- CPMAS 13C NMR Spectra of Quinones, Hydroquinones, and Their Complexes. Use of CMR To Follow a Reaction in the Solid State
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CPMAS 13C NMR spectroscopy has been employed to follow the reaction at temperatures above 70 deg C of the crystalline 1/1 complex of 1,4-benzoquinone with 2,5-dimethyl-1,4-hydroquinone to give the 1/2 complex of 2,5-dimethyl-1,4-benzoquinone-hydroquinone and an equimolar amount of 2,5-dimethyl-1,4-benzoquinone.The redox reaction of a solid mixture of quinhydrone (1,4-benzoquinone-1,4-hydroquinone) with an equimolar amount of 2,5-dimethyl-1,4-hydroquinone gives the 1/2 complex of 2,5-dimethyl-1,4-benzoquinone with 1,4-hydroquinone with no evidence of formation of side products or accumulation of reaction intermediates.During preparation of a mixture of the 1/1 complex of 1,4-benzoquinone-2,5-dimethylhydroquinone with an equimolar amount of 1,4-hydroquinone the partial exchange of one hydroquinone for another in the complex occurs even during mixing of the components at room temperature.An equimolar mixture of 1,4-benzoquinones, 1,4-hydroquinone, and 2,5-dimethyl-1,4-hydroquinone underwent partial complexation at room temperature.These latter two mixtures when heated in the solid state each gave the 1/2 complex 2,5-dimethyl-1,4-benzoquinone-1,4-hydroquinone.As background for this work, CMR spectra of some crystalline quinones, hydroquinones, and their complexes (quinhydrones) have been obtained.The differences between the solid-state and corresponding solution spectra have been shown to be primarily in the multiplicities of some resonances but not others.It is suggested that a primary source of multiplicities in the quinones is CH---O interactions of the sort discussed by others in the analysis of the crystal packing patterns of such compounds.
- Scheffer, J. R.,Wong, Y.-F.,Patil, A. O.,Curtin, D. Y.,Paul, I. C.
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- A CONVENIENT SYNTHESIS OF ALKYL-SUBSTITUTED p-BENZOQUINONES FROM PHENOLS BY A H2O2/HETEROPOLYACID SYSTEM
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Alkyl-substituted p-benzoquinones were easily synthesized in good yields by the oxidation of the corresponding phenols with a hydrogen peroxide/heteropolyacid couple in acetic acid
- Shimizu, Masao,Orita, Hideo,Hayakawa, Takashi,Takehira, Katsuomi
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- 1,3-Dipolar Cycloreversion of the 1-Pyrazoline from 5-Diazo-10,11-dihydro-5H-dibenzocycloheptene and 2,5-Dimethyl-1,4-benzoquinone
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Thermolysis of the pyrazoline formed from 5-diazo-10,11-dihydro-5H-dibenzocycloheptene and 2,5-dimethyl-1,4-benzoquinone gives the component diazoalkane and quinone via 1,3-dipolar cycloreversion, in competition with nitrogen extrusion to give the cyclopropane derivative.
- Oshima, Takumi,Nagai, Toshikazu
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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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- Dimethyl sulfoxide and anhydrous copper (II) sulfate as alkylating reagent for 1,4-quinones
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1,4-Quinones and its derivatives have been alkylated by dimethyl sulfoxide in the presence of anhydrous copper (II) sulfate at the active quinonoid position selectively, in a facile single step reaction with good yields.
- Bansal,Thapliyal,Khanna
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- Quinone tailored selective oxidation of methane over palladium catalyst with molecular oxygen as an oxidant
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With the in situ generated H2O2 tailored by the addition of p-tetrachlorobenzoquinone, the product can be effectively steered towards either HCOOH or the methanol derivative CF3COOCH3 during the direct oxidation of methane with molecular oxygen over palladium catalyst.
