- Sc3+ (or HClO4) Activation of a Nonheme FeIII-OOH Intermediate for the Rapid Hydroxylation of Cyclohexane and Benzene
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[Fe(β-BPMCN)(CH3CN)2]2+ (1, BPMCN = N,N′-bis(pyridyl-2-methyl)-N,N′-dimethyl-trans-1,2-diaminocyclo-hexane) is a relatively poor catalyst for cyclohexane oxidation by H2O2 and cannot perform benzene hydroxylation. However, addition of Sc3+ activates the 1/H2O2 reaction mixture to be able to hydroxylate cyclohexane and benzene within seconds at -40 °C. A metastable S = 1/2 FeIII-(η1-OOH) intermediate 2 is trapped at -40 °C, which undergoes rapid decay upon addition of Sc3+ at rates independent of [substrate] but linearly dependent on [Sc3+]. HClO4 elicits comparable reactivity as Sc3+ at the same concentration. We thus postulate that these additives both facilitate O-O bond heterolysis of 2 to form a common highly electrophilic FeVO oxidant that is comparably reactive to the fastest nonheme high-valent iron-oxo oxidants found to date.
- Kal, Subhasree,Draksharapu, Apparao,Que, Lawrence
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Read Online
- Single-step benzene hydroxylation by cobalt(ii) catalysts: Via a cobalt(iii)-hydroperoxo intermediate
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The cobalt(ii) complexes of 4N tetradentate ligands have been synthesized and characterized as the catalysts for phenol synthesis in a single step. The molecular structure of the complexes showed a geometry in between square pyramidal and trigonal bipyramidal (τ, 0.49-0.88) with Co-Namine and Co-NPy bond distances of 2.104-2.254 ? and 2.043-2.099 ?, respectively. The complexes exhibited a Co2+/Co3+ redox potential around 0.489-0.500 V vs. Ag/Ag+ in acetonitrile. The complexes catalyzed hydroxylation of benzene using H2O2 (30%) and afforded phenol selectively as the major product. A maximum yield of phenol up to 29% and turnover number (TON) of 286 at 60 °C, and a yield of 19% and TON of 191 at 25 °C are achieved. This is the highest catalytic performance reported using cobalt(ii) complexes as catalysts to date. This aromatic hydroxylation presumably proceeded via a cobalt(iii)-hydroperoxo species, which was characterized by ESI-MS, and vibrational and electronic spectral methods. The formation of key intermediate [(L)CoIII(OOH)]2+ was accompanied by the appearance of the characteristic O → Co(iii) ligand to metal charge transfer (LMCT) transition around 488-686 nm and vibration modes at 832 cm-1 (O-OH) and 564 cm-1 (Co-O). The geometry of one of the catalytically active intermediates was optimized by DFT and its spectral properties were calculated by TD-DFT calculations. These data are comparable to the experimental observations. The kinetic isotope effect (KIE) values (0.98-1.07) support the involvement of cobalt-bound oxygen species as a key intermediate. Isotope-labeling experiments using H218O2 showed an 89% incorporation of 18O, revealing that H2O2 is the main oxygen supplier for phenol formation from benzene. The catalytic efficiencies of cobalt complexes are tuned by ligand architectures via their geometrical configurations and steric properties.
