Selective Oxidation of Aromatic Rings

Kholdeeva, Oxana A.

doi:10.1002/9781118754887.ch14

Cited by 5 publications

(5 citation statements)

References 209 publications

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“…In addition, it has already been known that catalytic aromatic hydroxylation with H 2 O 2(aq) is the cause of further oxidation of initially formed phenols and the appearance of tar (Olah et al, 1981;Kholdeeva, 2015). As long as we take into consideration this additional factor in a heterogeneous platform for the metal catalyzed oxidation or the reaction condition for Fenton's chemistry, the accumulated ROS exerted on the oxide surface may not be considered as diffusible radicals anymore.…”

Section: Discussionmentioning

confidence: 99%

Selective Oxidation of Simple Aromatics Catalyzed by Nano-Biomimetic Metal Oxide Catalysts: A Mini Review

et al. 2020

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The process of selective oxy-functionalization of hydrocarbons using peroxide, O 3 , H 2 O 2 , O 2 , 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 H 2 O 2(aq) in CH 3 CN, 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.

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Section: Discussionmentioning

confidence: 99%

Selective Oxidation of Simple Aromatics Catalyzed by Nano-Biomimetic Metal Oxide Catalysts: A Mini Review

et al. 2020

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“…Functionalized benzoquinones (BQ) are frequently occurring structural moieties in a wide range of biologically active compounds. − The selective catalytic oxidation of alkylphenols with atomically efficient, cheap, and readily available oxidants is the most economical and ecological route to the production of vital BQs, in particular trimethyl- p -benzoquinone (TMBQ, vitamin E key intermediate). − Currently, TMBQ is manufactured through the oxidation of 2,3,6-trimethylphenol (TMP) with molecular oxygen in the presence of quasi-stoichiometric amounts of copper chloride . The inherent drawbacks of this process are the formation of Cl-containing byproducts and the need for corrosion-resistant equipment.…”

Section: Introductionmentioning

confidence: 99%

Highly Efficient Catalysts Based on Divanadium-Substituted Polyoxometalate and N-Doped Carbon Nanotubes for Selective Oxidation of Alkylphenols

et al. 2018

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Alkyl-substituted benzoquinones serve as versatile building blocks for a variety of biologically active compounds. In this work, we present an approach for the environmentally benign synthesis of alkyl-p-benzoquinones, in particular trimethyl-p-benzoquinone (TMBQ, vitamin E precursor), which employs aqueous hydrogen peroxide as oxidant and a divanadium-substituted γ-Keggin polyoxotungstate, [γ-PW10O38V2(μ-O)(μ–OH)]4– (V2-POM), immobilized on nitrogen-doped carbon nanotubes (N-CNTs) as heterogeneous catalyst. A series of supported catalysts V2-POM/N-CNTs containing 5–25 wt % of V2-POM and 0–4.8 atom % of N has been prepared and characterized by elemental analysis, N2 adsorption, SEM, TEM, XPS, and FTIR techniques. The catalytic performance of V2-POM/N-CNTs was assessed in the selective oxidation of 2,3,6-trimethylphenol (TMP) with H2O2 under mild reaction conditions (60 °C, MeCN). The presence of nitrogen in the support ensures strong adsorption and molecular dispersion of V2-POM on the carbon surface, leading to highly active and selective heterogeneous catalysts, which do not suffer from metal leaching and can be used repeatedly without loss of the catalytic performance. By application of the optimal catalyst V2-POM/N-CNTs enclosing 15 wt % of V2-POM and 1.8 atom % of N, TMBQ could be obtained with 99% yield and 80% oxidant utilization efficiency. The catalyst demonstrated the truly heterogeneous nature of the catalysis and high turnover frequencies (500 h–1) and space–time yield (450 g L–1 h–1). FTIR and XPS techniques confirmed the stability of V2-POM and N-CNT support under the turnover conditions.

