Method for preparing L-oxiracetam crystal form II through ball milling

The invention provides a method for preparing L-oxiracetam crystal form II. The high-purity L-oxiracetam is prepared from S-4-chloro-3-cyclopentyl hydroxybutyrate and sodium azide as starting raw materials; then, the L-oxiracetam prepared by the method is used as raw materials for preparing the L-oxiracetam crystal form II through the matching of isopropanol, grinding frequency and grinding time; the optical purity reaches 99.9 percent or higher; the product quality of the L-oxiracetam crystal form II is greatly improved.