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Metal-Free Mesoporous SiO2 Nanorods as a Highly Efficient Catalyst for the Baeyer–Villiger Oxidation under Mild Conditions

Xueyao Zhang, Honglei Yang, Guangxue Yang, Shuwen Li, Xiang Wang, Jiantai Ma
ACS sustainable chemistry & engineering 2018 v.6 no.5 pp. 5868-5876
adsorption, atmospheric pressure, catalysts, catalytic activity, cyclohexanones, electron paramagnetic resonance spectroscopy, filtration, free radicals, nanorods, oxidants, oxidation, porous media, silica, surface area, sustainable technology
The development of efficient and environmentally friendly catalysts for oxidative reaction is of great importance in applied catalysis. In this work, a simple and environmentally benign approach for highly selective preparation of ε-caprolactone by oxidation of cyclohexanone has been carried out, which employed metal-free mesoporous silica (mSiO₂) nanorods as catalyst under atmospheric pressure. The metal-free silica catalyst was applied for the first time in the Baeyer–Villiger (B–V) oxidation reaction. It showed efficient catalytic performance for the B–V oxidation of various cyclic ketones and aliphatic ketones with O₂/benzaldehyde as oxidant. The catalyst could be easily separated from the reaction system by filtration and reused several times without significance loss of activity. Moreover, electron paramagnetic resonance (EPR) spectra of the reaction were obtained, indicating the existence of benzoyloxyl radical. The mechanism study of the reaction demonstrated that the super large surface area diluted the concentration of radicals and the adsorption of radicals could protect the radical species from inhibition.