- Catalytic applications of CuII-containing MOFs based on N-heterocyclic ligand in the oxidative coupling of 2,6-dimethylphenol
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Two CuII complexes bearing a N-heterocyclic ligand, namely [Cu(SO4)(pbbm)]n (1) and {[Cu(Ac)2(pbbm)] · CH3OH}n (2) (pbbm = 1,1′-(1,5-pentanediyl)bis-1H-benzimidazole) have been synthesized with the aim of exploiting new and potent catalysts. Single crystal X-ray diffraction shows that new polymeric complex 1 features 1-D double-chain framework. The catalytic studies on 1 and 2 indicate that they are efficient homogeneous catalysts for the oxidative coupling of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) and diphenoquinone (DPQ) with H2O2 as oxidant and NaOMe as co-catalyst at room temperature. Optimal reaction conditions are obtained by examining the effects of solvent, the reaction time, temperature as well as the amounts of co-catalyst, catalyst and oxidant. Under the optimal conditions, the selectivity to PPE is almost up to 90% for both complexes, and the conversion of DMP is 85% for 1 and 90% for 2, comparable to those observed for highly active catalyst systems in the literature. Further comparison of their catalytic performances with those of the corresponding copper salt together with organic ligand, copper salt alone and free ligand reveals that the coordination of ligand to CuII ion plays a key role in generating the superior reactivities of complexes.
- Xiao, Bo,Hou, Hongwei,Fan, Yaoting
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- Activation of Molecular Oxygen. Mechanistic Studies of the Oxidation of Hindered Phenols with Cobalt-Dioxygen
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Mechanistic studies of the oxidation of various substituted phenols by cobalt(II) bis(3-(salicylideneamino)propyl)methylamine, CoSMDPT, are reported.The reaction is first order in , , and .A series of experiments are reported to provide strong support for a mechanistic scheme that involves reaction of coordinate dioxygen.Coordination of O2 to this cobalt(II) complex enhances the ability of the dioxygen to abstract hydrogen atoms and to react with phenoxy radicals.The mechanism provides a rationale for the influence of several variables on the reaction and suggests steps that were taken to retard catalyst deactivation.
- Zombeck, Alan,Drago, Russell S.,Corden, Barry B.,Gaul, John H.
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- Preparation and Catalytic Oxidizing Potential of Polymer Supported Chelating Amine and Schiff Base Complexes
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A new, versatile, high-yield synthesis for covalently attaching multidentate chelates to polystyrene is described.Polymeric substrates containing bound polydentate amines as discrete units can be obtained by reacting chloromethylated polystyrene with bis(2-cyanoethyl)amine, followed by BH3/THF reduction, to provide polymer-attached bis(3-aminopropyl)amine, (*)-DPT.These materials form the basis for the preparation of a wide variety of chelating ligands, for example, through the Schiff base reaction with various aldehydes and ketones.In order to demonstrate the feasibility of these polymer reactions, the entire sequence of reactions was carried out in solution using benzyl chloride as the starting material.A series of polymer-bound metal complexes were prepared and characterized.ESR spectra of the polymer-bound CuIISalDPT and CoIISalDPT*O2 complexes were very similar to their respective frozen glass spectra.The Moessbauer spectrum of the polymer-bound FeIISalDPT was similar to the powder spectrum.The Fe(II)-bound complex was irreversibly oxidized upon exposure to air.The CoIISalDPT-bound complex was found to be an active catalyst for the oxidation of 2,6-dimethylphenol.A large enhancement in product selectivity is obtained with the polymer Co(II) complex over the solution analogue.
- Drago, Russell S.,Gaul, John,Zombeck, Alan,Straub, Darel K.
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- Synthesis, magnetic behaviour, and X-ray structures of dinuclear copper complexes with multiple bridges. Efficient and selective catalysts for polymerization of 2,6-dimethylphenol
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The use of a potentially tridentate mono-anionic bridging ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)propan-2-ol (bdmpp-H), in assembling new dimeric copper complexes with interesting magnetic properties has been investigated. The reaction of copper hydroxide or copper acetate with phenyl phosphinic acid or diphenyl phosphinic acid in the presence of bdmpp-H produces the dinuclear complexes [Cu(bdmpp)(ppi)]2 (1) and [Cu(bdmpp)(dppi-H)]2(dppi)2 (2) (ppi-H = phenylphosphinic acid; dppi-H = diphenylphosphinic acid), respectively. The products have been characterized with the help of analytical, thermal, and spectroscopic (IR, UV-vis, and EPR) techniques. Single crystal X-ray diffraction studies of 1 and 2 reveal that the two bdmpp ligands hold together the dimeric copper unit in each complex through -O alkoxide and the pyrazolyl nitrogen ligating centers. Two phenyl phosphinate ligands additionally bridge the dicopper core in 1 to result in octahedral coordination geometry around each metal ion. The diphenyl phosphinic acid acts as a terminal ligand in 2, and thus completes a square pyramidal geometry around each copper ion. Both complexes show a very short Cu...Cu separation (3.001 and 3.065 A for 1 and 2, respectively). The investigation of the magnetic properties reveals the efficiency of the double alkoxide bridge between the two paramagnetic copper ions to mediate strong antiferromagnetic interactions [J/kB = -620(5) K (-431(4) cm -1) and -685(5) K (-476(4) cm-1) for 1 and 2, respectively]. Compounds 1 and 2, along with a few other copper phosphate complexes, were tested as catalysts for the oxidative polymerization of 2,6-dimethylphenol; 1 and 2 were found to be efficient catalysts with an increased selectivity for the formation of the polyphenylene ether. However a related mononuclear octahedral copper complex [Cu(imz)4(dtbp) 2] (dtbp-H = di-tert-butylphosphate) was found to be more efficient. The Royal Society of Chemistry.
