Seeded Crystallization with Racemization SR

We now consider seeding of the S enantiomer along with the racemization reaction for two values of racemization constant, 1 x 10-4 s-1 (SRI) and 1 x 10-3 s-1 (SR2). As can be seen in Fig. 11.9, racemization holds the path closer to a composition of a 50 50 mixture. In addition, the product purity at the end of the batch is significantly higher than in the other cases (Fig. 11.10). Although some of the undesired R enantiomer still crystallizes out, the ratio of the amounts of S to R is significantly higher than the SC case. This is particularly so for the case with fast racemization from R to S. 

In general, purity increases with the amount of seeding and rate of racemization. However, the product purity encounters a plateau when the amount of seeding is in excess of 4 mol% of the amount of S in the mother liquor. These results are for a uniform seed size, and are expected to depend on the particle size distribution of the seed crystals used, although the general trends will remain the same. 

The authors gratefully acknowledge financial support from the Research Grant Council HIA02/03.EG02. 

Horwood, et al., Phthalic Adds, in Kirk Othmer Encyclopedia of Chemical Technology, Vol. 17, 3rd edn., p. 732. John Wiley Sons, 

Wibowo and K. M. Ng, Visualization of High Dimensional Systems via Geometric Modeling with Homogeneous Coordinates, Ind. 

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