Kinetics of chiral resolution in stirred crystallization of D/L-glutamic acid

Abstract

Stirred crystallization of racemic (D/L)-glutamic acid (Glu) in the presence of small amounts of L- or D-lysine (Lys) was studied for the effect of transient chiral resolution by monitoring the time evolution of optical rotation and the concentration of the solution. The presence of a small amount of L- or D-Lys retards the crystallization rate of the corresponding enantiomer of Glu in a chirally selective manner, giving rise to transient optical resolution of racemic Glu during crystallization. The optical rotation of the Glu solution was found to increase from zero to a value corresponding to an enantiomeric excess (ee) of 22–35% and subsequently decreases to zero over a period of many hours. During this process, the ee of the crystallized Gu is nearly 100% during the first 35 min and then it decreases slowly to zero. Our results indicate that the time at which the ee of the solution reaches its maximum and the maximum value of the ee show a nonlinear dependence on the initial mole fraction of the chiral impurity. The effect of the impurity is highly chirally selective, indicating “molecular recognition.” Chirality 11:343–348, 1999. © 1999 Wiley-Liss, Inc.