- Murugavel, Ramaswamy,Pothiraja, Ramasamy,Gogoi, Nayanmoni,Clerac, Rodolphe,Lecren, Lollita,Butcher, Ray J.,Nethaji, Munirathinam
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- Studies in peroxidase action-XVII. Some general observations
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The peroxidase system oxidizes, 2,6-dimethylphenol and 2,6-dimethoxyphenol smoothly to the corresponding tetrasubstituted diphenoquinones; by contrast 2,6-dichlorophenol and 2,4,6-trichlorophenol given intractable products believed to result from the hydr
- Saunders,Stark
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- Hydrothermal syntheses of metal-organic frameworks constructed from aromatic polycarboxylate and 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl
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Six new metal-organic frameworks, namely, {[Co(btmb)(HBTC)]?2H 2O}n (1), {[Co3(btmb)3(BTC) 2(H2O)2]?6H2O}n (2), {[Co3(btmb)3(BTC)2(H2O) 4]?2H2O}n (3), {[Ni3(btmb) 3(BTC)2(H2O)4]?2H 2O}n (4), [Cu(btmb)(HBTC)]n (5), and [Cu(btmb)(NDC)]n (6) (H3BTC = 1,3,5-benzenetricarboxylic acid, H2NDC = 1,2-benzenedicarboxylic acid, and btmb = 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl), have been synthesized under hydrothermal conditions. The structure of 1 is a 6-connected self-penetrating three-dimensional (3D) framework with 44?610?8 topology. Complex 2 exhibits a trinodal (3,4)-connected topology with a Schlaefli symbol of (62?84)(64? 82)(63). Both complexes 3 and 4 possess 3D pillar-layered structures with a Schlaefli symbol of (62?8?10 3)(64?8?10)(6?102). Complex 5 is also a 3D polymer with a pillar-layered framework, which can be simplified as the (63)(69?8) topology. Complex 6 shows a 4-connected 3D framework with a Schlaefli notation of (65?8) 2. Furthermore, complexes 1-6 as heterogeneous catalysts were studied in the green catalysis process of the oxidative coupling of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) and diphenoquinone (DPQ). The results show that these complexes exhibit different catalytic activities; both the Cu complexes are catalytically active by showing high conversion of DMP and high selectivity of PPE, and they exhibit great potential as recyclable catalysts.
- Mu, Yajuan,Fu, Junhong,Song, Yajing,Li, Zhen,Hou, Hongwei,Fan, Yaoting
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- Syntheses, crystal structures of a series of copper(II) complexes and their catalytic activities in the green oxidative coupling of 2,6-dimethylphenol
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Three mixed-ligand CuII complexes bearing iminodiacetato (ida) and N-heterocyclic ligands, namely, [Cu2(ida)2(bbbm)(H2O)2] · H2O (1), [Cu2(ida)2(btx)(H2O)2] · 2H2O (2) and [Cu2(ida)2(pbbm)(H2O)2] · H2O · 3CH3OH (3) (bbbm = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole, btx = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, pbbm = 1,1′-(1,3-propanediyl)bis-1H-benzimidazole), in addition to three fcz-based CuII complexes, namely, {[Cu(fcz)2(H2O)2] · 2NO3}n (4), {[Cu(fcz)2(H2O)] · SO4 · DMF · 2CH3OH · 2H2O}n (5) and {[Cu(fcz)2Cl2] · 2CH3OH}n (6) (fcz = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-l-yl) methyl]ethanol) have been prepared according to appropriate synthetic strategies with the aim of exploiting new and potent catalysts. Single crystal X-ray diffraction shows that 1 and 2 possess similar binuclear structures, 3 features a 2D pleated network, and 4 exhibits a 1D polymeric double-chain structure. Complexes 1-6 are tested as catalysts in the green catalysis process of the oxidative coupling of 2,6-dimethylphenol (DMP). Under the optimized reaction conditions, these complexes are catalytically active by showing high conversion of DMP and high selectivity of PPE. The preliminary study of the catalytic-structural correlations suggests that the coordination environment of the copper center have important influences on their catalytic activities.
- Zhang, Erpeng,Hou, Hongwei,Han, Huayun,Fan, Yaoting
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- Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions
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Depolymerization of an engineering plastic, poly(2,6-dimethyl-1, 4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (Mn = 1.0 × 104, M w/Mn = 1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to Mn = 4.9 × 102 (Mw/Mn = 1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.
- Saito, Kei,Masuyama, Toru,Oyaizu, Kenichi,Nishide, Hiroyuki
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- Laccase initiated C-C couplings: Various techniques for reaction monitoring
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In this study the fungal laccase from Myceliophthora thermophila (Novozym 51003) was investigated for oxidative C-C couplings of phenolic compounds. This enzyme requires only molecular oxygen as oxidant, which represents a great advantage for oxidative coupling reactions. However, such couplings are typically considered as highly unselective, due to the radical reaction mechanism of laccases. Based on different analytical techniques we gained detailed insights into laccase initiated coupling reactions. A preselection of potential substrates was realized via oxygen measurement during laccase initiated oxidations. Furthermore in situ FT-IR spectroscopy facilitated analyses in-depth, due to feasibility to detect dissolved as well as solid compounds. This technique allowed the detection of the grade of couplings of various laccase substrates, depending on different conditions. As a result oxidative dimerizations of 2,6-disubstituted phenols could be identified as highly selective and were scaled-up to multigram scale. Thereby the oxidation product of 2,6-diisopropyl phenol can be easily reduced to the corresponding biphenol, the antibacterial agent dipropofol. The presented techniques open up new biocatalytical approaches receiving quinoid units as key elements of many natural compounds and pharmaceuticals.
- Engelmann, Claudia,Illner, Sabine,Kragl, Udo
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- Carboxylic-supported copper complexes as catalyst for the green oxidative coupling of 2,6-dimethylphenol: Synthesis, characterization and structure
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Three new Cu(II) complexes with carboxylic ligand, namely {[Cu(qc) 2(py)]·4H2O}∞ (1), [Cu(qc) 2(4,4′-bpy)]∞ (2) and [Cu(pc)(2,2′-bpy) (H2O)]2·H2O (3) (Hqc = 3-hydroxy-2-quinoxalinecarboxylic acid, H2pc = 4-hydroxyphthalic acid, py = pyrazine) have been synthesized and characterized. In both 1 and 2, each Cu(II) ion is coordinated by two quinoxalinecarboxylate moieties in the equatorial plane and two 4,4′-bpy or pyrazine units provide coordination in the axial positions, thus, resulting in a 1-D polymeric chain structure. Complex 3 has a dimeric structure in which two Cu(II) cations are bridged by two deprotonated pc2- ligands and two 2,2′-bpy molecules. As heterogeneous catalysts, the title complexes showed high catalytic efficiency in the green oxidative polymerization of 2,6-dimethylphenol (DMP) to poly(1,4-phenylene ether) (PPE) in the presence of H2O2 as oxidant in water under mild conditions. Moreover, they allow reuse without significant loss of activity through four runs, which suggests that these catalysts are efficient, mild, and easily recyclable for the oxidative coupling of DMP. The preliminary study of the catalytic-structural correlations suggests that the coordination environment of the metal center plays an important role in the improvement of their catalytic efficiencies.