- Anandababu, Karunanithi,Mayilmurugan, Ramasamy,Muthuramalingam, Sethuraman,Velusamy, Marappan
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p. 2540 - 2548
(2020/05/14)
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- Cu(i) complexes obtained: Via spontaneous reduction of Cu(ii) complexes supported by designed bidentate ligands: Bioinspired Cu(i) based catalysts for aromatic hydroxylation
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Copper(i) complexes [Cu(L1-7)2](ClO4) (1-7) of bidentate ligands (L1-L7) have been synthesized via spontaneous reduction and characterized as catalysts for aromatic C-H activation using H2O2 as the oxidant. The single crystal X-ray structure of 1 exhibited a distorted tetrahedral geometry. All the copper(i) complexes catalyzed direct hydroxylation of benzene to form phenol with good selectivity up to 98%. The determined kinetic isotope effect (KIE) values, 1.69-1.71, support the involvement of a radical type mechanism. The isotope-labeling experiments using H218O2 showed 92% incorporation of 18O into phenol and confirm that H2O2 is the key oxygen supplier. Overall, the catalytic efficiencies of the complexes are strongly influenced by the electronic and steric factor of the ligand, which is fine-tuned by the ligand architecture. The benzene hydroxylation reaction possibly proceeded via a radical mechanism, which was confirmed by the addition of radical scavengers (TEMPO) to the catalytic reaction that showed a reduction in phenol formation. This journal is
- Kumari, Sheela,Muthuramalingam, Sethuraman,Dhara, Ashish Kumar,Singh,Mayilmurugan, Ramasamy,Ghosh, Kaushik
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p. 13829 - 13839
(2020/10/26)
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- Visible-light-promoted aerobic oxidative hydroxylation of arylboronic acids in water by hydrophilic organic semiconductor
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A green and sustainable catalytic system was developed based on perylenediimide (PDI) organic semiconductor for the aerobic oxidative hydroxylation of arylboronic acids in aqueous solution with visible light. By using PDI-SN, a hydrophilic organic semiconductor, which can activate oxygen to produce superoxide radicals in aqueous solution, this reaction proceeds under ambient conditions: water as the solvent and air as the oxidant, giving various phenols as products with high yields. In contrast to methods using organic solvents, this novel process has the potential of green industrial application.
- Yu, Kunyi,Zhang, Hanjie,Sheng, Yuqiang,Zhu, Yongfa
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supporting information
(2020/06/23)
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- Phthalocyanine Zinc-catalyzed Hydroxylation of Aryl Boronic Acids under Visible Light
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A visible-light-promoted aerobic oxidative hydroxylation of boronic acids using phthalocyanine zinc as an easily available photosensitizer has been developed. It provided a direct access to synthesize aliphatic alcohols and phenols from boronic acids. The advantages of this approach included the low catalyst loading (0.5 mol%), high efficient, the use of O2 as an oxygen source, wide substrate range, the simple operational process, and mild conditions. (Figure presented.).
- Luo, Dong-Ping,Huang, Yang-Feng,Hong, Xiao-Yi,Chen, Dingben,Li, Guo-Xing,Huang, Xiao-Bo,Gao, Wen-Xia,Liu, Miao-Chang,Zhou, Yun-Bing,Wu, Hua-Yue
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supporting information
p. 961 - 964
(2019/01/25)
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- Transition-Metal-Free C-C, C-O, and C-N Cross-Couplings Enabled by Light
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Transition-metal-catalyzed cross-couplings to construct C-C, C-O, and C-N bonds have revolutionized chemical science. Despite great achievements, these metal catalysts also raise certain issues including their high cost, requirement of specialized ligands, sensitivity to air and moisture, and so-called "transition-metal-residue issue". Complementary strategy, which does not rely on the well-established oxidative addition, transmetalation, and reductive elimination mechanistic paradigm, would potentially eliminate all of these metal-related issues. Herein, we show that aryl triflates can be coupled with potassium aryl trifluoroborates, aliphatic alcohols, and nitriles without the assistance of metal catalysts empowered by photoenergy. Control experiments reveal that among all common aryl electrophiles only aryl triflates are competent in these couplings whereas aryl iodides and bromides cannot serve as the coupling partners. DFT calculation reveals that once converted to the aryl radical cation, aryl triflate would be more favorable to ipso substitution. Fluorescence spectroscopy and cyclic voltammetry investigations suggest that the interaction between excited acetone and aryl triflate is essential to these couplings. The results in this report are anticipated to provide new opportunities to perform cross-couplings.
