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Resolutions of racemates by crystallization : additives and attrition

(2009) Leeman, Michel Sebastiaan

Although biological processes in simple bacteria or rather complex animals such as humans exclusively form left or right-handed molecules, in a normal chemical reaction, carried out in a laboratory, equal amounts of left and right-handed molecules (racemic mixture) are formed. These mirror image molecules (enantiomers) are recognized by the human body in several ways. One enantiomer may have the desired effect whereas the other is inactive. It can, however, sometimes be very toxic. For the pharmaceutical industry it is, literally, often of life or death importance that only the desired enantiomer is put in a medicine. To achieve this, the racemic mixture must be separated. This separation is frequently performed by a crystallization method invented by Louis Pasteur, halfway the 19th century.
In this thesis, techniques are described that can improve the separations of enantiomers by crystallization. By adding small quantities of additive, the yield of the desired pure enantiomer could sometimes be improved considerably. A dramatic discovery was that some racemates can be separated, in a crystallization process from solution, by simply grinding the first formed crystal and at the same time keeping the solution racemic. In this way only one of the enantiomers was obtained in high yield.

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