Chiral resolution of DL-glutamic acid by a chiral additive

BACKGROUND Enantiomerically pure compounds occupy an important position in industrial production of pharmaceuticals, food, chemical engineering, etc. The separation of d and l molecules is an important and challenging task. The 'tailor-made' additive method is a simple and efficient crystallization separation technology. However, according to reports, there is a poor crystal yield when obtaining a relatively ideal enantiopurity and vice versa. Furthermore, the crystallization time always needs to be controlled strictly. RESULTS In this paper, we studied the effect of the amount and kinds of additives, crystal seeds and crystallization time on the purity and yields of crystals. Two strategies involving a chiral additive for the selective crystallization of only d-glutamic acid from a solution of racemic dl-glutamic acid (dl-Glu) are presented. One strategy is based on the addition of sufficient additive (l-arginine or l-phenylalanine with a mole fraction of 40%) and beta-d-Glu crystal seeds, the crystal yield reaching 23-25%. The other relies on carrying out the crystallization twice in the presence of the additive (5 mol%) and the crystal seeds, the yield reaching 30-34%. CONCLUSIONS Two separation methods with a relatively high crystal yield and optical purity were established. The proposed strategies could meet the requirements of both crystal purity and yield on chiral separation, and the separation of d- and l-Glu is nearly perfect. Furthermore, the methods are very easy to operate, and require no hand picking. Most importantly, our methods are barely influenced by the crystallization time. (c) 2021 Society of Chemical Industry (SCI).

Automated summary

Two strategies involving chiral additives for the selective crystallization of d-glutamic acid from dl-glutamic acid solution were presented. One strategy achieved a crystal yield of 23-25% by adding sufficient l-arginine or l-phenylalanine additive and beta-d-Glu crystal seeds. The other strategy achieved a yield of 30-34% by conducting the crystallization twice in the presence of additive and crystal seeds.