- Liu, Wenbo,Li, Jianbin,Querard, Pierre,Li, Chao-Jun
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supporting information
p. 6755 - 6764
(2019/05/06)
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- One step phenol synthesis from benzene catalysed by nickel(ii) complexes
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Nickel(ii)complexes of N4-ligands have been synthesized and characterized as efficient catalysts for the hydroxylation of benzene using H2O2. All the complexes exhibited Ni2+ → Ni3+ oxidation potentials of around 0.966-1.051 V vs. Ag/Ag+ in acetonitrile. One of the complexes has been structurally characterized and adopted an octahedral coordination geometry around the nickel(ii) center. The complexes catalysed direct benzene hydroxylation using H2O2 as an oxygen source and afforded phenol up to 41% with a turnover number (TON) of 820. This is unprecedentedly the highest catalytic efficiency achieved to date for benzene hydroxylation using 0.05 mol% catalyst loading and five equivalents of H2O2. The benzene hydroxylation reaction possibly proceeds via the key intermediate bis(μ-oxo)dinickel(iii) species, which was characterized by HR-MS, vibrational and electronic spectral methods, for almost all complexes. The formation constant of the key intermediate was calculated to be 5.61-9.41 × 10-2 s-1 by following the appearance of an oxo-to-Ni(iii) LMCT band at around 406-413 nm. The intermediates are found to be very short-lived (t1/2, 73-123 s). The geometry of one of the catalytically active intermediates was optimized by DFT and its spectral properties were calculated by TD-DFT calculations, which are comparable to experimental spectral data. The kinetic isotope effect (KIE) values (0.98-1.05) support the involvement of nickel-bound oxygen species as an intermediate. The isotope-labeling experiments using H218O2 showed 92.46% incorporation of 18O, revealing that H2O2 is the key oxygen supplier to form phenol. The catalytic efficiencies of complexes are strongly influenced by the geometrical configuration of intermediates, and stereoelectronic and steric properties, which are fine-tuned by the ligand architecture.
- Muthuramalingam, Sethuraman,Anandababu, Karunanithi,Velusamy, Marappan,Mayilmurugan, Ramasamy
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p. 5991 - 6001
(2019/11/11)
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- C70 Fullerene-Catalyzed Metal-Free Photocatalytic ipso-Hydroxylation of Aryl Boronic Acids: Synthesis of Phenols
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A metal-free C70 fullerene-catalyzed method has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to corresponding phenols under photocatalytic conditions. The reaction proceeds under oxygen atmosphere and the mechanistic study revealed that C70 plays a critical role in the generation of reactive oxygen species in the presence of blue light. Reactions in the presence of 18O-labelled water and oxygen confirmed the generation of reactive oxygen species from oxygen molecule. Amine used as a reductant could be recovered in the form of imine. The current method is also applicable to the synthesis of aryl ethers in one-pot two-step process. (Figure presented.).
- Kumar, Inder,Sharma, Ritika,Kumar, Rakesh,Kumar, Rakesh,Sharma, Upendra
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supporting information
p. 2013 - 2019
(2018/04/02)
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- Specific Enhancement of Catalytic Activity by a Dicopper Core: Selective Hydroxylation of Benzene to Phenol with Hydrogen Peroxide
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A dicopper(II) complex, stabilized by the bis(tpa) ligand 1,2-bis[2-[bis(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane (6-hpa), [Cu2(μ-OH)(6-hpa)]3+, was synthesized and structurally characterized. This complex catalyzed selective hydroxylation of benzene to phenol using H2O2, thus attaining large turnover numbers (TONs) and high H2O2 efficiency. The TON after 40 hours for the phenol production exceeded 12000 in MeCN at 50 °C under N2, the highest value reported for benzene hydroxylation with H2O2 catalyzed by homogeneous complexes. At 22 % benzene conversion, phenol (95.2 %) and p-benzoquinone (4.8 %) were produced. The mechanism of H2O2 activation and benzene hydroxylation is proposed.
- Tsuji, Tomokazu,Zaoputra, Antonius Andre,Hitomi, Yutaka,Mieda, Kaoru,Ogura, Takashi,Shiota, Yoshihito,Yoshizawa, Kazunari,Sato, Hiroyasu,Kodera, Masahito
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supporting information
p. 7779 - 7782
(2017/06/28)
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- METHOD OF PRODUCING PHENOLIC COMPOUND
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PROBLEM TO BE SOLVED: To provide a method of efficiently producing a phenolic compound by direct oxidation of an aromatic compound. SOLUTION: The present invention provides a method of producing a phenolic compound by oxidizing an aromatic compound by an oxidizer in the presence of a copper complex having as a ligand a compound represented by the formula (I) or (II) in the figure. (In the formulas, R1 to R9 each independently represent a methylene group or ethylene group.) SELECTED DRAWING: None COPYRIGHT: (C)2018,JPOandINPIT
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Paragraph 0057; 0058
(2018/03/30)
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- Pd-Catalyzed Hydroxylation of Aryl Boronic Acids Using In Situ Generated Hydrogen Peroxide
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Herein, we describe a benign and efficient palladium-catalyzed hydroxylation of aryl boronic acids under mild conditions, with in situ generated hydrogen peroxide from carbon monoxide, water, and oxygen. This novel procedure combines catalytic production of hydrogen peroxide with an aerobic oxidation process in a sole reaction system. This system shows good functional group tolerance and provides a benign and efficient access to a variety of functionalized phenols. Furthermore, the in situ generated hydroperoxide can be well used for triphenylphosphine oxidation, in which the TON is up to 194. Isotope labelling studies provide important mechanistic insights for this process.
