Preferential Enrichment and Crystal Structure

Abstract

Comparison of three different stable crystal structures of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylammonium p-nitrobenzenesulfonate [(±)-NNMe₂], and its p-chlorobenzene-sulfonate [(±)-NCMe₂] and p-toluenesulfonate [(±)-NTMe₂] derivatives is described. The first two racemates exhibited the phenomenon of the Preferential Enrichment, but the last one failed to do. It is clear that the nature of the para substituent on the benzenesulfonate group greatly affects the crystal structure and thereby governs the occurrence of the Preferential Enrichment; i.e., substitution by an electron-withdrawing group leads to the formantion of an ordered racemic compound crystal or a fairly ordered racemic mixed crystal of the two enantiomers, while the presence of an electron-donating group results in the formation of a highly disordered racemic mixed crystal.

Key Words:

• preferential enrichment
• enantiomeric resolution
• mixed crystal
• racemic compound
• disorder