The Bridge Between Preferential Crystallization and Diastereomeric Salt Formation

The Bridge Between Preferential Crystallization and Diastereomeric Salt Formation 

In the case of the salt of a racemic acid and a racemic amine, six crystal modifications are possible (Table 5.7), while there are three crystal modifications for the salt of a racemic acid or amine with an enantiopure amine or acid (Table 5.8). If the successful enantioseparation of an amine with an enantiopure acid by diastereomeric salt formation is assumed, the diastereomers in Table 5.8 should obviously be more stable than the double salt and pseudo-diastereomer. Then, the diastereomers in Table 5.7 should be more stable than the other crystal modifications. On the other hand, this assumption leads to the conclusion that the solubilities of the diastereomers in Table 5.8 are largely different from each other. This 

Acid Amine Modification Resolution efficiency with  

R = racemic compound, C = conglomerate, D = double salt. Resolution efficiency = yield x e.e. 

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