Browsing by Author "Janmanchi, Damodar"

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An efficient and recyclable copper nano-catalyst for the selective oxidation of benzene to p-benzoquinone (p-BQ) using H2O2(aq) in CH3CN
(2019-02-01)
Wanna, Wondemagegn Hailemichael
;
Ramu, Ravirala
;
Janmanchi, Damodar
;
Tsai, Yi-Fang
;
Thiyagarajan, Natarajan
The molecular copper complex tetrakis(acetonitrile)copper(I) perchlorate [Cu(CH3CN)(4)ClO4] (1) was shown to act as a catalyst precursor for the efficient oxidation of benzene to p-benzoquinone (p-BQ) with a percentage selectivity of 60-80% under mild conditions, and produces phenol (PhOH) as a minor product at room temperature. Here, we obtained evidences showing the formation of copper based nanoparticle catalyst (NC) (2) from 1 to be the vital step responsible for its ability to catalyze the conversion of benzene to p-BQ presumably via double oxidation. Addition of a considerable amount of H2O to the reaction mixture improved the selectivity for forming p-BQ to 84% and/or the conversion efficiency to 98%. In addition, the copper NC easily formed in situ through the oxidation of substrate using H2O2 in CH3CN. After separating the NC from the reaction mixture and recycling them several times, it still maintained comparable catalytic efficiency and selectivity for the conversion of benzene to p-BQ. (C) 2019 Elsevier Inc. All rights reserved.
Mechanistic study for the selective oxidation of benzene and toluene catalyzed by Fe(ClO4)(2) in an H2O2-H2O-CH3CN system
(2017-11-01)
Ramu, Ravirala
;
Wanna, Wondemagegn Hailemichael
;
Janmanchi, Damodar
;
Tsai, Yi-Fang
;
Liu, Chih-Cheng
Iron(II) perchlorate in an H2O-H2O2-CH3CN mixture was used to efficiently carry out C-H bond activations of benzene to form phenol and/or hydroquinone, and of toluene to form benzaldehyde, benzyl alcohol, o-cresol, p-cresol, and/or methyl-p-benzoquinone. The reactions were facilely tuned and controlled to selectively yield either a single or double oxygenation of benzene as well as a sp(3) or sp(2) C-H bond oxidation of toluene. On the basis of HAD kinetic isotope effect data, we determined the aromatic oxidation to mostly proceed by way of formation of an arene oxide or a sigma-complex intermediate from high-valence iron species and to then undergo a 1,2-hydride shift, i.e., NIH-shift rearrangement. (C) 2017 Elsevier B.V. All rights reserved.
Selective catalytic oxidation of benzene to phenol by a vanadium oxide nanorod (V-nr) catalyst in CH3CN using H2O2(aq) and pyrazine-2-carboxylic acid (PCA)
(2019-12-07)
Wanna, Wondemagegn Hailemichael
;
Janmanchi, Damodar
;
Thiyagarajan, Natarajan
;
Ramu, Ravirala
;
Tsai, Yi-Fang
Vanadium based catalysts are known to be highly efficient for oxidation reactions using O-2 and/or H2O2. In this study, we developed a vanadium catalyst that can be prepared by a reaction of VCl3 in acetonitrile with the addition of 35% hydrogen peroxide (H2O2). The catalyst was further characterized by a variety of methods including V-51 NMR, XRD, XPS, XAS, EA, ICP-AES, BET, SEM and TEM. Based on the results obtained, the catalyst was identified as a vanadium oxide material (V-nr) with the morphology and shape of a nanorod with dimensions of similar to 40 nm x 450 nm (width x length). The porosity of a material can be essential for small molecule activation on a heterogeneous surface. This material exhibits exceptional catalytic performance for the selective oxidation of benzene to phenol (PhOH) at room temperature using H2O2 as an oxidant in acetonitrile. The addition of pyrazine-2-carboxylic acid (PCA) as a co-catalyst can efficiently enhance the catalytic activity with a percentage selectivity of 87-99% phenol, producing p-benzoquinone (p-BQ) as a minor product. With the deployment of (H2O2)-O-18, we observed the product phenol to be highly enriched by O-18, indicating that the hydroperoxovanadium intermediate is essential for its catalytic conversion. Together with its high NIH shift ratio (80% deuterium remained) observed with the mechanistic probe of 4-[H-2(0,1)] toluene, the results suggested that the catalytic oxidation reaction mediated by Vnr may involve metal based oxygenated intermediates for its highly selective catalytic oxidation of benzene to phenol.