•c-MWCNTs presented excellent activity in aerobic oxidation ketones.•c-MWCNTs showed good recyclability and reusability.•Mechanism of c-MWCNTs to stabilize the radical species in the reaction.Multi-walled carbon nanotubes (MWCNTs) as metal-free catalysts presented excellent activity and selectivity in the Baeyer-Villiger oxidation of ketones to corresponding lactones in the presence of molecular oxygen and benzaldehyde. Different factors including catalyst, solvents, amount of catalyst were systematically investigated. Compared with MWCNTs, carboxylic multi-walled carbon nanotubes (c-MWCNTs) catalyst exhibited higher performance for the oxidation of ketones, showing good recyclability and reusability. The yield of ε-caprolactone was obtained with 94% under the optimum conditions. Also, c-MWCNTs presented excellent activity towards the oxidation of various cyclic ketones to the corresponding lactones. The introduced carboxyl group on the surface of MWCNTs was favorable to obtain high dispersion in the reaction solution. In addition, the recording of in situ Electron Paramagnetic Resonance (EPR) and Raman spectroscopy indicated that carboxyl group could significantly stabilize the radical species in the reaction.Download full-size imageThe carboxylic multi-walled carbon nanotubes (c-MWCNTs) can act as metal-free catalyst to against the inhibition, which are in favor of the chain propagation reactions to assure of producing peroxybenzoic acid to the oxidation of cyclohexanone.

Generally, gaseous propylene is hard to oxidize directly in liquid phase by dioxygen under mild conditions. Here, the liquid phase epoxidation of propylene to propylene oxide (PO) using molecular oxygen catalyzed by manganese porphyrins (MnTPPCl) in the presence of benzaldehyde was developed. Manganese(III) porphyrin exhibited excellent activity for the selective oxidation of propylene under mild conditions. The conversion of propylene and selectivity towards PO can reach 38% and 80%, respectively. The turnover frequency (TOF) of MnTPPCl catalyst reached 1840 h−1. Experiment evidences that the generation of peroxide and Mn(IV) oxo species during propylene epoxidation occurred, which was confirmed by in situ IR, in situ UV and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). On the basis of the experimental results, the mechanism for the epoxidation of propylene in the presence of metalloporphyrins and benzaldehyde with dioxygen was proposed. The mechanism is also supported by density functional theory (DFT) calculations.