Crystallization and Resolution of cis‐Permethric Acid with Carbon Dioxide Antisolvent

The crystallization and resolution of cis-permethric acid (cPA) with (1R)-1-phenylethanamine (PhEA) as a resolving agent was investigated using the gas antisolvent (GAS) and supercritical antisolvent (SAS) methods. A significant pressure effect on both the yields and diastereomeric excesses of the crystallized cPA–PhEA salts was found in the 100–200 bar range. The pressure effect was found to be related to the structure and dissociation of the salts. Both methods yielded diastereomeric salts with excellent diastereoselectivity (85–95% compared to 74% reported in literature) and a fibrous structure of uniform fiber diameter (500–700 nm).