Comparison of Acid Anhydrides with Carboxylic Acids in Enantioselective Enzymatic Esterification of Racemic Methol
外消旋薄荷醇对映选择性酶促酯化中酸酐与羧酸的比较研究

Optical resolution of racemic menthol has been efficiently achieved by lipase catalyzed enantioselective esterification in an organic solvent.The performance of the reaction using an acid anhydride as an acyl donor was compared with that using its corresponding free acid.The reactivities of acid anhydrides were found to be higher than their corresponding free acids,but acid anhydrides were also found easy to be hydrolyzed into free acids under the catalysis of the same enzyme.The existence of too high concentration of an acid anhydride in a micro aqueous reaction system will cause dehydration and thus deactivation of the enzyme,and will enhance non selective esterification of a chiral alcohol,which will reduce the optical purity of the product.All these drawbacks,however,could be effectively overcome in a semi batch reaction system into which propionic anhydride was continuously fed.This system showed some advantages over a batch reaction system using free propionic acid:the reaction time of dl menthol was shortened by half,the stability of the enzyme was much enhanced,and the optical purity of the product ( l menthyl ester) was kept at a similarly high leve(>98%ee).