Co. KGaA,Weinheim 

There are three crystal modifications of racemic crystals, depending on the difference in strength of the intermolecular interactions between the enantiomeri-cally hetero- and homo-chiral pairs of the racemate the modifications are racemic compound, conglomerate, and racemic sohd solution (Fig. 5.2). Preferential crystallization can only be applied to a conglomerate. However, most racemic crystals are racemic compounds, and conglomerates are very rare (a few percent of racemic crystals in our experience). This means that we have to transform a racemic compound into a conglomerate in order to carry out the enantioseparation of the racemate by preferential crystallization. 

In a similar manner, the racemates shown in Fig. 5.4 could be transformed into the corresponding conglomerates very easily by salt formation with achiral derivatizing agents [6]. These results indicate that salt formation with an achiral derivatizing agent is very effective for the transformation of an acidic or basic racemate into a conglomerate. 

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