Catalytic selective oxidation of aromatic amines to azoxy derivatives with an ultralow loading of peroxoniobate salts

Abstract

This work demonstrated that the tartaric acid-coordinated peroxoniobate salts can be employed as highly efficient catalysts in oxidative coupling of aniline to azoxybenzene under green and very mild conditions. The...

Homogeneous Tungsten Catalysis for Controllable Selective Oxidation of Anilines via the W(O)(η2-O2)2 Intermediate

“…The relationships between reaction conditions and the main product are summarized in Figure 5a. To gain deeper insight into the reaction mechanism, the kinetics of the conversion 1b to AOB (Figure 5b), AB (Figure 5c), or NSB (Figure 5d) in the W-H 2 O 2 system were monitored using 19 F NMR spectroscopy, with p-fluorotoluene serving as the internal standard. The oxidation profiles of 1b to 2b showed no induction period, indicating rapid oxidation of aniline in THF.…”

“…Although hydroxylamine has been postulated as an important intermediate in several scenarios, 17,18,33,34 such species have never been detected in any catalytic aniline oxidation systems. Notably, at an early stage of catalysis, a significant amount of the active intermediate N-phenylhydroxylamine (ArNHOH) was detected according to 19 F NMR spectroscopy. It was gradually consumed after 45 min, likely converting into nitrosobenzene 5b, whose yield reached its maximum at approximately 50 min.…”

“…Through a combination of catalytic experiments and stoichiometric studies, the reactivity of key intermediates, particularly W-2, was thoroughly investigated. The application of 19 F NMR spectroscopy enabled for the first time experimental insights into the mechanistic details of controllable aniline oxidation. Kinetic studies have demonstrated that the origin of selectivity for multiple products arises from the precise conversion of active intermediates, aryl hydroxylamine, and nitrosobenzene into specific products, revealing a correlation between product distribution and the inherent acidity of the solvent.…”

“…The oxidation of inexpensive and readily available anilines to produce highly valuable products (Figure b), such as azoxybenzenes (AOB), − azobenzene (AB), , nitrosobenzenes (NSB), and nitrobenzenes (NB), holds practical importance in industrial and academic fields due to their essential uses in pharmaceuticals, bioactive products, functional materials, and organic dyes. Hydrogen peroxide is considered a green oxidant because its only byproduct is water, offering new possibilities for developing green and sustainable methods.…”