Separation of Enantiomers by Crystallisation

Even for industrial-scale production of optically active amino acids, classical crystallisation technologies may offer an appropriate alternative to enzymatic methods. Either the seeding with one of the enantiomers (e.g. from S-(carboxy-methyl)-(L)-cysteine), or the crystallisation of diastereomeric salts with bases like derivatives of ephedrine or phenylethylamine maybe suitable (Fig. 4.16). 

In this context, chemists at DSM have made interesting observations. They could demonstrate better yields and selectivities for the crystallisation of substance families, rather than pure substances (Dutch Resolution). [65-69] 

A primary disadvantage, namely the maximum yield of 50 %, can in many cases be compensated by subsequent racemisation. Since the development of a diastereoselective crystallisation method is frequently straight forward, this technology stiU claims its competitive and viable role. 

---