- Fan, Yafang,An, Zengjian,Pan, Xiulian,Liu, Xiumei,Bao, Xinhe
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- Electrochemical oxidation of Δ9-tetrahydrocannabinol: a simple strategy for marijuana detection
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Recently, it has been estimated that nearly 200 million people use marijuana with growing usage being attributed to the legalization and decriminalization of the drug around the world. A concerning implication of increased marijuana use is the alarming number of individuals who report driving under the influence of the drug, which has prompted the development of detection technologies. An electrochemical-based detection technology, akin to how the alcohol breathalyzer functions, would provide an attractive solution to this growing societal problem. The first step toward this goal is to develop a reaction that converts Δ9-tetrahydrocannabinol (Δ9-THC), the primary psychoactive substance in marijuana, to a derivative with diagnostic spectroscopic changes. We report the development of a mild electrochemical method for the oxidation of Δ9-THC to its corresponding p-quinone isomer. The photophysical and electrochemical properties of the resultant quinone show a dramatic shift in comparison to Δ9-THC. This simple protocol provides the foundation for the development of an electrochemical-based marijuana breathalyzer.
- Darzi, Evan R.,Garg, Neil K.
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- Efficient Metal-Free Catalytic Reaction Pathway for Selective Oxidation of Substituted Phenols
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Selective oxidation of substituted phenols to p-benzoquinones is known to be inefficient because of the competing C-O coupling reaction caused by phenoxy radicals. The poor stability of conventional metal-based catalysts represents another bottleneck for industrial application. Here, we describe a metal-free reaction pathway in which onion-like carbon (OLC) as a low-cost catalyst exhibits excellent catalytic activity and stability in the selective oxidation of mono-, di- and trisubstituted phenols to their corresponding p-benzoquinones, even better than the reported metal-based catalysts (e.g., yield, stability) and industrial catalysts for particular substrates. Together with XPS, Raman, DFT calculations, and a series of comparative experiments, we demonstrate that the zigzag configuration as a type of carbon defects may play a crucial role in these reactions by stabilizing the intermediate phenoxy radicals.
- Lin, Yangming,Li, Bo,Feng, Zhenbao,Kim, Yoong Ahm,Endo, Morinobu,Su, Dang Sheng
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- PHOTOOXIDATION OF 2,3,6-TRIMETHYLPHENOL
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The present invention relates to the photooxidation of 2,3,6-trimethyl- phenol to yield 2,3,5-trimethylbenzoquinone using methylene blue as photo- sensitizer in a solvent mixture of water and alcohols using light of the high wave- length range of the visible spectrum.
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(2021/11/26)
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- PHOTOOXIDATION OF PHENOLIC COMPOUNDS
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The present invention relates to the photooxidation of phenolic compounds to the respective quinoid compounds using methylene blue as photosensitizer in a solvent mixture of water and alcohols using light of the high wavelength range of the visible spectrum.
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(2021/11/26)
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- PHOTOOXIDATION OF 2,3,5-TRIMETHYLPHENOL
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The present invention relates to the photooxidation of 2,3,5-trimethyl- phenol to yield 2,3,5-trimethylbenzoquinone using methylene blue as photo- sensitizer in a solvent mixture of water and alcohols using light of the high wavelength range of the visible spectrum.
