Crystallization of enantiomers

Pure enantiomers are of large interest for several industries. Chemical synthesis is frequently not selective and provides racemic mixtures causing a large interest in efficient separation processes. Preparative chromatography is nowadays a powerful and flexible but expensive technology. As an alternative there exists the possibility to apply cheaper crystallization processes. Based on classifying enantiomeric systems according to their type of solid–liquid equilibria, crystallization processes will be discussed which are capable to provide pure enantiomers. Two separation problems studied in our laboratory will be considered for illustration. Preferential crystallization was used to separate racemic threonine dissolved in water. Cooling crystallization was applied to separate a non-racemic solution of mandelic acid enantiomers dissolved also in water.