- Yi, Hong,Lei, Aiwen
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supporting information
p. 10023 - 10027
(2017/08/01)
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- CO/O2 assisted oxidative carbon-carbon and carbon-heteroatom bond cleavage for the synthesis of oxosulfonates from DMSO and olefins
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Selective carbon-carbon and carbon-heteroatom bond cleavage was achieved in a one reaction system. With this strategy a novel Pd/Cu-catalyzed aerobic oxidative oxosulfonation of olefins with DMSO has been developed. Preliminary mechanistic investigations indicated that CO/O2 assisted the bond cleavage and the leaving groups from the starting materials were trapped by O2 and underwent a hydroxylation process.
- Shao, Ailong,Gao, Meng,Chen, Songtao,Wang, Tao,Lei, Aiwen
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p. 2175 - 2178
(2017/03/09)
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- Biogenic synthesis of Fe2O3@SiO2 nanoparticles for ipso-hydroxylation of boronic acid in water
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Here, biogenic synthesis of Fe2O3@SiO2 nanoparticles using fruit extract of Zanthoxylum rhetsa is reported. The SiO2 nanoparticles was synthesized using paddy straw which is a byproduct obtained in cultivation of rice. The composite was characterised by spectroscopic method like XRD, SEM, TEM and EDX analysis. The ipso-hydroxylation reactions were carried out with excellent yield within a moderate time period with mild reaction condition in all cases. Therefore, this approach may be considered as simple, easy, cheap and greener, environment friendly protocol for ipso-hydroxylation of arylboronic acids at 50 °C temperature.
- Saikia, Indranirekha,Hazarika, Moushumi,Hussian, Najrul,Das, Manash R.,Tamuly, Chandan
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supporting information
p. 4255 - 4259
(2017/10/11)
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- Rhodium-Catalyzed Double Alkyl-Oxygen Bond Cleavage: An Alkyl Transfer Reaction from Bis/Tris(o-alkyloxyphenyl)phosphine to Aryl Acids
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An unprecedented rhodium-catalyzed selective cleavage of double alkyl-oxygen bonds of bis/tris(o-alkyloxyphenyl)phosphine has been realized, in which P atom functions as a directing group and simple aryl acids are the methyl group acceptor to provide methyl esters and a quaternary phosphonium salt. The preliminary mechanism was investigated via an 18O labeling experiment and stoichiometric reaction between a Rh-A crystal and an aromatic acid.
- Zhou, Hui,Zhang, Jinlong,Yang, Huameng,Xia, Chungu,Jiang, Gaoxi
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supporting information
p. 3406 - 3412
(2016/10/21)
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- Sustainable oxidations with air mediated by gallic acid: Potential applicability in the reutilization of grape pomace
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Gallic acid converts atmospheric oxygen into hydrogen peroxide, which is able to oxidize arylboronic acids as a proof of concept of sustainable oxidations. Moreover, tannic acid and grape pomace extract are also able to perform oxidations with air. Therefore this work unleashes an alternative method for reutilization and valorization of bio-wastes rich in tannins.