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Page/Page column 14-17
(2021/11/26)
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- Polyoxometalate-based supramolecular porous frameworks with dual-active centers towards highly efficient synthesis of functionalized: P -benzoquinones
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Selective oxidation of substituted phenols is an ideal method for preparing functionalized p-benzoquinones (p-BQs), which serve as versatile raw materials for the synthesis of a variety of biologically active compounds. Herein, two new polyoxometalate-based supramolecular porous frameworks, K3(H2O)4[Cu(tza)2(H2O)]2[Cu(Htza)2(H2O)2][BW12O40]·6H2O (1) and H3K3(H2O)3[Cu(Htza)2(H2O)]3[SiW12O44]·14H2O (2) (Htza = tetrazol-1-ylacetic acid), were synthesized and structurally characterized by elemental analysis, infrared spectroscopy, thermal analysis, UV-vis diffuse reflectance spectroscopy, and single-crystal X-ray and powder diffraction. The single-crystal X-ray diffraction analysis indicates that both compounds possess unique petal-like twelve-nucleated Cu-organic units composed of triangular and hexagonal metal-organic loops. In 1, the Cu-organic units are isolated and [BW12O40]5- polyoxoanions are sandwiched between staggered adjacent triangular channels in the structure. However in 2, the Cu-organic units extend into a two-dimensional layered structure, and the [SiW12O44]12- polyoxoanions occupy the larger hexagonal channels in the stacked structure. Both compounds as heterogeneous catalysts can catalyze the selective oxidation of substituted phenols to high value-added p-BQs under mild conditions (60 °C) with TBHP as the oxidant, particularly in the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone (TMBQ, key intermediate in vitamin E production). Within 8-10 min, the yield of TMBQ is close to 100%, and oxidant utilization efficiency is up to 94.2% for 1 and 90.9% for 2. The turnover frequencies of 1 and 2 are as high as 5000 and 4000 h-1, respectively. No obvious decrease in the yield of TMBQ was observed after five cycles, which indicates the excellent sustainability of both compounds. Our study of the catalytic mechanism suggests that there is a two-site synergetic effect: (i) the copper ion acts as the catalytic site of the homolytic radical pathway; and (ii) the polyoxoanion acts as the active center of the heterolytic oxygen atom transfer pathway. This journal is
- An, Haiyan,Chang, Shenzhen,Chen, Yanhong,Huang, Yaohui,Luo, Huiyun,Zhu, Qingshan
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p. 8591 - 8603
(2021/11/17)
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- Organophotocatalytic Aerobic Oxygenation of Phenols in a Visible-Light Continuous-Flow Photoreactor
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A mild photocatalytic phenol oxygenation enabled by a continuous-flow photoreactor using visible light and pressurized air is described herein. Products for wide-ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p-quinols contributes to sustainable synthesis.
- Wellauer, Jo?l,Miladinov, Dragan,Buchholz, Thomas,Schütz, Jan,Stemmler, René T.,Medlock, Jonathan A.,Bonrath, Werner,Sparr, Christof
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supporting information
p. 9748 - 9752
(2021/05/27)
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- Can Donor Ligands Make Pd(OAc)2a Stronger Oxidant? Access to Elusive Palladium(II) Reduction Potentials and Effects of Ancillary Ligands via Palladium(II)/Hydroquinone Redox Equilibria
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Palladium(II)-catalyzed oxidation reactions represent an important class of methods for selective modification and functionalization of organic molecules. This field has benefitted greatly from the discovery of ancillary ligands that expand the scope, reactivity, and selectivity in these reactions; however, ancillary ligands also commonly poison these reactions. The different influences of ligands in these reactions remain poorly understood. For example, over the 60-year history of this field, the PdII/0 redox potentials for catalytically relevant Pd complexes have never been determined. Here, we report the unexpected discovery of (L)PdII(OAc)2-mediated oxidation of hydroquinones, the microscopic reverse of quinone-mediated oxidation of Pd0 commonly employed in PdII-catalyzed oxidation reactions. Analysis of redox equilibria arising from the reaction of (L)Pd(OAc)2 and hydroquinones (L = bathocuproine, 4,5-diazafluoren-9-one), generating reduced (L)Pd species and benzoquinones, provides the basis for determination of (L)PdII(OAc)2 reduction potentials. Experimental results are complemented by density functional theory calculations to show how a series of nitrogen-based ligands modulate the (L)PdII(OAc)2 reduction potential, thereby tuning the ability of PdII to serve as an effective oxidant of organic molecules in catalytic reactions.
- Bruns, David L.,Musaev, Djamaladdin G.,Stahl, Shannon S.
