Asymmetric Transformation of N-Acetyl- Dl -leucine

The asymmetric transformation of N-acetyl-Dl-leucine by a combination of preferential crystallization of a desired isomer and simultaneous racemization of the opposite isomer was studied. The reaction was analyzed in detail and a practical method for the asymmetric transformation was established. A supersaturated solution of N-Ac-Dl-Leu in acetic acid containing catalytic amounts of acetic anhydride was seeded with the crystals of N-Ac-l-Leu and cooled at a rate of 10 °C/h from 100 °C to 40 °C. As a result, almost optically pure N-Ac-l-Leu was obtained in a yield of 70%, based on the original weight of N-Ac-Dl-Leu.