- Scoccia, Jimena,Perretti, Marcelle D.,Monzón, Diego M.,Crisóstomo, Fernando P.,Martín, Víctor S.,Carrillo, Romen
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supporting information
p. 2647 - 2650
(2016/06/06)
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- Photocatalytic Hydrogen-Evolution Cross-Couplings: Benzene C-H Amination and Hydroxylation
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We present a blueprint for aromatic C-H functionalization via a combination of photocatalysis and cobalt catalysis and describe the utility of this strategy for benzene amination and hydroxylation. Without any sacrificial oxidant, we could use the dual catalyst system to produce aniline directly from benzene and ammonia, and phenol from benzene and water, both with evolution of hydrogen gas under unusually mild conditions in excellent yields and selectivities.
- Zheng, Yi-Wen,Chen, Bin,Ye, Pan,Feng, Ke,Wang, Wenguang,Meng, Qing-Yuan,Wu, Li-Zhu,Tung, Chen-Ho
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supporting information
p. 10080 - 10083
(2016/09/04)
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- Oxidation with air by ascorbate-driven quinone redox cycling
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Transition metal-free oxidation with air at room temperature has been achieved by simply using ascorbate (vitamin C) and catalytic amounts of menadione (vitamin K3). A combination of the mentioned vitamins transforms atmospheric oxygen into hydrogen peroxide, which is able to oxidize arylboronic acids and other chemical moieties. This journal is
- Silveira-Dorta, Gastón,Monzón, Diego M.,Crisóstomo, Fernando P.,Martín, Tomás,Martín, Víctor S.,Carrillo, Romen
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supporting information
p. 7027 - 7030
(2015/04/22)
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- Oxygenation of Organoboronic Acids by a Nonheme Iron(II) Complex: Mimicking Boronic Acid Monooxygenase Activity
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Phenolic compounds are important intermediates in the bacterial biodegradation of aromatic compounds in the soil. An Arthrobacter sp. strain has been shown to exhibit boronic acid monooxygenase activity through the conversion of different substituted phenylboronic acids to the corresponding phenols using dioxygen. While a number of methods have been reported to cleave the C-B bonds of organoboronic acids, there is no report on biomimetic iron complex exhibiting this activity using dioxygen as the oxidant. In that direction, we have investigated the reactivity of a nucleophilic iron-oxygen oxidant, generated upon oxidative decarboxylation of an iron(II)-benzilate complex [(TpPh2)FeII(benzilate)] (TpPh2 = hydrotris(3,5-diphenyl-pyrazol-1-yl)borate), toward organoboronic acids. The oxidant converts different aryl/alkylboronic acids to the corresponding oxygenated products with the incorporation of one oxygen atom from dioxygen. This method represents an efficient protocol for the oxygenation of boronic acids with dioxygen as the terminal oxidant.
- Chatterjee, Sayanti,Paine, Tapan Kanti
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p. 9727 - 9732
(2015/11/03)
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- Ligand- and base-free synthesis of phenols by rapid oxidation of arylboronic acids using iron(III) oxide
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Fe2O3 catalyzed rapid oxidation of arylboronic acids to obtain phenols in excellent yields (90-95%) in the presence of atmospheric oxygen under solar VIS-light irradiation using α-Fe2O 3 as a catalyst in ligand- and base-free conditions is presented.
- Sawant, Sanghapal D.,Hudwekar, Abhinandan D.,Aravinda Kumar,Venkateswarlu, Vunnam,Singh, Parvinder Pal,Vishwakarma, Ram A.