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supporting information
p. 19678 - 19688
(2020/12/18)
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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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- Catalytic oxidation of aromatic hydrocarbons by a molecular iron-NHC complex
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An iron-NHC complex bearing a tetradentate bis(N-heterocyclic carbene) ligand is applied as catalyst for the oxidation of methyl substituted arene substrates. Using hydrogen peroxide as the oxidant p-xylene and pseudocumene are converted to the corresponding phenols and benzoquinones. The influence of various reaction parameters like temperature, catalyst loading, and oxidant concentration is investigated and kinetic experiments reveal that a temperature reduction leads to an increased catalyst lifetime. Furthermore, an interesting selectivity towards unexpected phenolic products resulting from a methyl shift reaction is observed.
- Lindhorst, Anja C.,Schütz, Jan,Netscher, Thomas,Bonrath, Werner,Kühn, Fritz E.
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p. 1902 - 1911
(2017/07/15)
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- Oxidation of aromatic compounds by hydrogen peroxide catalyzed by mononuclear iron(III) complexes
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In the present work, four mononuclear iron(III) complexes containing BMPA (BMPA?=?bis-(2-pyridylmethyl)amine) and derivative ligands, have been studied as catalyst in toluene oxidation, at 25?°C and 50?°C, using hydrogen peroxide as oxidant and acetonitrile as solvent. All catalysts were able to oxidize toluene with satisfactory yields, producing o-, m-, p-cresols, benzaldehyde and benzyl alcohol, as main products, and traces of 2-methylbenzoquinone and benzoic acid. The catalyst [Fe(BMPA)Cl3] presented the most promising results, reaching yields up to 30.2% at 50?°C after 24?h. Furthermore, [Fe(BMPA)Cl3] was applied in the oxidation of other aromatic compounds as benzene, ethylbenzene, cumene, n-propylbenzene, p-xylene and anisole. The reaction with H2O2 was monitored by electronic UV–vis spectroscopy in the presence and absence of toluene and its oxidation products, as well as by ESI-(+)-MS/Q-TOF mass spectrometry, in order to provide some information about the reaction mechanism.
- Silva, Giselle C.,Carvalho, Nakédia M.F.,Horn, Adolfo,Lachter, Elizabeth R.,Antunes, Octavio A.C.
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p. 564 - 571
(2016/12/16)
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- Catalytic activity of Fe-porphyrins grafted on multiwalled carbon nanotubes in the heterogeneous oxidation of sulfides and degradation of phenols in water
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A biomimetic heterogeneous catalyst was prepared by immobilization of meso-tetrakis(4-carboxyphenyl)porphyrinatoiron(III) chloride (Fe(TCPP)Cl) on multiwalled carbon nanotubes (MWCNTs). The anchored catalyst was characterized by transmission electron microscopy, powder X-ray diffraction, ultraviolet–visible, and Fourier transform infrared spectroscopy. The amount of Fe-porphyrin loaded on the nanotubes was estimated by atomic absorption spectroscopy The thermogravimetric analysis demonstrated that the catalyst was thermally stable up to almost 350 °C, exhibiting high thermal stability. Oxidation of sulfides and phenols with urea hydrogen peroxide (UHP) in water was efficiently enhanced with excellent selectivity under the influence of [Fe(TCPP)Cl@MWCNT]. The title heterogeneous catalytic system facilitates a greener reaction because the reaction solvent is water and UHP is used as a safe oxidant.
- Rayati, Saeed,Nejabat, Fatemeh
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p. 967 - 974
(2017/09/26)
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- Highly Selective and Efficient Ring Hydroxylation of Alkylbenzenes with Hydrogen Peroxide and an Osmium(VI) Nitrido Catalyst
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The OsVI nitrido complex, OsVI(N)(quin)2(OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.