- Liu, Qi,Wu, Huai Guang
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- Transformation of Formazanate at Nickel(II) Centers to Give a Singly Reduced Nickel Complex with Azoiminate Radical Ligands and Its Reactivity toward Dioxygen
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The heteroleptic (formazanato)nickel bromide complex LNi(μ-Br)2NiL [LH = Mes-NH-N═C(p-tol)-N═N-Mes] has been prepared by deprotonation of LH with NaH followed by reaction with NiBr2(dme). Treatment of this complex with KC8led to transformation of the formazanate into azoiminate ligands via N-N bond cleavage and the simultaneous release of aniline. At the same time, the potentially resulting intermediate complex L′2Ni [L′ = HN═C(p-tol)-N═N-Mes] was reduced by one additional electron, which is delocalized across the π system and the metal center. The resulting reduced complex [L′2Ni]K(18-c-6) has aS=1/2ground state and a square-planar structure. It reacts with dioxygen via one-electron oxidation to give the complex L′2Ni, and the formation of superoxide was detected spectroscopically. If oxidizable substrates are present during this process, these are oxygenated/oxidized. Triphenylphosphine is converted to phosphine oxide, and hydrogen atoms are abstracted from TEMPO-H and phenols. In the case of cyclohexene, autoxidations are triggered, leading to the typical radical-chain-derived products of cyclohexene.
- Ar, Deniz,Kilpatrick, Alexander F. R.,Cula, Beatrice,Herwig, Christian,Limberg, Christian
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supporting information
p. 13844 - 13853
(2021/05/04)
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- Method for synthesizing and preparing 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone
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The invention relates to a method for synthesizing and preparing 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone. According to the method, a novel bis(2-hydroxyloxo-1,10-o-phenanthroline minus monovalent anion)binuclear cuprous (I) complex is added into a synthesis reaction system, and the 3,3',5,5'-tetraalkyl-4,4'-biphenyl quinone is synthesized and prepared from 2,6-dialkyl phenol in a high-selectivity manner under the conditions that a temperature is relatively low, the reaction time is relatively short, a reaction solvent is economical and air serves as an oxidant.
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Paragraph 0050-0051; 0061-0063; 0072
(2020/02/27)
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- Method for synthesizing high-purity 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone through Cu-BTC catalysis
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The invention discloses a method for synthesizing high-purity 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone through Cu-BTC catalysis. According to the method, trimesic acid and copper nitrate hydrateare hydrothermally synthesized into a Cu-BTC catalyst; under the alkaline emulsion reaction condition, hydrogen peroxide is utilized as an oxidizing agent, and 2,6-xylenol is oxidized and coupled intothe high-purity 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone; product quality yield of the high-purity 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone is 90 to 95%, and a product purity mass percent of the high-purity 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone is 98%; reaction temperature is 70 to 85 DEG C, and reaction time is 4 to 8h; the catalyst is easy to separate and recycle; after beingrepeatedly used for four times, quality yield of the 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone still reaches 87.5%, and purity of the 3,3',5,5'-tetramethyl-4,4'-biphenyl diquinone is 97.8%; alkaliemulsified filtrate and washing liquor can be recycled and deployed to be used repeatedly; a reaction condition is moderate, and a synthesizing technology has the advantages of greenness and environmental friendliness.
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Paragraph 0018-0043
(2018/04/01)
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- Selective, Catalytic, and Metal-Free Coupling of Electron-Rich Phenols and Anilides Using Molecular Oxygen as Terminal Oxidant
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Selective oxidative homo- and cross-coupling of electron-rich phenols and anilides was developed using nitrosonium tetrafluoroborate as a catalyst. Oxidative coupling of phenols revealed unusual selectivities, which translated into the unprecedented synthesis of inverse Pummerer-type ketones. Mechanistic studies suggest that oxidative coupling of phenols and anilides shares a common pathway via homolytical heteroatom-hydrogen bond cleavage. Nitrosonium salt catalysis was applied for cross-dehydrogenative coupling initiated by generation of heteroatom-centered radicals.
- Bering, Luis,Vogt, Melina,Paulussen, Felix M.,Antonchick, Andrey P.
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supporting information
p. 4077 - 4080
(2018/07/15)
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- Synthesis method of 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone
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The invention provides a synthesis method of 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone. 2,6-dialkyl phenol is dissolved in a reaction solvent; a copper ion loaded hydrophobic modified resin catalyst and an oxidizing agent are added; reaction is performed for 2 to 8h at 40 DEG C to 80 DEG C; filtering is performed to obtain filter liquid; then, the filter liquid is distilled; distillation residues are cleaned by alkanol; after the drying, the 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone is obtained. The synthesis method is simple; after being recovered, the catalyst can be repeatedly used; the reaction selectivity is high; the yield of the 3,3',5,5'-tetraalkyl-4,4'-diphenoquinone can reach 95 percent or higher; no by-product of polyphenyl ether is generated; the copper ion content is smaller than 5mu g/g; the product purity is greater than or equal to 99.5 percent.
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Paragraph 0058; 0059; 0060; 0061; 0062; 0063-0074
(2017/08/29)
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- Solvent-controlled selective synthesis of biphenols and quinones: Via oxidative coupling of phenols
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A regioselective synthesis of unsymmetrical and symmetrical biphenols and binaphthols via oxidative coupling of phenols or naphthols in the presence of K2S2O8 in CF3COOH under ambient conditions is described. Interestingly, the 1:1 ratio of H2O and CH3CN solvent mixtures at 80 °C instead of CF3COOH provided substituted unsymmetrical quinones. A gram-scale synthesis of biphenols and binaphthols was demonstrated.
- More, Nagnath Yadav,Jeganmohan, Masilamani
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supporting information
p. 9616 - 9619
(2017/09/01)
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- A dual-functional heterogeneous ruthenium catalyst for the green one-pot synthesis of biphenols
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A green one-pot synthesis of biphenols using O2 and H2 was achieved using a magadiite-supported Ru nanoparticle catalyst. This catalyst selectively promoted the oxidative coupling of phenols to diphenoquinones with O2, followed by the successive reduction of these diphenoquinones to biphenols using H2 in a single reactor.
