Abstract
The process of selective oxy-functionalization of hydrocarbons using peroxide, O3, H2O2, O2, and transition metals can be carried out by the reactive oxygen species such as hydroxyl/hydroperoxyl radical and/or metal oxygenated species generated in the catalytic reaction. Thus, a variety of mechanisms have been proposed for the selective catalytic oxidation of various hydrocarbons including light alkanes, olefins, and simple aromatics by the biological metalloproteins and their biomimetics either in their homogeneous or heterogeneous platforms. Most studies involving these metalloproteins are Fe or Cu monooxygenases. The pathways carried out by these metalloenzymes in the oxidation of C–H bonds invoke either radical reaction mechanisms including Fenton's chemistry and hydrogen atom transfer followed by radical rebound reaction mechanism or electrophilic oxygenation/O-atom transfer by metal-oxygen species. In this review, we discuss the metal oxide nano-catalysts obtained from metal salts/molecular precursors (M = Cu, Fe, and V) that can easily form in situ through the oxidation of substrates using H2O2(aq) in CH3CN, and be facilely separated from the reaction mixtures as well as recycled for several times with comparable catalytic efficiency for the highly selective conversion from hydrocarbons including aromatics to oxygenates. The mechanistic insights revealed from the oxy-functionalization of simple aromatics mediated by the novel biomimetic metal oxide materials can pave the way toward developing facile, cost-effective, and highly efficient nano-catalysts for the selective partial oxidation of simple aromatics.
Highlights
The technology of “advanced oxidation processes” essentially applies Fenton’s chemistry for wastewater treatment (Andreozzi et al, 1999; Pignatello et al, 2006)
The study provides an efficient strategy that accumulates active Fe, Cu, and V oxide species of organic–inorganic hybrid nano-catalysts, respectively, through the addition of 35% H2O2(aq) to the Fe/Cu perchlorate and VCl3 in CH3CN for the selective oxidation of simple aromatics (Ramu et al, 2017; Wanna et al, 2019a,b). These metal nanoparticles can be further recycled several times that can carry out the selective catalytic oxidation of benzene to PhOH or p-BQ and toluene to cresols/methyl-p-BQ or benzyl alcohol/benzaldehyde
CH3CN is a polar solvent that can be miscible with polar H2O2 and H2O as well as the non-polar aromatic substrates, leading to oxygenate formation
Summary
The technology of “advanced oxidation processes” essentially applies Fenton’s chemistry for wastewater treatment (Andreozzi et al, 1999; Pignatello et al, 2006). The NIH-shift ratios obtained from the deuterated p-cresol products was 54%, which displayed that the solid-state surface of copper nanoparticles can in general oxidize ortho- or para- (sp2) C–H bonds of toluene via the formation of arene oxide intermediate followed by an NIH rearrangement process.
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