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Separation of non-racemic mixtures of enantiomers: an essential part of optical resolution

2010; Royal Society of Chemistry; Volume: 8; Issue: 5 Linguagem: Inglês

10.1039/b917564d

1477-0539

Ferenc Faigl, Elemér Fogassy, Mihäly Nógrádi, Emese Pálovics, József Schindler,

Analytical Chemistry and Chromatography

Non-racemic enantiomeric mixtures form homochiral and heterochiral aggregates in melt or suspension, during adsorption or recrystallization, and these diastereomeric associations determine the distribution of the enantiomers between the solid and other (liquid or vapour) phases. That distribution depends on the stability order of the homo- and heterochiral aggregates (conglomerate or racemate formation). Therefore, there is a correlation between the binary melting point phase diagrams and the experimental eeIvs. ee0 curves (eeI refers to the crystallized enantiomeric mixtures, ee0 is the composition of the starting ones). Accordingly, distribution of the enantiomeric mixtures between two phases is characteristic and usually significant enrichment can be achieved. There are two exceptions: no enrichment could be observed under thermodynamically controlled conditions when the starting enantiomer composition corresponded to the eutectic composition, or when the method used was unsuitable for separation. In several cases, when kinetic control governed the crystallization, the character of the ee0–eeI curve did not correlate with the melting point binary phase diagram.