As an important raw material for the synthesis of polycaprolactone, a significant alternative for the nondegradable plastic, ε-caprolactone (ε-CL) monomer is typically produced through the Baeyer–Villiger oxidation of cyclohexanone (Cy═O). In this work, a solvent-free, highly efficient, and nonmetallic catalytic system was developed to produce the ε-CL monomer with dioxygen as the oxidant and benzaldehyde (BEA) as the co-oxidant. Nitrogen-doped carbon nanotubes (NCNTs) as the catalyst boost the catalytic activity (10.09% conversion, 10.06% yield of ε-CL), much higher than other carbon catalysts. The normalized specific activity of NCNTs reached 2964.80 mmol/g/h and 20.02 mmol/m2/h, which are 2–4 orders of magnitude higher than the state-of-the-art catalysts. The structure-dependent activity result shows that the ratio between pyridine nitrogen (NP) and graphite nitrogen (NG) on the surface of NCNTs positively affects the catalytic performance. Oxygen functionalities on the NCNT surface inhibit the activity by suppressing the auto-oxidation of BEA, which unexpectedly increases aldehyde efficiency. Finally, this process could be scaled up to a molar-scale reaction with a similar activity, which lays down the foundation of the industrial application of the solvent-free Baeyer–Villiger oxidation catalyzed by nanocarbons.
The microbial production of either ester/lactones or enantio-enriched alcohols through Baeyer–Villiger oxidation or stereoselective reduction of ketones, respectively, is possible by using whole cells of A. subglaciale F134 as a bifunctional biocatalyst. The chemoselective pattern of acetophenone biotransformation catalyzed by these cells can be regulated through reaction temperature, directing the reaction either towards oxidation or reduction products. The Baeyer–Villiger oxidation activity of A. subglaciale F134 whole cells is particularly dependent on reaction temperature. Acetophenone was transformed efficiently to phenol via the primary Baeyer–Villiger product phenyl acetate at 20 °C after 48 h with 100% conversion. In contrast, at 35 °C, enantio-enriched ( S )-1-phenylethanol was obtained as the sole product with 64% conversion and 89% ee . In addition, A. subglaciale F134 cells also catalyze the selective reduction of various structurally different aldehydes and ketones to alcohols with 40% to 100% yield, indicating broad substrate spectrum and good enantioselectivity in relevant cases. Our study provides a bifunctional biocatalyst system that can be used in Baeyer–Villiger oxidation as well as in asymmetric carbonyl reduction, setting the stage for future work concerning the identification and isolation of the respective enzymes.
The Sn-Beta zeolite is an efficient Lewis acid catalyst for a wide range of chemical reactions. Here a seed-free aerosol-assisted hydrothermal strategy is used to synthesize plate-like Sn-Beta zeolite with higher tin content. A majority of Sn species were transformed into the framework of Beta zeolite as the desired tetrahedral coordination state, which creates strong Lewis acid sites. Moreover, the diffusion property of the Sn-Beta zeolite can be further improved by a mild base-surfactant (NH 3 ˙ H 2 O-CTAB) treatment. The addition of CTAB can not only narrow the mesopore distribution but also prevent the excessive loss of Sn species. The obtained hierarchical Sn-Beta zeolite exhibits an enhanced catalytic performance in the Baeyer–Villiger oxidation of bulky ketone.
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