- Maeno, Zen,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro
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p. 3205 - 3209
(2017/08/16)
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- Selective c-c coupling reaction of dimethylphenol to tetramethyldiphenoquinone using molecular oxygen catalyzed by cu complexes immobilized in nanospaces of structurally-ordered materials
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Two high-performance Cu catalysts were successfully developed by immobilization of Cu ions in the nanospaces of poly(propylene imine) (PPI) dendrimer and magadiite for the selective C-C coupling of 2,6-dimethylphenol (DMP) to 3,3′,5,5′-tetramethyldiphenoquinone (DPQ) with O2 as a green oxidant. The PPI dendrimer encapsulated Cu ions in the internal nanovoids to form adjacent Cu species, which exhibited significantly high catalytic activity for the regioselective coupling reaction of DMP compared to previously reported enzyme and metal complex catalysts. The magadiite-immobilized Cu complex acted as a selective heterogeneous catalyst for the oxidative C-C coupling of DMP to DPQ. This heterogeneous catalyst was recoverable from the reaction mixture by simple filtration, reusable without loss of efficiency, and applicable to a continuous flow reactor system. Detailed characterization using ultraviolet-visible (UV-vis), Fourier transform infrared (FTIR), electronic spin resonance (ESR), and X-ray absorption fine structure (XAFS) spectroscopies and the reaction mechanism investigation revealed that the high catalytic performances of these Cu catalysts were ascribed to the adjacent Cu species generated within the nanospaces of the PPI dendrimer and magadiite.
- Maeno, Zen,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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p. 3089 - 3106
(2015/09/02)
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- Improved Protocol for Mononitration of Phenols with Bismuth(III) and Iron(III) Nitrates
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A simple and efficient multigram procedure was developed for the selective mononitration of various activated phenols. The reaction proceeded smoothly with 0.5 equivalents of Bi(NO3)3 · 5H2O or Fe(NO3)3 · 9H2O in acetone at ambient temperature or at reflux. The desired products were isolated in 62-93% total yield and essentially no overnitrated compounds were detected.
- W?sińska, Ma?gorzata,Korczewska, Anna,Giurg, Miros?aw,Skarzewski, Jacek
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supporting information
p. 143 - 150
(2015/10/20)
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- {Cu2+-Co3+-Cu2+} and {Cu 2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co 3+-Cu+} (3), {Cu+-Fe3+-Cu +} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu 2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu +} (3), {Cu+-Fe3+-Cu+} (4), {Cu 2+-Co3+-Cu2+} (5), and {Cu2+-Fe 3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes. Copyright
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2014/05/06)
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- A green mesostructured vanadosilicate catalyst and its unprecedented catalytic activity for the selective synthesis of 2,6-disubstituted p-benzoquinones
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We have developed a green method for the production of 2,6-disubstituted p-benzoquinones (DSBQs) by liquid-phase oxidations of di/tri-substituted phenols using two-dimensional hexagonally thick-walled mesoporous vanadosilicate catalysts. In particular, 2,6-di-tert-butyl-p-benzoquinone was synthesized by the oxidation of 2,6-di-tert-butylphenol, using various reaction parameters, over mesoporous VSBA-15 catalysts synthesized with various vanadium contents. A promising chemical treatment method for the preparation of green mesoporous VSBA-15(5) or W-VSBA-15(5) (W: washed) catalysts was successfully used in the presence of ammonium acetate solution to remove moderately toxic non-framework V2O5 crystallite species from the active surface, and the catalytic activity of the recovered green mesoporous VSBA-15(5) catalyst was determined. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. The combined results show that the green mesoporous VSBA-15(5) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of DSBQs (98-100%), and has unprecedented catalytic activity compared with other mesoporous vanadosilicate catalysts. The Royal Society of Chemistry 2014.
- Selvaraj,Park,Kim
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p. 958 - 966
(2014/01/06)
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- Regioselective oxidative coupling of 2,6-dimethylphenol to tetramethyldiphenoquinone using polyamine dendrimer-encapsulated Cu catalysts
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The polyamine dendrimer-encapsulated Cu complexes are capable of regioselectively catalyzing the oxidative coupling reaction of 2,6-dimethylphenol to tetramethyldiphenoquinone in high yield. The polyamine dendrimer nanovoids encapsulate Cu ions in such a manner that adjacent Cu centers are able to serve as active species for the reaction.
- Maeno, Zen,Okao, Motohiro,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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p. 9662 - 9665
(2013/09/02)
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- An antimony(V) substituted Keggin heteropolyacid, H4PSbMo 11O40: Why is its catalytic activity in oxidation reactions so different from that of H4PVMo11O 40?
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An antimony(V) containing α-Keggin type acidic polyoxometalate, H4PSbMo11O40, was prepared by reacting NaMoO4, H3PO4 and Sb2O3 in the presence of aqua regia to appraise its reactivity compared to the well known vanadate analog, H4PVMo11O40. Characterization was by X-ray diffraction, MALDI-TOF MS, IR, UV-vis and 31P NMR spectroscopy. Catalytic redox reactions, such as oxidative dehydrogenation using O2 and N2O as terminal oxidants were studied and showed very different reactivity of H4PSbMo 11O40 versus H4PVMo11O40. It was found by DFT calculations that in contrast to analogous H 4PVMo11O40 where vanadium centered catalysis is observed, in H4PSbMo11O40 catalysis is molybdenum and not antimony centered.
- Goldberg, Hila,Kumar, Devesh,Sastry, G. Narahari,Leitus, Gregory,Neumann, Ronny
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experimental part
p. 152 - 157
(2012/04/17)
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- Efficient oxidative coupling of 2,6-disubstituted phenol catalyzed by a dicopper(II) complex
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Complexation of a rigid multi-pyridine ligand bis(2-pyridyl)-1,8- naphthyridine (bpnp) with [Cu2(TFA)4] (TFA = trifluoroacetate) resulted in the formation of a dinuclear copper(ii) complex, namely [Cu2(bpnp)(μ-OH)(TFA)3] (1). This complex has been characterized by X-ray crystallographic, spectroscopic and elemental analyses. Complex 1 is an efficient catalyst for the oxidative coupling of various 2,6-disubstituted phenols with molecular oxygen. Yields and selectivity depend on the reaction conditions employed, the best results being obtained in isopropanol or dioxane at 90 °C with yields of >99%. Mechanistic pathway of the catalysis is discussed.