- Kwong, Hoi-Ki,Lo, Po-Kam,Yiu, Shek-Man,Hirao, Hajime,Lau, Kai-Chung,Lau, Tai-Chu
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supporting information
p. 12260 - 12263
(2017/09/06)
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- The Diels-Alder reactions of para-benzoquinone nitrogen-derivatives: An experimental and theoretical study
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An experimental and theoretical study of the comparative reactivity and selectivity of the Diels-Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent parabenzoquinones. DFT calculations support these experimental results.
- Uliana, Marciana P.,Servilha, Bruno M.,Alexopoulos, Olga,De Oliveira, Kleber T.,Tormena, Cláudio F.,Ferreira, Marco A.B.,Brocksom, Timothy J.
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p. 6963 - 6973
(2015/11/09)
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- μ-oxo-bridged hypervalent iodine(III) compound as an extreme oxidant for aqueous oxidations
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We have found that in aqueous oxidations the -oxo-bridged hypervalent iodine trifluoroacetate reagent 1 {[(PhI(OCOCF]} is generally more reactive than the corresponding monomeric reagent, especially toward phenolic substrates. -Oxo-bridged 1 in aqueous media thus provided dearomatized quinones 3 in excellent yields in most cases compared to conventional phenyliodine(III) diacetate and bis(trifluoroacetate), as a result of the rapid oxidation of both phenols and naphthols 2. Furthermore, the oxidation reactions proceeded even in water using water-soluble -oxo oxidant 1, which has promise for -oxo-bridged reagent 1 to become the favored reagent over hydrophobic phenyliodine(III) diacetate and bis(trifluoroacetate). Georg Thieme Verlag Stuttgart New York.
- Dohi, Toshifumi,Nakae, Tomofumi,Takenaga, Naoko,Uchiyama, Teruyoshi,Fukushima, Kei-Ichiro,Fujioka, Hiromichi,Kita, Yasuyuki
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experimental part
p. 1183 - 1189
(2012/05/19)
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- Electrochemical "switching" of Si(100) modular assemblies
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We report on a modular approach for producing well-defined and electrochemically switchable surfaces on Si(100). The switching of these surfaces is shown to change a Si(100) surface from resistant to cell adsorption to promoting cell adhesion. The electrochemical conversion of the modified electrode surface is demonstrated by X-ray photoelectron spectroscopy, X-ray reflectometry, contact angle and cell adhesion studies.
- Ciampi, Simone,James, Michael,Le Saux, Guillaume,Gaus, Katharina,Justin Gooding
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supporting information; experimental part
p. 844 - 847
(2012/03/07)
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- Chemo- and regioselective direct hydroxylation of arenes with hydrogen peroxide catalyzed by a divanadium-substituted phosphotungstate
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Peroxide in, phenol out: The catalyst [-PW10O38V 2(μ-OH)2]3- showed high activity in the hydroxylation of various aromatic compounds with aqueous H2O 2. The system was regioselective, producing para-phenols from monosubstituted benzene derivatives. Furthermore, alkylarenes with reactive side-chain Ca spa 3-H bonds could be chemoselectively hydroxylated without significant formation of side-chain oxygenated products. Copyright
- Kamata, Keigo,Yamaura, Taiyo,Mizuno, Noritaka
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supporting information; experimental part
p. 7275 - 7278
(2012/08/28)
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- A novel process for selective Ruthenium-Catalyzed oxidation of naphthalenes and phenols
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Arenes are selectively oxidized to the corresponding quinones employing ruthenium(2,2′,6′:2″-terpyridine)(2,6-pyridinedicarboxylate) [Ru(tpy)(pydic] as catalyst and hydrogen peroxide as the terminal oxidant. Applying alkylated naphthalenes and phenols, benzo- and naphthoquinones are obtained in up to 93% yield. The industrially interesting oxidation of 2-methylnaphthalene gave 74% of the corresponding quinones and 60% of menadione (vitamin K3). 2,3,5-Trimethylbenzoquinone which constitutes the key intermediate for vitamin E is obtained in 83% yield.
