title: Separation of non-racemic mixtures of enantiomers: an essential part of optical resolution.
abstract: 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 ee(I)vs. ee(0) curves (ee(I) refers to the crystallized enantiomeric mixtures, ee(0) 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 ee(0)-ee(I) curve did not correlate with the melting point binary phase diagram.
authors.affiliation: Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, H-1521, Budapest, PO Box 91, Hungary.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Faigl
authors.forename: Elemér
authors.initials: E
authors.lastname: Fogassy
authors.forename: Mihály
authors.initials: M
authors.lastname: Nógrádi
authors.forename: Emese
authors.initials: E
authors.lastname: Pálovics
authors.forename: József
authors.initials: J
authors.lastname: Schindler
mesh_terms: D002845:Chromatography / Q000379:methods; D003460:Crystallization; D005590:Fractional Precipitation / Q000379:methods; D004364:Pharmaceutical Preparations / Q000302:isolation & purification*; D044367:Phase Transition; D012492:Salts / Q000737:chemistry; D013237:Stereoisomerism; D044366:Transition Temperature
chemical_list: D004364:Pharmaceutical Preparations; D012492:Salts