- Copper catalyzed oxidation of tetralin to 1-(tert-butylperoxy)-tetralin by aqueous tert-butylhydroperoxide under phase transfer conditions
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Selective α-peroxidation of tetralin by TBHP is catalyzed by copper salts with the aid of quaternary ammonium compounds in an aqueous-organic biphasic system.
- Feldberg, Liron,Sasson, Yoel
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- Green Organic Solvent-Free Oxidation of Alkylarenes with tert-Butyl Hydroperoxide Catalyzed by Water-Soluble Copper Complex
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Different benzylic compounds were efficiently oxidized to the corresponding ketones with aqueous 70% tert-butyl hydroperoxide (TBHP) and the catalytic system composed of CuCl2.2H2O and 2,2'-biquinoline-4,4'-dicarboxylic acid dipotassium salt (BQC). The catalytic system CuCl2/BQC/TBHP allows obtaining high yields at room temperature under organic solvent-free conditions. The interest of this system lies in its cost effectiveness and its benign nature towards the environment. Benzylic tertbutylperoxy ethers and benzylic alcohols were observed and suggested as the reaction intermediates. Analysis of organic products by atomic absorption did not show any contamination with copper metal. In terms of efficiency, CuCl2/BQC system is comparable or superior to the most of the catalytic systems described in the literature and which are based on toxic organic solvent.
- Ajjou, Abdelaziz Nait,Rahman, Ateeq
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p. 165 - 174
(2020/04/15)
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- Rh2(esp)2-catalyzed allylic and benzylic oxidations
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The dirhodium(ii) catalyst Rh2(esp)2 allows direct solvent-free allylic and benzylic oxidations by T-HYDRO with a remarkably low catalyst loading. This method is operationally simple and scalable at ambient temperature without the use of any additives. The high catalyst stability in these reactions may be attributed to a dirhodium(ii,ii) catalyst resting state, which is less prone to decomposition.
- Wang, Yuanhua,Wang, Yi,Kuang, Yi
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supporting information
p. 5852 - 5855
(2015/03/30)
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- N-heterocyclic carbene dirhodium(II) complexes as catalysts for allylic and benzylic oxidations
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The experimental conditions (solvent, base, temperature and oxidant) for allylic and benzylic oxidation reactions catalyzed by dirhodium(II)/N- heterocyclic carbene (NHC) complexes were optimized for the first time in this work. The oxidations of cyclohexene and fluorene were used as model reactions. Two optimized experimental conditions for both types of oxidations were found, which resulted in their ketone [aerobic conditions, 40 °C, 1 equiv. tBuOOH (TBHP)] or tert-butyl peroxide derivatives (anaerobic conditions, 25 °C, 2 equiv. TBHP). The dirhodium(II) complexes undergo a single-electron reversible oxidation by cyclic voltammetry in CH2Cl2, which is assigned to the Rh24+/Rh25+ redox couple at an oxidation potential that is lowered upon sequential axial coordination of further ligands to the Rh-Rh centre. The oxidation potential is discussed in terms of the electron-donor character of the NHC ligand, which was shown to act as an effective electron-releaser to the Rh2 4+ centre, and the electrochemical behaviour is compared to the observed catalytic activity. An N-heterocyclic carbene (NHC) ligand at the axial position of Rh2(carboxylate)4 complexes triggers considerable changes in the electrochemical behaviour of the formed complexes, which also catalyze allylic and benzylic oxidations. Copyright
- Coelho, Jaime A. S.,Trindade, Alexandre F.,Wanke, Riccardo,Rocha, Bruno G. M.,Veiros, Luis F.,Gois, Pedro M. P.,Pombeiro, Armando J. L.,Afonso, Carlos A. M.
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supporting information
p. 1471 - 1478
(2013/05/09)
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- Synthesis, single crystal structures and efficient catalysis for tetralin oxidation of two novel complexes of Cu(II) with 2-aminomethyl pyridine
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Two novel Cu(II) complexes were synthesized through the reaction of 2-aminomethyl pyridine (AMP) with CuCl2·2H2O by changing the metal/ligand ratio. Their structures were thoroughly characterized by FT-IR, elemental analysis and X-ray diffraction method. The results revealed that complex 1 [Cu(AMP)Cl2] consists of isolated binuclear molecules unit and displays distorted tetragonal pyramid. Complex 2 [Cu(AMP) 2(H2O)2]Cl2 exhibits a octahedral geometry. The complexes were both evaluated as catalysts in the tetralin oxidation with TBHP as oxidant. Complex 1 showed high catalytic activity and selectivity towards α-tetralone under mild conditions. Thus, under the optimized conditions (acetonitrile 10 ml, catalyst 0.045 mmol, tetralin 4.5 mmol, 65% TBHP 22.5 mmol, T = 50 °C), the conversion of tetralin reached 89% with a selectivity of 71% towards α-tetralone. Compared with complex 1, complex 2 displayed low catalytic activity mainly due to the strong steric hindrance from the two coordinated 2-aminomethyl pyridine molecules.
- Wang, Chunling,Zhang, Yuecheng,Yuan, Baoguo,Zhao, Jiquan
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scheme or table
p. 173 - 179
(2011/02/24)
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- Copper-catalyzed homolytic and heterolytic benzylic and allylic oxidation using tert-butyl hydroperoxide
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Allylic and benzylic alcohols were oxidized in good yields to the respective ketones by tert-butyl hydroperoxide (TBHP) in the presence of copper salts under phase-transfer catalysis conditions. This dehydrogenation was found to proceed via a heterolytic mechanism. CuCl2, CuCl, and even copper powder were equally facile as catalysts, as they were all transformed in situ to Cu(OH)Cl which was extracted into the organic phase by the phase-transfer catalyst (PTC). Deuterium labeling experiments evidenced the scission of the benzylic C-H bond in the rate-determining step. Nonproductive TBHP decomposition was not observed in the presence of the alcohol substrates. Conversely, the oxygenation of π-activated methylene groups in the same medium was found to be a free radical process, and the major products were the appropriate tert-butyl peroxides. Catalyst deactivation, solvent effects, and extraction effects are discussed. By applying Minisci's postulations concerning the relative reactivity of TBHP molecules towards tert-butoxyl radicals in protic and nonprotic environments, the coexistence of the homolytic and the heterolytic pathways can be explained. A complete reaction mechanism is proposed, wherein the free-radical oxidation obeys Kochi's mechanism, and the heterolytic dehydrogenation is based on either a high-valent CuIV=O species or a [Cu(OH)Cl]2 species.
- Rothenberg, Gadi,Feldberg, Liron,Wiener, Harold,Sasson, Yoel
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p. 2429 - 2434
(2007/10/03)
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