Heterogeneous Catalytic Oxidation of Amides to Imides by Manganese Oxides

Selective α-oxidation of amides via visible-light-driven iron catalysis

Hydroxyl radicals (˙OH) as one of the highly reactive species can react unselectively with a wide range of chemicals. The ˙OH radicals are typically generated under harsh conditions. Herein, we report hydroxyl radical-induced selective N-α C(sp3)-H bond oxidation of amides under greener and mild conditions via an Fe(NO3)3·9H2O catalyst inner sphere pathway upon irradiation with a 30 W blue LED light strip (λ = 455 nm) using NaBrO3 as the oxidant. This protocol exhibited high chemoselectivity and excellent functional group tolerance. A preliminary mechanism investigation demonstrated that the iron catalyst afforded hydroxyl radicals via the visible-light-induced homolysis (VLIH) of iron complexes followed by a hydrogen atom transfer (HAT) process to realize this transformation.

MOF-derived MnO@C with high activity for electric field-assisted catalytic oxidation of aqueous pollutants

The activation of oxygen (O₂) under room condition is important for the utilization of air to perform oxidation. Here, we report a porous carbon-encapsulated MnO (MnO@C) derived from Mn metal-organic framework (MOF)grown in-situ on a graphite felt (GF) support. The MnO@C exhibits superior catalytic activity in an electric field-assisted catalytic oxidation system for the degradation of organic pollutants under room condition. The catalytic oxidation reaction applies a surface reaction pathway in which the surface-bound chemisorbed oxygen species are electro-oxidized and then involved in the oxidation of co-adsorbed organic pollutants. The abundant oxygen vacancies and oxygenated functional groups in MnO@C provide active sites for the chemisorption of O₂, and its conductive mesoporous structure allows facile electrons and mass transfer. As a result, the MnO@C/GF catalyst displays quite high turnover frequency (TOF) value as 0.038 mg-TOC mg-MnO^-1 min^-1, which is 6.66 times higher than that of the MnO/GF catalyst prepared by impregnation method as a comparison. With the aid of + 1.0 V of positive electric field, the catalytic oxidation system exhibits extensive effectiveness in mineralizing a variety of dyes, pharmaceuticals, personal care products, and phenolic compounds under room condition with significantly enhanced biodegradability.

Metal-free photoredox-catalyzed direct α-oxygenation of N,N-dibenzylanilines to imides under visible light

An efficient synthesis of imides using metal-free photoredox-catalyzed direct α-oxygenation of N,N′-disubstituted anilines in the presence of 9-mesityl-10-methylacridinium [Acr⁺-Mes]BF₄ as a photoredox catalyst and molecular oxygen as a green oxidant under visible light was developed. This photochemical approach offered operational simplicity, high atom economy with a low E-factor, and functional group tolerance under mild reaction conditions. Control and quenching experiments confirmed the occurrence of a radical pathway and superoxide radical anion α-oxygenation reactions, and also provided strong evidence for the reductive quenching of [Acr⁺-Mes]BF₄ based on a Stern–Volmer plot, which led to the proposed mechanism of this reaction.

A visible-light-mediated direct α-oxygenation of N,N-dibenzylanilines to imides in the presence of [Acr⁺-Mes]BF₄ as a metal-free photocatalyst and O₂ as a green oxidant.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Lithium promoted mesoporous manganese oxide catalyzed oxidation of allyl ethers

Herein we report the first example of the catalytic aerobic partial oxidation of allyl ether to its acrylate ester derivative. Many partial oxidations often need an expensive oxidant such as peroxides or other species to drive such reactions. In addition, selective generation of esters using porous catalysts has been elusive. This reaction is catalyzed by a Li ion promoted mesoporous manganese oxide (meso-Mn₂O₃) under mild conditions with no precious metals, a reusable heterogeneous catalyst, and easy isolation. This process is very attractive for the oxidation of allyl ethers. We report on the catalytic activity, selectivity, and scope of the reaction. In the best cases presented, almost complete conversion of allyl ether with near complete chemo-selectivity towards acrylate ester derivatives is observed. Based on results from controlled experiments, we propose a possible reaction mechanism for the case in which N-hydroxyphthalimide (NHPI) is used in combination with trichloroacetonitrile (CCl₃CN).

Acrylics and acrylates have become important building blocks for the chemical industry, but their efficient synthesis remains a challenge. Here, the authors report the first example of the catalytic aerobic partial oxidation of allyl ether to its acrylate ester derivative using a Li ion promoted mesoporous manganese oxide under mild conditions.

Oxidation of amine α-carbon to amide: a review on direct methods to access the amide functionality

A number of methods have been adopted for the synthesis of amides; among these methods, the oxidation of an amine to an amide is growing in interest as a means to prepare this imperative functional group.