Aerobic Baeyer–Villiger oxidation of ketones to corresponding esters was performed using metal-free carbon as a solid catalyst and benzaldehyde as the sacrificing agent. Several carbon materials were tested for the oxidation of cyclohexanone to ε-caprolactone, and it was found that Ketjen Black showed the highest catalytic activity, over 90% of ε-caprolactone yield at 50 °C. A catalyst recycling test suggests that the catalyst has high durability under the reaction condition of oxygen atmosphere at 50 °C. Mechanistic study suggests that peracid species produced by a series of chain propagation reactions is the key intermediate, and the carbon catalyst contributes to high aldehyde efficiency by buffering the radical species, which are essential for the chain propagation reactions.

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Hyperbranched polyimide functionalized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was studied as a heterogeneous catalyst for the aerobic oxidation of benzyl alcohol. The catalyst material was synthesized by an A2 + B3 polymerization of pyromellitic dianhydride and 1,3,5-tris(4-aminophenyl)benzene followed by an end-capping reaction with 4-amino-TEMPO. Selective aerobic oxidation of benzyl alcohol to benzaldehyde has been demonstrated using the prepared materials as a catalyst. The recyclability of these materials has been confirmed by recycling tests using the catalyst collected by filtration.