- Liao, Bei-Sih,Liu, Yi-Hung,Peng, Shei-Ming,Liu, Shiuh-Tzung
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scheme or table
p. 1158 - 1164
(2012/03/07)
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- PHOSPHORUS-CONTAINING COMPOUND AND METHOD FOR PREPARING THE SAME
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The present invention provides a phosphorus-containing compound of formula (I): wherein R1, R2, R3 and R4 are the same or different; and R1, R2, R3 and R4 are independently selected from the group consisting of hydrogen, halogen, C1-8 alkyl, haloalkyl, and alkoxy. The phosphorus-containing compound is prepared by bonding a bisphenol group to a phosphorus atom to prevent the phosphorus-containing heterocyclic molecule from exhibiting steric hindrance on hydroxyl functional groups, thereby increasing reactivity in the subsequent reactions.
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Page/Page column 3
(2010/05/13)
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- Carbonic anhydrase inhibitors. Inhibition of human erythrocyte isozymes I and II with a series of antioxidant phenols
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The inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II, with a series of phenol derivatives was investigated by using the esterase assay, with 4-nitrophenyl acetate as substrate. 2,6-Dimethylphenol, 2,6-diisopropylphenol (propofol), 2,6-di-t-butylphenol, butylated hydroxytoluene, butylated hydroxyanisole, vanillin, guaiacol, di(2,6-dimethylphenol), di(2,6-diisopropylphenol), di(2,6-di-t-butylphenol), and acetazolamide showed KI values in the range of 37.5-274.5 μM for hCA I and of 0.29-113.5 μM against hCA II, respectively. All these phenols were non-competitive inhibitors with 4-nitrophenylacetate as substrate. Some antioxidant phenol derivatives investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms which have not been yet assayed for their interactions with such agents.
- Sentuerk, Murat,Guelcin, Ilhami,Dastan, Arif,Irfan Kuefrevioglu, Oe.,Supuran, Claudiu T.
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experimental part
p. 3207 - 3211
(2009/09/08)
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- Enantioselective synthesis of bicyclo[2.2.2]octenones using a copper-mediated oxidative dearomatization/[4 + 2] dimerization cascade
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An enantioselective approach to bicyclo[2.2.2]octenone structures utilizing a copper-mediated asymmetric oxidative dearomatization/[4 + 2] dimerization cascade is described. The total synthesis and absolute stereochemistry reassignment of (+)-aquaticol has been achieved using the methodology. Copyright
- Dong, Suwei,Zhu, Jianglong,Porco Jr., John A.
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p. 2738 - 2739
(2008/09/19)
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- Heterogeneously catalyzed aerobic oxidative biaryl coupling of 2-naphthols and substituted phenols in water
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The oxidative coupling reaction can efficiently be promoted by supported ruthenium catalyst Ru(OH)x/Al2O3. A variety of 2-naphthols and substituted phenols can be converted to the corresponding biaryl compounds in moderate to excellent yields using molecular oxygen as a sole oxidant in water without any additives. The catalysis is truly heterogeneous in nature, and Ru(OH)x/Al2O3 can easily be recovered after the reaction. The catalyst can be recycled seven times with the maintenance of the catalytic performance, and the total turnover number reaches up to 160. The results of competitive coupling reactions suggest that the present oxidative biaryl coupling reaction proceeds via the homolytic coupling of two radical species and the Ru(OH)x/Al2O3 catalyst acts as an one-electron oxidant. Two radical species are coupled to give the corresponding biaryl product, and the one-electron reduced catalyst is reoxidized by molecular oxygen. The amounts of O2 uptake and H 2O formation were almost one-quarter and one-half the amount of substrate consumed, respectively, supporting the reaction mechanism. The kinetic data and kinetic isotope effect show that the reoxidation of the reduced catalyst is the rate-limiting step for the coupling reaction.
- Matsushita, Mitsunori,Kamata, Keigo,Yamaguchi, Kazuya,Mizuno, Noritaka
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p. 6632 - 6640
(2007/10/03)
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- Selective oxidative para C-C dimerization of 2,6-dimethylphenol
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Mechanistic investigations on the oxidative coupling of 2,6-dimethylphenol have led to the development of a selective and efficient procedure to prepare 3,5,3′,5′-tetramethyl-biphenyl-4,4′-diol, via a C-C coupling, mediated by a hypervalent form of iodine, i.e. (diacetoxyiodo)benzene and for which a mechanism is proposed. The Royal Society of Chemistry 2005.
- Boldron, Christophe,Aromi, Guillem,Challa, Ger,Gamez, Patrick,Reedijk, Jan
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p. 5808 - 5810
(2008/02/02)
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- Oxidative Polymerization of 2,6-Dimethylphenol to Form Poly(2,6-dimethyl-1,4-phenyleneoxide) in Water
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Green polymerization: The simple stirring of 2,6-dimethylphenol with an excess of oxidant or a catalytic amount of a copper complex in an alkaline aqueous solution yields poly (2,6-dimethyl-1,4-phenyleneoxide), a commercially important polymer (see scheme). The formed polymer was easily separated as an off-white powder by filtration.
- Saito, Kei,Tago, Takahiro,Masuyama, Toru,Nishide, Hiroyuki
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p. 730 - 733
(2007/10/03)
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- A convenient synthesis of nickel(II) and cobalt(II) complexes of unsymmetrical salen-type ligands and their application as catalysts for the oxidation of 2,6-dimethylphenol and 1,5-dihydroxynaphthalene by molecular oxygen
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Salen-type ligands 1-4 have been synthesized in high yields, from which the nickel(II) complexes 9-11 and the cobalt(II) complexes 12 and 13 have been prepared and characterized. The complexes have been assessed for their ability to activate molecular oxygen in the catalytic oxidation of phenols, namely, 2,6-dimethylphenol and 1,5-dihydroxynaphthalene. The nickel complexes 9-11 are inactive in the oxidation of the phenols but the cobalt complexes 12 and 13 show high catalytic activity.
- Adam, Waldemar,Saha-Moeller, Chantu R.,Ganeshpure, Pralhad A.
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- PREPARATION OF BIPHENOLS BY OXIDATIVE COUPLING OF ALKYLPHENOLS USING A RECYCLABLE COPPER CATALYST
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A method for producing biphenols by oxidative coupling of dialkylphenols which proceeds in two stages is disclosed, using a copper-amine complex which is catalytically active in each stage. A novel copper-amine complex is also disclosed which exhibits high catalytic activity for the oxidative coupling of substituted phenols under mild conditions, has dual (two stage) activity, and can be readily recycled and reused.