- Wienhoefer, Gerrit,Schroeder, Kristin,Moeller, Konstanze,Junge, Kathrin,Beller, Matthias
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scheme or table
p. 1615 - 1620
(2010/09/05)
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- Selective iron-catalyzed oxidation of phenols and arenes with hydrogen peroxide: Synthesis of vitamin e intermediates and vitamin k3
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(Figure Presented). Pumping iron! Convenient iron-based catalyst systems for the selective oxidation of arenes and phenols with hydrogen peroxide to give 1, 4-quinones have been developed. This selective oxidation reaction takes place under mild conditions (room temperature, alcoholic solvents) with H 2O2 as the terminal oxidant.
- Moeller, Konstanze,Wienhoefer, Gerrit,Schroeder, Kristin,Join, Benoit,Junge, Kathrin,Beller, Matthias
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experimental part
p. 10300 - 10303
(2010/10/21)
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- C-D-glucopyranosyl derivatives of tocopherols - Synthesis and evaluation as amphiphilic antioxidants
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Treatment of dimethylhydroquinone dimethyl ethers (ortho and meta isomers) with glycopyranose pentaacetates (D-gluco, D-galacto) in the presence of SnCl4 and F3CCO2Ag selectively afforded the corresponding C-β-D-glycosyl derivatives by aromatic electrophilic substitution. Oxidation of the dimethoxybenzene moiety with ceric ammonium nitrate delivered C-β-D-glycosyl-dimethylbenzoquinones, which were reduced with Na2S2O4 to the corresponding C-β-D-glycosyldimethylhydroquinones. ZnCl2-catalyzed cyclization either with methylbut-2-en-1-ol (prenyl alcohol) or with all-racemic phytol led to acetyl-protected C-β-D-glycosyl chromanols or C-β-D-glycosyl tocopherols, the sugar residues of which were deacetylated under base catalysis conditions. These new molecules were evaluated as antioxidants in terms of their ability to inhibit the peroxidation of linoleic acid in SDS micelles. The position of the C-glucosyl moiety on the phenolic nucleus emerges as the critical structural determinant of their activity. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- He, Li,Galland, Stephanie,Dufour, Claire,Chen, Guo-Rong,Dangles, Olivier,Fenet, Bernard,Praly, Jean-Pierre
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experimental part
p. 1869 - 1883
(2009/04/04)
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- Preparation of 1,4-hydrobenzoquinones by the PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2-diols
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The PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2- diols, which were easily prepared by the two-step sequence of α-hydroxylation of various conjugated cyclohexenones and the subsequent nucleophilic carbonyl addition of alkyl anions, produced diversely substituted 1,4-hydrobenzoquinones. The Royal Society of Chemistry 2005.
- Kim, Hee Jin,Koo, Sangho
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p. 3479 - 3481
(2007/10/03)
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- The chain mechanism of the reaction between 2,5-dimethyl-1,4-hydroquinone and N-Phenyl-1,4-benzoquinonemonoimine
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The kinetic characteristics of the reaction between N-phenyl-1,4- benzoquinonemonoimine and 2,5-dimethyl-1,4-hydroquinone were studied in chlorobenzene at 298.2 K. The reaction was shown to follow a chain mechanism, the chain length being ～102 units. The rate constants for the elementary reaction steps and the effective reaction orders with respect to the components were determined, and the chain lengths at various concentrations were calculated. A comparison of these data with those obtained earlier for a similar reaction between N-phenyl-1,4-benzoquinonemonoimine and 2,5-di-tert-butyl-1,4-hydroquinone led us to conclude that small changes in the nature of hydroquinone substituents strongly influenced the kinetic parameters of this new class of chain reactions.