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p. 811 - 814
(2014/02/14)
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- Highly selective phenol production from benzene on a platinum-loaded tungsten oxide photocatalyst with water and molecular oxygen: Selective oxidation of water by holes for generating hydroxyl radical as the predominant source of the hydroxyl group
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Particles of tungsten oxide loaded with nanoparticulate platinum (Pt/WO3) photocatalytically produced phenol from benzene with high selectivity (e.g., 74% at 69% of benzene conversion) in water containing molecular O2; the selectivity for phenol was much higher than that on conventional titanium oxide (TiO2) photocatalysts (both the unmodified and Pt-loaded) that generated CO2 as a main product. Results confirmed that photoexcited electrons on the Pt/WO3 photocatalysts mainly generated H2O2 from molecular O2 through a two-electron reduction; the H2O2 generated did not significantly contribute to the undesirable peroxidation of the phenol produced. In contrast, the oxygen radical species, such as O2- or HO2, generated on TiO2 photocatalysts partially contributed to the successive oxidation of phenol and other intermediates to reduce the selectivity for phenol. More importantly, the reactions using 18O-labeled O2 and H2O clearly revealed that the holes generated on Pt/WO3 react primarily with H2O molecules, even in the presence of benzene in aqueous solution, selectively generating OH radicals that subsequently react with benzene to produce phenol. In contrast, a portion of the holes generated on TiO2 photocatalysts reacts directly with benzene molecules, which are adsorbed on the surface of TiO2 by strong interaction with surface hydroxyl groups. This direct oxidation of substances by holes undoubtedly enhanced non-selective oxidation, consequently lowering the selectivity for phenol by TiO2. The two unique features of Pt/WO3, the absence of reactive oxygen radical species from O2 and the ability to selectively oxidize water to form OH, are the most likely reasons for the highly selective phenol production. This journal is
- Tomita, Osamu,Ohtani, Bunsho,Abe, Ryu
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p. 3850 - 3860
(2015/02/19)
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- A novel sustainable strategy for the synthesis of phenols by magnetic CuFe2O4-catalyzed oxidative hydroxylation of arylboronic acids under mild conditions in water
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A novel sustainable strategy for the synthesis of phenols has been developed using inexpensive, readily available, air-stable, and recyclable CuFe2O4 nanoparticles as the catalyst, and the corresponding substituted phenols were obtained in moderate to good yields by oxidative hydroxylation of arylboronic acids in water. Importantly, a ligand or an additive was not necessary. The catalyst was completely recoverable with an external magnet and could be reused six times without significant loss of catalytic activity.
- Yang, Daoshan,An, Baojuan,Wei, Wei,Jiang, Min,You, Jinmao,Wang, Hua
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supporting information
p. 3630 - 3634
(2014/05/20)
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- Visible-light-induced oxygenation of benzene by the triplet excited state of 2,3-dichloro-5,6-dicyano-p-benzoquinone
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Photocatalytic oxygenation of benzene to phenol occurs under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in an oxygen-saturated acetonitrile solution of benzene and tert-butyl nitrite. The photocatalytic reaction is initiated by photoinduced electron transfer from benzene to the triplet excited state of DDQ.
- Ohkubo, Kei,Fujimoto, Atsushi,Fukuzumi, Shunichi
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supporting information
p. 5368 - 5371
(2013/06/04)
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- The first general route for efficient synthesis of 18O labelled alcohols using the HOF·CH3CN complex
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A mild and very efficient method for converting boronic acids to alcohols has been developed using the acetonitrile complex of hypofluorous acid HOF·CH3CN. Employing 18O-labeled water results in alcohols containing a heavy oxygen isotope. The reactions were performed at room temperature, within a few minutes and in excellent yields.
- Gatenyo, Julia,Vints, Inna,Rozen, Shlomo
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supporting information
p. 7379 - 7381
(2013/09/23)
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- Synthesis of unsymmetrical biaryl ethers through nickel-promoted coupling of polyfluoroarenes with arylboronic acids and oxygen
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Polyfluoro-substituted unsymmetrical biaryl ethers were synthesized via a novel Ni-catalyzed cross-coupling reaction of polyfluoroarenes with arylboronic acids and oxygen. The polyfluorinated arenes presumably captured the phenoxide intermediate efficiently, which made the oxygen-insertion proceed smoothly via the SNAr protocol. The 18O labeling experiment demonstrated that the oxygen introduced into unsymmetrical diaryl ether originated from very trace amounts of oxygen in the reaction system. A plausible mechanism was also suggested.
- Zhang, Jian,Wu, Jingjing,Xiong, Yang,Cao, Song
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scheme or table
p. 8553 - 8555
(2012/09/22)
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- Determination of oxygen sources for oxidation of benzene on TiO2 photocatalysts in aqueous solutions containing molecular oxygen
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Photocatalytic oxidation of benzene to CO2 was studied in aqueous solutions using different kinds of TiO2 powders, and isotopic oxygen tracers (H218O and 18O2) were used to investigate the oxidation process. Phenol was produced as a main intermediate in solution. When anatase powders, which showed high activity for oxidation of benzene, were used, 70-90% of oxygen introduced into phenol was from water. On the other hand, when rutile powders were used, only 20-40% of the oxygen was from water. The rest was from molecular oxygen in both cases. The rate of phenol production by using molecular oxygen was nearly the same between anatase and rutile powders. Hence, the high activity of anatase powders for oxidation of benzene to CO2 is attributed to their high activity for oxidation of benzene to phenol, which is considered to be the rate-determining step, using water as the oxygen source. The processes using water and molecular oxygen as the oxygen sources are ascribed, respectively, to oxygen transfer and hole transfer processes in the initial step of benzene oxidation.
