The selective oxidation of aniline to metastable and valuable azoxybenzene,a zobenzene or nitrosobenzene has important practical significance in organic synthesis.However, uncontrollable selectivity and laborious synthesis of the expensive required catalysts severely hinders the uptake of these reactions in industrial settings.Herein, we have pioneered the discovery of Zr(OH) 4 as an efficient heterogeneous catalyst capable of the selective oxidation of aniline,u sing either peroxideo rO 2 as oxidant, to selectively obtain various azoxybenzenes,s ymmetric/unsymmetric azobenzenes,a sw ell as nitrosobenzenes,b ys imply regulating the reaction solvent, without the need for additives.M echanistic experiments and DFT calculations demonstrate that the activation of H 2 O 2 and O 2 is primarily achieved by the bridging hydroxyl and terminal hydroxyl groups of Zr(OH) 4 ,r espectively.T he present work provides an economical and environmentally friendly strategy for the selective oxidation of aniline in industrial applications.
The metal-oxide-catalyzed transfer hydrogenation of nitroarenes to anilines by hydrazine hydrate has been widely reported; however, the risk of explosion resulting from excess hydrazine hydrate and high temperatures and complex preparations of these catalysts immensely hinder their industrial application. Herein, we use a simple co-precipitation method to synthesize atomically dispersed Ce-doped α-Fe 2 O 3 (Ce 0.025 -Fe 2 O 3 -350 °C), which can completely reduce nitroarenes using stoichiometric hydrazine hydrate at room temperature, where the parent α-Fe 2 O 3 is inactive. A thorough characterization indicates that the incorporation of Ce into the crystal lattice of α-Fe 2 O 3 reorganizes the electronic structure of the surrounding Fe, such that the Lewis acidity of Fe 2 O 3 is enhanced, which is the key for the room-temperature decomposition of N 2 H 4 •H 2 O. The structure is also beneficial for the adsorption of nitroarene, leading to the weakening of the N−O bonds. Mechanistic experiments and DFT calculations demonstrate that the reduction proceeds through Ph-NO 2 → Ph-NHOH → Ph-NH 2 without the widely recognized Ph-NO intermediate. Moreover, Ce 0.025 -Fe 2 O 3 -350 °C exhibits good stability in a continuous-flow reaction.
The heterogeneous catalytic oxidative coupling synthesis of 2-amino-3H-phenoxazin-3-one (APXO) from the oxidative coupling of 2-aminophenol has important practical significance, due to its significant antiproliferative properties. However, the use of noble metals, alkaline additives, and explosive H 2 O 2 seriously restricts its applicability in industrial settings. Herein, through preparing a cerium-doped manganese oxide catalyst, we achieved the green synthesis of APXOs, using atmospheric oxygen as an oxidant, and without any additives. Its high activity can be attributed to the greatly enhanced oxidation capacity, oxygen activation capacity, and alkalinity that comes from doping with cerium. Remarkably, we found that 2-amino-1,9-dimethyl-3H-phenoxazin-3-one possesses excellent fluorescence properties and could be applied as a fluorescent molecular probe in various detection and labeling studies. This methodology provides an environmentally friendly and economical strategy for the synthesis of APXO in industrial applications, preserving the stability of the heterogeneous catalyst, which showed minimal metal leaching.
The selective oxidation of aniline to metastable and valuable azoxybenzene,a zobenzene or nitrosobenzene has important practical significance in organic synthesis.However, uncontrollable selectivity and laborious synthesis of the expensive required catalysts severely hinders the uptake of these reactions in industrial settings.Herein, we have pioneered the discovery of Zr(OH) 4 as an efficient heterogeneous catalyst capable of the selective oxidation of aniline,u sing either peroxideo rO 2 as oxidant, to selectively obtain various azoxybenzenes,s ymmetric/unsymmetric azobenzenes,a sw ell as nitrosobenzenes,b ys imply regulating the reaction solvent, without the need for additives.M echanistic experiments and DFT calculations demonstrate that the activation of H 2 O 2 and O 2 is primarily achieved by the bridging hydroxyl and terminal hydroxyl groups of Zr(OH) 4 ,r espectively.T he present work provides an economical and environmentally friendly strategy for the selective oxidation of aniline in industrial applications.
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