Selective Aerobic Oxidation of Benzylic Alcohols Catalyzed by Carbon‐Based Catalysts: A Nonmetallic Oxidation System

Abstract

Anstelle von Übergangsmetallen kann Kohlenstoff zur selektiven aeroben Oxidation von Benzylalkoholen eingesetzt werden. Das Additiv HNO3 aktiviert einen Kohlenstoffkatalysator mit Nanoschalenstruktur (NSC), der als primäres Oxidationsmittel für den Alkohol dient, und wird durch O2 regeneriert.

A Nitric Acid‐Assisted Carbon‐Catalyzed Oxidation System with Nitroxide Radical Cocatalysts as an Efficient and Green Protocol for Selective Aerobic Oxidation of Alcohols

“…In the absence of AC (run 3), even under heating, nitric acid remained intact. These findings provide further support to our proposed mechanism of NACOS, [6] and more importantly suggest the feasibility of inserting a nitroxide radical-based catalytic cycle into NACOS.…”

“…[17] We also carried out such reactions with NACOS. [6] However, none of those methods match the current approach in terms of aldehyde selectivity at high substrate conversion. Notably, with the addition of active nitroxide radicals, roughly linear reaction curves were obtained, indicating that the reaction rate is independent of substrate concentration.…”

“…The previous NACOS protocol is limited to benzylic alcohols, [6] but with the incorporation of nitroxide radicals, the scope can be expanded to aliphatic alcohols, even under solvent-free conditions. Generally, aliphatic alcohols are less active than benzylic alcohols towards oxidation.…”

“…Very recently, we revealed a novel nitric acid-assisted carboncatalyzed oxidation system, called NACOS. [6] NACOS offers a new non-metallic route for oxygen activation and works well with many different carbon materials, such as nanoshell carbon, activated carbon and carbon black. However, the current scope of NACOS is relatively narrow (i.e., limited to benzylic alcohols), and the selectivity to aldehyde for primary alcohol oxidation is somewhat dependent on the structural features of the carbon catalyst and the substrate concentration.…”

Activation of Dioxygen by Cobaloxime and Nitric Oxide for Efficient TEMPO‐Catalyzed Oxidation of Alcohols

“…Developing new environmentally benign and highly efficient catalytic technologies for the selective aerobic oxidation of alcohols has attracted much attention to date because of the obvious advantages of dioxygen, such as abundance, low cost and non-toxic by-product (H 2 O). [1] Currently, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives have emerged as widely investigated catalysts for the aerobic oxidation of alcohols to the corresponding carbonyl compounds due to its high efficacy and selectivity. [2] However, owing to the inertness of dioxygen, TEMPO alone cannot directly catalyze the oxidation of alcohols with dioxygen as the terminal oxidant, so it always relies on the assistance of various cocatalysts which play the important roles of activating dioxygen and transferring its oxidizability to the next redox cycle of TEMPO.…”