- Bui, Thuan Duc,Kimura, Akira,Ikeda, Shigeru,Matsumura, Michio
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experimental part
p. 8453 - 8458
(2010/08/04)
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- Aromatic Hydroxylation at a Non-Heme Iron Center: Observed Intermediates and Insights into the Nature of the Active Species
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Mechanism of substrate oxidations with hydrogen peroxide in the presence of a highly reactive, biomimetic, iron aminopyridine complex, [Fe II(bpmen)(CH3CN)2][ClO4] 2 (1; bpmen=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2- diamine), is elucidated. Complex 1 has been shown to be an excellent catalyst for epoxidation and functional-group-directed aromatic hydroxylation using H2O2, although its mechanism of action remains largely unknown.1, 2 Efficient intermolecular hydroxylation of unfunctionalized benzene and substituted benzenes with H2O2 in the presence of 1 is found in the present work. Detailed mechanistic studies of the formation of iron(III)-phenolate products are reported. We have identified, generated in high yield, and experimentally characterized the key FeIII(OOH) intermediate (Imax=560 nm, rhombic EPR signal with g=2.21, 2.14, 1.96) formed by 1 and H2O2. Stopped-flow kinetic studies showed that FeIII(OOH) does not directly hydroxylate the aromatic rings, but undergoes rate-limiting self-decomposition producing transient reactive oxidant. The formation of the reactive species is facilitated by acid-assisted cleavage of the O-O bond in the iron-hydroperoxide intermediate. Acid-assisted benzene hydroxylation with 1 and a mechanistic probe, 2-Methyl-1-phenyl-2-propyl hydroperoxide (MPPH), correlates with O-O bond heterolysis. Independently generated FeIV=O species, which may originate from O-O bond homolysis in FeIII(OOH), proved to be inactive toward aromatic substrates. The reactive oxidant derived from 1 exchanges its oxygen atom with water and electrophilically attacks the aromatic ring (giving rise to an inverse H/D kinetic isotope effect of 0.8). These results have revealed a detailed experimental mechanistic picture of the oxidation reactions catalyzed by 1, based on direct characterization of the intermediates and products, and kinetic analysis of the individual reaction steps. Our detailed understanding of the mechanism of this reaction revealed both similarities and differences between synthetic and enzymatic aromatic hydroxylation reactions.
- Makhlynets, Olga V.,Rybak-Akimova, Elena V.
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experimental part
p. 13995 - 14006
(2011/04/12)
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- Examination of P-OR bridging bond orders in phosphate monoesters using 18O isotope shifts in 31P NMR
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Evidence indicates that phosphate monoesters undergo hydrolysis by a loose transition state with extensive bond fission to the leaving group. It has been proposed that part of the high dependence of the rate on the leaving group pKa (βlg/
- Sorensen-Stowell, Kerensa,Hengge, Alvan C.
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p. 4805 - 4809
(2007/10/03)
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- A Novel Photo-induced Fenton's Reaction. Perfluorinated Poly(p-Phenylene)-catalyzed Photohydroxylation of Benzene with O2 and H2O to Phenol
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18O Tracer study of perfluorinated poly(p-phenylene)-catalyzed photohydroxylation of benzene to phenol with H218O and 16O2 revealed that the hydroxylation initially occurs by the attack of the hydroxyl radical (H18O radical) generated by the photooxidation of H218O, but the hydroxyl radical (H16O radical) derived from the concurrently produced H216O2 comes to participate in further hydroxylation as the photocatalysis proceeds.