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“…Substituted phenols are important intermediate products in the polymer processing and production of fine chemicals, − while quinones are crucial intermediates in the synthesis of essential vitamins, nutraceuticals, and pharmaceuticals. − During the past decade, a few efficient catalyst systems have been elaborated for the selective oxidation of alkylphenols to quinones using environmentally benign oxidants (O 2 , H 2 O 2 , t BuOOH) . On the contrary, selective oxygenation of aromatic rings of alkylbenzenes remains one of the most challenging transformations in the organic synthesis. − Alkylbenzenes have electron-donating groups that activate the aromatic nucleus toward electrophilic attack, but on the other hand, alkyl substituents are prone to oxidation, which results in poor aromatic oxidation selectivity. Noncatalytic stoichiometric oxidations of arenes with hazardous and toxic reagents, such as CrO 3 , MnO 2 , OsO 4 , and others, are still widely employed in fine organic synthesis. ,,, Such processes produce large amounts of inorganic waste contaminated by organic tars.…”

Section: Introductionmentioning

confidence: 99%

“…Aromatic oxidation of 1,2,4-trimethylbenzene or pseudocumene (PC) to 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, vitamin E key intermediate) is considered as an in posse industrial process . Currently, TMBQ is produced on an industrial scale through oxidation of 2,3,6- and 2,3,5-trimethylphenols (TMP). ,− In contrast to the oxidation of TMP, the direct aromatic oxidation of PC has been scarcely described in the literature . Few noncatalytic procedures with meta -chloroperoxybenzoic acid and a H 2 O 2 /HCOOH mixture as oxidants have been reported.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Regioselectivity of Aromatic Hydroxylation over Divanadium-Substituted γ-Keggin Polyoxotungstate

et al. 2017

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The aromatic hydroxylation of pseudocumene (PC) with aqueous hydrogen peroxide catalyzed by the divanadium-substituted γ-Keggin polyoxotungstate TBA 4 [γ-PW 10 O 38 V 2 (μ-O)(μ-OH)] (TBA-1H, TBA = tetrabutylammonium) has been studied using kinetic modeling and DFT calculations. This reaction features high chemoselectivity and unusual regioselectivity, affording 2,4,5-trimethylphenol (TMP) as the main product. Then the computational study was extended to the analysis of the regioselectivity for other alkoxyand alkylarene substrates. The protonation/deprotonation of TBA-1H in MeCN/tBuOH (1:1) was investigated by 31 P NMR spectroscopy. Forms with different protonation states, [γ-PV 2 W 10 O 40 ] 5− (1), [γ-HPV 2 W 10 O 40 ] 4− (1H), and [γ-H 2 PV 2 W 10 O 40 ] 3− (1H 2 ), have been identified, and the protonation equilibrium constants were estimated on the basis of the 31 P NMR data. DFT calculations were used to investigate the oxygen transfer process from hydroperoxo species, [γ-PW 10 O 38 V 2 (μ-O)(μ-OOH)] 4−(2) and [γ-PW 10 O 38 V 2 (μ-OH)(μ-OOH)] 3− (2H), and peroxo complex [γ-PW 10 O 38 V 2 (μ-η 2 :η 2 -O 2 )] 3− (3) toward the different positions in the aromatic ring of PC, anisole, and toluene substrates. Product, kinetic, and computational studies on the PC hydroxylation strongly support a mechanism of electrophilic oxygen atom transfer from peroxo complex 3 to the aromatic ring of PC. The kinetic modeling revealed that the contribution of 3 into the initial reaction rate is, on average, about 70%, but it may depend on the reaction conditions. DFT calculations showed that the steric hindrance exerted by peroxo complex 3 is responsible for the origin of the unusual regioselectivity observed in PC hydroxylation, while for anisole and toluene the regioselective para-hydroxylation is due to electronic preference during the oxygen transfer from the active peroxo species 3.

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Selective Oxidation of Aromatic Rings

Cited by 5 publications

References 209 publications

Selective Oxidation of Simple Aromatics Catalyzed by Nano-Biomimetic Metal Oxide Catalysts: A Mini Review

Selective Oxidation of Simple Aromatics Catalyzed by Nano-Biomimetic Metal Oxide Catalysts: A Mini Review

Highly Efficient Catalysts Based on Divanadium-Substituted Polyoxometalate and N-Doped Carbon Nanotubes for Selective Oxidation of Alkylphenols

Understanding the Regioselectivity of Aromatic Hydroxylation over Divanadium-Substituted γ-Keggin Polyoxotungstate

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