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- Catalytic oxidation of hindered phenols by a copper(I) complex and dioxygen
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The dioxygen reaction product of a binuclear copper(I) complex of a new m-xylyl-based ligand has proven to be a catalyst in the promotion of oxidative carbon-carbon coupling of hindered phenols, which leads to bisphenol and diphenoquinones. (C) 2000 Elsevier Science Ltd.
- Gupta,Mukherjee
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p. 7763 - 7767
(2007/10/03)
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- (Nitrosonaphtholato)metal complex-catalyzed oxidation of phenols and alkenes
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Bis(1-nitroso-2-naphtholato)manganese(II), tris(1-nitroso-2-naphtholato)manganese(III), tris(2-nitroso-1-naphtholato)manganese(III), bis(1-nitroso-2-naphtholato)cobalt(II), bis(1-nitroso-2-naphtholato)nickel(II), bis(1-nitroso-2-naphtholato)copper(II) and bis(1-nitroso-2-naphtholato)zinc(II) were prepared and their catalytic abilities in the oxidation of phenols were examined. The best yields of diphenoquinones were obtained when the catalytic oxidation using bis(1-nitroso-2-naphtholato)manganese(II) was carried out at 23°C under an oxygen atmosphere (1 atm) in the presence of a phosphine ligand. Likewise, phenols were completely converted to the corresponding diphenoquinones together with small amounts of benzoquinones under an oxygen pressure (20 atm) at 50°C in a short period of time. It was proven that the manganese(II) catalyst, molecular oxygen, and phosphine ligand were essential for the catalytic phenol oxidation. On the other hand. bis(1-nitroso-2-naphtholato)manganese(II)-catalyzed epoxidation of alkenes was only effective when iodosylbenzene was used. The catalytic oxidation mechanism was discussed on the basis of the measurement of cyclic voltammograms of the (nitrosonaphtholato)metal complexes, isolated intermediates, and effect of additives.
- Nishino, Hiroshi,Satoh, Hideaki,Yamashita, Mayumi,Kurosawa, Kazu
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p. 1919 - 1924
(2007/10/03)
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- Efficient oxidation of various phenols catalyzed by Di-μ-hydroxodicopper(II) complexes of a hexapyridine dinucleating ligand
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The di-μ-hydroxodicopper(II) complexes [Cu2(OH)2-(hexpy)](X)2 [X = ClO4 and CF3SO3, hexpy: 1,2-bis[2-di-(2-pyridyl)methyl-6-pyridyl]ethane] efficiently catalyze the oxidation of various phenols with H2O2.
- Kodera, Masahito,Shimakoshi, Hisashi,Tachi, Yoshimitsu,Katayama, Kou,Kano, Koji
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p. 441 - 442
(2007/10/03)
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- Electron Transfer and Contact Ion Pair Formation, 42. Cyclovoltammetric and ESR/ENDOR Investigations of the One-Electron Reduction of Diphenoquinones
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Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations.In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li(+) and Na(+), while K(+) forms no ion pair.The 3,3',5,5'-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me(+), although Rb(+) and Cs(+) seem to be present solvent-separated in solution.The tetramethyl-substituted radical anion unfortunately polymerizes rapidly.Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation (.+), or the difference in the coupling constants upon Me(+) docking at one δ(-)O=C group, suggesting that about 87percent of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion.Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural charecterization should be attempted. - Keywords: One-Electron Reduction of Diphenoquinones; Cyclovoltammetry; ESR/ENDOR Spectra; Contact Ion Pairs and Triples
- John, Andreas,Bock, Hans
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p. 1699 - 1716
(2007/10/03)
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- Redox Interactions of Cr(VI) and Substituted Phenols: Products and Mechanism
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The mechanisms of aqueous oxidation-reduction interactions between Cr(VI) and substituted phenols (RArOH) were characterized by kinetic analysis and determinations of reaction products and intermediates. A rapid, peroxidative equilibrium between HCrO4(-) and RArOH forms chromate ester intermediates, as verified by spectroscopy. The subsequent rate-limiting ester decomposition proceeds via innersphere electron transfer. The overall rate dependence on [H(+)] is well accounted for by three parallel redox pathways involving zero, one, and two protons. The two-proton pathway dominates at pH = 5. The parallel reaction rate expression was fitted to data for 4-methyl-, 4-methoxy-, 2,6-dimethoxy-, and 3,4-dimethoxyphenol for pH 1-6. Beside accurately predicting rates for the calibrated conditions, the model predicts a sharp decline in rates at pH >= 6. Rates subsequently measured at pH 7 agreed well with those calculated a priori. Such predictions suggest that the proposed mechanism is robust and accurate. Rate constants were correlated with Hammett-type substituent parameters. Reaction products indicated both one- and two-electron pathways.
- Elovitz, Michael S.,Fish, William
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p. 1933 - 1943
(2007/10/03)
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- Oxidation of some Disubstituted Anisole Derivatives with Ceric Perchlorate in Perchloric Acid Solution
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The influence of concentration of particular reagents on the kinetics of Ce(IV) reduction by 2,6-dimethyl and 3,5-dimethyl-anisole as well as 2-methoxy-5-methyl- and 4-methoxy-2-methyl-aniline in perchloric acid solution was investigated, establishing the stoichiometry of these processes.Some intermediate products - macromolecular, derivatives of p-benzoquinone and 4,4'-diphenoquinone - were separated and identified.The effects of substituents and the conditions of performed oxidation processes on the kind and yield of the resultant products were considered.Key words: oxidation, anisole derivatives, kinetics
- Leszczynski, L.,Dziegiec, J.
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p. 1855 - 1862
(2007/10/02)
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- Oxidation of Phenols and Hydroquinones by Dioxygen Catalyzed by Mixed Addenda Heteropolyoxometalate on Active Carbon (NPV6Mo6/C)
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Vanadomolybdophosphate supported on active carbon, NPV6Mo6/C, catalyzed the oxidation and coupling reaction of 2,3,6-trimethylphenol by dioxygen to give trimethyl-p-benzoquinone and 4,4'-dihydroxy-2,2',3,3',5,5'-hexamethylbiphenyl, respectively, depending on the solvent used.Hydroquinones and benzyl alcohol were selectively dehydrogenated by the present system, giving the corresponding p-benzoquinones and benzaldehyde, respectively, in good yields.
