Study on the Mechanisms for Baeyer-Villiger Oxidation of Cyclohexanone with Hydrogen Peroxide in Dif

The green and effective Baeyer-Villiger oxidation reaction of cyclohexanone for preparing ε-caprolactone is of particular importance in the synthesis of new polymer materials.We have discussed here several mechanism types of Baeyer-Villiger oxidation of cyclohexanone with H2O2 in different reaction systems.Five main types have been addressed,i.e.:(1)the non-catalyzed reaction type,where the C＝O of ketones is activated by H+,which is electrolytically dissociated from H2O2 and H2O,to improve the capability of C＝O group for accepting the electron pairs;(2)the thermally activated radical reaction type,where the Criegee intermediate is produced via two steps of radical reaction with-OH attack,with much more hydroxyl radicals being excited in the presence of TS-1 zeolite;(3)the Br(o)nsted acid catalysis reaction type,where both O—O moiety and C＝O group could be activated by Br(o)nsted acid;(4)the solid Lewis acid catalyzed C＝O of the substrate activation reaction type through enhancing the donor-acceptor interaction between the antibonding π*c-o orbital of cyclohexanone and HOMO of Sn-containing zeolites;and(5)the solid Lewis acid catalyzed H2O2 to form MeOOH oxidative species by converting the highest occupied molecular orbital(HOMO)of Ti-OOH into a singly occupied molecular orbital(SOMO),making the O—O group highly electrophilic to attack the C＝O of cyclohexanone during the Baeyer-Villiger oxidation process.in the end,we have also compared the different mechanisms and put forward our opinions on the development direction of catalytic materials aiming at eco-friendly Baeyer-Villiger oxidation of cyclohexanone in the years to come.