- Maruo, Katsuya,Wada, Yuji,Yanagida, Shozo
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p. 565 - 566
(2007/10/02)
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- Palladium catalyzed direct oxidation of benzene with molecular oxygen to phenol
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Direct phenol synthesis from benzene is currently one of the most important problems in modern chemistry. We have reported new phenol synthesis from benzene and O2 via direct activation of a C-H aromatic bond by the Pd(OAc)2/phenanthroline catalyst system. The evidence for direct oxidation of benzene by O2 was obtained using 18O and 2H isotopes. The mechanism was proposed on the basis of these results and the reactions of Ph-Pd σ complex intermediates.
- Jintoku,Takaki,Fujiwara,Fuchita,Hiraki
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p. 438 - 441
(2007/10/02)
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- Synthesis and NMR spectroscopy of stable isotope-labelled phenols and L-tyrosines
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The syntheses of (17O)phenol from (17O)water, (18O)phenol from (18O)water, (1-13C)-phenol and (4-13C)phenol from (2-13C)acetone and (2-13C)phenol and (3-13C)phenol from (1-13C)acetone with high isotopic enrichment are described.The labelled phenols are converted into their corresponding L-tyrosines by the bacterium Erwinia herbicola.A full analysis of the 1H and 13C NMR spectra of phenol and L-tyrosine is reported.
- Winkel, C.,Aarts, M. W. M. M.,Heide, F. R. van der,Buitenhuis, E. G.,Lugtenburg, J.
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p. 139 - 146
(2007/10/02)
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- Thermal and Photochemical Reactions of Triarylmethyl Peroxides
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The thermal and photochemical decomposition products of p-benzoyltriphenylmethyl peroxide (I), of m-benzoyltriphenylmethyl peroxide (II), and of isotopically labeled analogues indicate rapid radical 1,2-migrations precluding other radical processes such as β-elimination from the incipient radical.The mechanism of these processes is interpreted in terms of these rearrangements as well as reversible elimination of O2 from the starting peroxide.Differences in the two isomeric peroxides are assessed.
- Neckers, D.C.,Linden, Shwn-Meei,Williams, B. Lee,Zakrzewski, Andrzej
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p. 131 - 135
(2007/10/02)
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- AN (18)O-TRACER STUDY ON THE TiO2-SENSITIZED PHOTOOXIDATION OF AROMATIC COMPOUNDS
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TiO2-sensitized photooxidation of benzenes has been studied to disclose the origin of the ring hydroxylating species.An (18)O-tracer study using (18)O2 gas revealed that the hydroxyl group of phenols comes essentially from molecular oxygen at higher pH region.At lower pH, however, the oxygen atom in phenols originates mostly from solvent water.These findings are compatible with two different mechanism proposed by Osa et al. and Tokumaru et al.; that is, the major pathway changes with pH.
- Takagi, Katsuhiko,Fujioka, Toshio,Sawaki, Yasuhiko,Iwamura, Hiizu
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p. 913 - 916
(2007/10/02)
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- Absolute rate constants for hydrocarbon autoxidation. 32. On the self-reaction of 1,1-diphenylethylperoxyl in solution
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The major products of the self-reaction of 1,1-diphenylethylperoxyl have been determined from product studies of the autoxidation of 1,1-diphenylethane, induced decomposition of 1,1-diphenylethyl hydroperoxide, and decomposition of 2,2,3,3-tetraphenylbutane under an atmosphere of oxygen.Overall self-reaction is a complex free-radical process involving the intermediacy of 1,1-diphenylethoxyl and 1-phenyl-1-phenoxyethoxyl which undergo H-atom abstraction, β-scission and, in the case of the former radical, rearrangement.Hydroperoxide decomposition under an atmosphere of (36)O2, has shown that 1,1-diphenylethylperoxyl undergoes β-scission faster than α-cumylperoxyl at 303 K in solution.The values of the rate constants for self-reaction of Ph2C(Me)O2. relative to those for the tert-butylperoxyl are, however, not affected by this reaction.Furthermore they are not affected to any appreciable extent by the efficiency with which Ph2C(Me)O. , formed in nonterminating self-reaction, escape from the solvent cage.They are influenced principally by the first-order rate of decomposition of Ph2C(Me)OOOOC(Me)Ph2.
- Howard, J. A.,Chenier, J. H. B.,Yamada, T.
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p. 2566 - 2572
(2007/10/02)
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