- Fujibayashi, Shinya,Nakayama, Kouichi,Nishiyama, Yutaka,Ishii, Yasutaka
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p. 1345 - 1348
(2007/10/02)
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- Oxidation of activated phenols by dioxygen catalysed by the H5PV2Mo10O40 heteropolyanion
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The H5PV2Mo10O40 heteropolyanion has been found to catalyse the highly selective aerobic oxidation of dialkylphenols to diphenoquinones and the oxidation of 2,3,5-trimethylphenol to the 2,3,5-trimethyl-1,4-benzoquinone. The rate is highly dependent on the oxidation potential of the substrate and is proceeds by electron transfer from the phenol substrate to the heteropolyanion catalyst.
- Lissel,Jansen In De Wal,Neumann
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p. 1795 - 1798
(2007/10/02)
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- Choice of Manganese(III) Complexes for the Synthesis of 4,4'-Biphenyldiols and 4,4'-Diphenoquinones
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2,6-Disubstituted phenols are oxidized with tris(2,4-pentanedionato)manganese(III), , in glacial acetic acid to give the corresponding 4,4'-biphenyldiols in high yields, whereas similar reactions using manganase(III) acetate, , instead of quantitatively yield the corresponding 4,4'-diphenoquinones.Cross-coupling reactions of 2,6-di-t-butylphenol and other substituted phenols afford the corresponding cross-coupled 4,4'-biphenyldiols and 4,4'-diphenoquinones together with oxidation products derived from them starting phenols themselves.The advantageous use of and Mn(OAc)3> in the ubiqitous phenol coupling reaction is discussed.
- Nishino, Hiroshi,Nobuyuki, Itoh,Nagashima, Makiko,Kurosawa, Kazu
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p. 620 - 622
(2007/10/02)
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- Reaction of 2,6-Disubstituted Phenols with Vinyllead Triacetates and Alk-1-ynyllead Triacetates: Synthesis of 6-Vinyl- and 6-Alkynyl-Cyclohexa-2,4-dienones and Crystal Structure of 1,3,5,7-Tetramethyl-3,5-bis(phenylethynyl)-1,3,4,4a,5,8a-hexahydro-1,4-ethenonaphthalene-2,6-dione
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(E)-Styryllead triacetate 9, generated by reaction of lead tetraacetate with trimethylstannane 7, has been found to react with 2,4,6-trimethylphenol 1 to give the 6-(E)-styrylcyclohexa-2,4-dienone 11 in high yield.This electrophilic vinylation reaction has been investigated for the vinyllead triacetates 9 and 10 and the 2,6-dimethylphenols 1, 13, 14 and 15.An analogous alkynylation reaction occurred when phenylethynyllead triacetate 24 was treated with 2,4,6-trimethylphenol; however, the product in this case, cyclohexadienone 25, underwent a Diels-Alder dimerisation to give the 1,4-ethenonaphthalene 26.The product 28 from a reaction of the phenylacetylenelead compound 24 and 2,6-dimethylphenol behaved similarly, and here the 1,4-ethenonaphthalene structure 27 for the dimer was determined by single crystal X-ray analysis.
- Hambley, Trevor W.,Holmes, Rodney J.,Parkinson, Christopher J.,Pinhey, John T.
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p. 1917 - 1922
(2007/10/02)
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- Oxidation by Cobalt(III) Acetate. Part 13. Oxidation of Substituted Phenols with Cobalt(III) Acetate in Acetic Acid
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The oxidation of 2,6-di- and 2,4,6-tri-substituted phenols with cobalt(III) acetate has been investigated in acetic acid under an inert atmosphere; the former gave the corresponding diphenoquinones in excellent yields, and the latter yielded side-chain or nuclear acetoxylated products in moderate to good yields.
- Hirano, Masao,Ishii, Tadamichi,Morimoto, Takashi
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p. 1434 - 1436
(2007/10/02)
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- Dioxygen uptake and catalytic activity of some monomeric copper(II) compounds containing an N,S donor ligand. The X-ray structure of bisbis(tetrafluoroborato)copper(II)
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The synthesis and characterization of the copper tetrafluoroborate compound containing the bidentate N,S ligand 5-methyl-4-(ethylthiomethyl)imidazole (memi), , is described.The activities of this compound and of (NO3)2 as oxidation catalysts have been determined in the reaction of 2,6-dimethylphenol with molecular dioxygen to give polyphenylene oxide (PPO) and diphenoquinone (DPQ).For optimum catalysis, an additional base is required in order to dehydrogenate the phenol.Triethylamine proved to be most useful as a base.Initial reaction rates encountered are between 1E-5 and 6E-5 M O2/s and ca. 50percent of thephenol was converted after a reaction time of one hour.Less than 10percent phenol was converted into DPQ.Both compounds have comparable reactivities.A single crystal of was used in an X-ray structure determination: monoclinic space group C2/c, a=13.844(4) Angstroem, b= 11.251(1) Angstroem, c= 15.753(4) Angstroem, β= 111.39(2) deg, Z=4 and T=293K.The structure was solved using heavy-atom techniques and refined by least-squares methods to a residual R value of 0.050.The copper ion is in a centrosymmetric distorted octahedral environment with all chemically identical donor atoms in trans positions.The tetrafluoroborate anions are coordinated to the copper ion with relatively short distances, i.e. 2.55 Angstroem; Cu-N and Cu-S distances are 1.93 Angstroem and 2.41 Angstroem.
- Tullemans, A. H. J.,Bouwman, E.,Graaff, R. A. G. de,Driessen, W. L.,Reedijk, J.
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- Mechanistic studies of the oxidative-coupling polymerization of 2,6-dimethylphenol. Part II. Specifity of the reaction and formation of diphenoquinone
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Copper-(N,N,N',N'-tetramethylenediamine) (tmed) complexes as catalysts in the oxidative-coupling polymerization of 2,6-dimethylphenol (DMP) give rise to poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in high yield, although the formation of the undesired 3,5,3',5'-tetramethyldiphenoquinone (DPQ) cannot be completely avoided.At ligand-to-copper ratios lower than 10, the specifity for PPO formation can be raised by increasing the N/Cu ratio and by the addition of a strong base (potassium or lithium hydroxide).However, once a fivefold excess of tmed is used, neither further tmed nor hydroxide addition raises the specifity beyond 97 percent PPO.Using an N/Cu ratio of 10, neither the catalyst concentration nor the DMP concentration has an effect on the product composition.On the basis of the experimental results in this paper, together with those published in the literature, it is concluded that the specificity is not affected by the structure of the copper complex, provided that sufficiently high ligand-to-copper ratios are used.This results in a product formation which always consist of ca. 3 percent of DPQ and 97 percent PPO.The DPQ is formed mainly during the initial stages of the reaction.However, final DPQ yields of up to 45 percent are found for N/Cu 2+ appear to be present under these conditions as deduced from EPR experiments (in addition to polynuclear CuxCly species).Based on this observation, a radical mechanism for DPQ formation, using Cu(med)22+ as oxidation catalyst, is proposed.There are thus two distinct reaction conditions: (1) At high N/Cu ratios, the highly active dinuclear complex yields 97 percent polymer and ca. 3 percent DPQ.In this case, however, factors which would influence the structure or concentration of the catalyst do not appear to affect the specificity. (2) At low N/Cu ratios, the presence of high concentrations of mononuclear Cu(med)22+ results in high yields of DPQ and in this case, the hydroxide concentration strongly affects the specificity.
- Viersen, F. J.,Challa, G.,Reedijk, J.
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- Mushroom tyrosinase catalysed coupling of hindered phenols: A novel approach for the synthesis of diphenoquinones and bisphenols
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An efficient oxidative carbon-carbon coupling of hindered phenols leading to diphenoquinones and bisphenols by mushroom tyrosinase is reported.
- Pandey,Muralikrishna,Bhalerao
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p. 3771 - 3774
(2007/10/02)
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- Reaction aspects of a μ-peroxo binuclear copper(II) complex
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The reactivity of a μ-peroxo binuclear copper(II) complex [Cu(HB(3,5-Me2Pz)3)]2(O2) (1) toward a variety of substrates is described. PPh3 and CO are not oxidized by 1; they generate mononuclear copper(I) complexes Cu(L)(HB(3,5-Me2pz)3) (L = CO, PPh3) via displacement reactions. Cyclohexene is oxidized to oxygenated products such as 2-cyclohexen-1-ol only under aerobic conditions, and labeling experiments established that the oxygen atoms incorporated into the products come from the exogeneous dioxygen, not from the peroxide ion in the μ-peroxo complex. Phenols and a catechol are oxidatively coupled under anaerobic conditions, while under a dioxygen atmosphere, both oxidatively coupling and oxygenation to give benzoquinones are observed. On the basis of kinetic results, a mechanism is proposed for the oxygenation reactions in which homolytic cleavage of the O-O bond in the μ-peroxo complex is followed by free radical chain reactions with dioxygen.
- Kitajima, Nobumasa,Koda, Takayuki,Iwata, Yusaku,Moro-oka, Yoshihiko
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p. 8833 - 8839
(2007/10/02)
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- Kinetic proof that the tetranuclear oxocopper(II) complex (py)3Cu4Cl4O2 initiates and catalyzes the oxidative coupling of 2,6-dimethylphenol by dioxygen in nitrobenzene
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Copper(I) chloride reacts with equimolar pyridine, py, in ambient-temperature nitrobenzene under dinitrogen to give solutions of the tetranuclear copper(I) complex (py)4Cu4Cl4 (I). Stoichiometric, cryoscopic, and kinetic measurements indicate that I is oxidized to the tetranuclear oxocopper(II) complex (py)4Cu4Cl4O2 (IIa) by dioxygen in nitrobenzene in a second-order process whose rate is independent of the concentration of 2,6-dimethylphenol, [DMP]. Insertion of O2 into the tetranuclear halo core of I is the proposed rate-determining step. Slurry oxidation of CuCl with dioxygen at the molar ratio [py]/[CuCl] = 0.75 in nitrobenzene gives the tetranuclear oxocopper(II) complex (py)3Cu4Cl4O2 (IIb). The rate of direct, first-order oxidation of excess DMP to stoichiometric yields of 3,3′,5,5′-tetramethyl-1,4-diphenoquinone (DPQ) and water by IIa or IIb (9.45 × 10-5 M) in nitrobenzene is independent of which oxidant is used, of [DMP]0 = (2.2-12.2) × 10-3 M, and of [O2]. The system becomes catalytic at higher [DMP]0 or lower [II]0 because destruction of II and inhibition of copper(I) reoxidation by coproduct water are prevented through interaction of the latter with excess phenol. Data at different [DMP] indicate that conversion of a strong complex of stoichiometry IIb-2DMP to products DPQ, water, and copper(I) is the rate-determining catalytic step. Properties of IIa and IIb likely to be responsible for this behavior are discussed.
- El-Sayed, Mohamed A.,Abu-Raqabah, Atieh,Davies, Geoffrey,El-Toukhy, Ahmed
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p. 1909 - 1914
(2008/10/08)
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- THE CHEMISTRY OF PENTAVALENT ORGANOBISMUTH REAGENTS. PART XI. REACTIONS WITH STERICALLY HINDERED PHENOLS.
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The reactivity of BiV reagents towards very hindered phenols with tert.-butyl groups at 2 and 6 under basic conditions has been studied.Unexpected phenylation at the 4-position and, in several cases, replacement of a tert.-butyl group by phenyl have been observed.The mechanism of these unexpected reactions has been discussed.
- Barton, Derek H. R.,Finet, Jean-Pierre,Gianotti, Charles,Halley, Frank
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p. 4483 - 4494
(2007/10/02)
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- Applications of Phase Transfer Catalysis, 33. On the Extraction of Peroxosulfates into Organic Media and on the Oxidative Phenol Coupling by Peroxodisulfate
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Salts of the types (NR4)2S2O8 and NR4HSO5 can be prepared easily by ion pair extraction.The lipophilicity of persulfate anions is classified.Phase transfer catalyzed peroxodisulfate oxidation of 2,6-disubstituted phenols yields diphenoquinones. - Keywords: Lipophilicity, Diphenoquinones, Peroxosulfates, Phase Transfer Catalysis
- Dehmlow, Eckehard V.,Vehre, Burkhard,Makrandi, Jagdish K.
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p. 1583 - 1585
(2007/10/02)
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- STERIC AND ELECTRONIC EFFECTS OF LIGAND VARIATION ON COBALT DIOXYGEN CATALYSTS
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We report herein the observation that electronic and steric factors of cobalt dioxygen complexes with systematically derivatized pentadentate Schiff-base ligands affects their ability to catalyze the oxidation of sustituted phenols and alter the rate of catalyst decomposition.The electronic and steric factors can be separated sufficiently to indicate that the activity of the cobalt dioxygen catalyst roughly parallels the trends in basicity of the bound O2 suggested by EPR cobalt hyperfine coupling constants of the adducts and predicted from the electronic effects of substituents.
- Corden, Barry B.,Drago, Russel S.,Perito, Richard P.
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p. 2903 - 2907
(2007/10/02)
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