- Antonov,Varlamov
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p. 721 - 725
(2007/10/03)
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- Kinetics of oxidation of hydroquinones by molecular oxygen. Effect of superoxide dismutase
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The kinetics of the autoxidation of sixteen hydroquinones (QH2) (substituted 1,4-hydroquinones and 1,4-dihydroxynaphthalenes as well as 9,10-dihydroxyphenanthrene) were studied using the Clark electrode technique in aqueous solution, pH 7.40, at 37°C both with and without added superoxide dismutase (SOD). QH2 oxidation occurs typically with a self-acceleration. A maximum rate of oxidation, RMAX, was found to be the most indicative parameter characterizing QH2 oxidizability. A kinetic scheme of QH2 autoxidation was developed; computer simulations carried out on the basis of this scheme reproduce the main kinetic features of the studied process. QH2 autoxidation is suggested to be a free-radical chain process with semiquinone (Q-) and superoxide (O2-) as chain-carrying species. The oxidation is initiated by reaction (1) Q + QH2→2Q- + 2H+. The addition of SOD results in two main effects: shifting the equilibrium (2) Q- + O2?Q + O2- (K2) to the right and suppressing reaction (3) QH2 + O2-→Q- + H2O2. The net effect of SOD depends basically on K2. When K2 2 > 0.1, the more SOD inhibits the oxidation, the higher K2. The concentration of SOD causing the 50%-effect on RMAX ([SOD]50), both inhibitory and stimulatory, decreases dramatically when K2 increases. At [SOD] ? [SOD]50 the rate of QH2 autoxidation is definitively determined by the rate of reaction (1). For the majority of QH2, [SOD]50 is significantly less than the physiological values of [SOD] and thus QH2 autoxidation in biological environment is expected to occur in the above kinetically simple mode.
- Roginsky, Vitaly,Barsukova, Tatyana
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p. 1575 - 1582
(2007/10/03)
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- Synthesis of quinones from hydroquinone dimethyl ethers. Oxidative demethylation with cobalt(III) fluoride
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The oxidative demethylation of 1,4-dimethoxynaphthalene and 1,4- dimethoxybenzene derivatives with cobalt(III) fluoride proceeded in good to excellent yield to afford the corresponding naphthoquinone and benzoquinone derivatives.
- Tomatsu, Ayumi,Takemura, Syunji,Hashimoto, Kimiko,Nakata, Masaya
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p. 1474 - 1476
(2007/10/03)
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- Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones
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Absorption spectra and rate constants for the disproportionate of 12 alkyl- and methoxy-substituted semiquinone anion free radicals (Q?-) produced by the one-electron reduction (using CO2?- as a reductant) of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation (using N3? as an oxidant) of the corresponding hydroquinones (QH2) were determined by pulse radiolysis in 50 mM sodium phosphate buffer, pH 7.40 at room temperature. Both spectral and kinetic characteristics of Q?- only moderately depended on whether Q?- was produced from Q or QH2. Spectra of benzosemiquinones display two peaks with maximum at 310-320 nm and ca. 430 nm with the ratio of about 2-2.5. Molar absorption coefficients were determined. Rate constants for Q?- disproportionation (2k1) were correlated with the nature of substituents. While 2k1 was scarcely affected by methyl substitution, Q?- containing isopropyl, tert-butyl and methoxy substituents were visibly more stable than non-substituted and methyl-substituted Q?-.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa,Saran, Manfred
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p. 1835 - 1840
(2007/10/03)
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- Rapid conversion of phenols to p-benzoquinones under acidic conditions with lead dioxide
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Treatment of 4-unsubstituted and 4-halogenated phenols with PbO2 and 70% HClO4 in AcOH afforded the corresponding p-benzoquinones in fair to high yields. The oxidation of 4-substituted 2,6-di-tertbutylphenols 6 with PbO2 and 70% HClO4 in acetone gave 2,6-di-tert-butyl-p-benzoquinone (2).
- Omura, Kanji
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p. 1145 - 1148
(2007/10/03)
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- Hydrogen-bonding and protonation effects in electrochemistry of quinones in aprotic solvents
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Hydrogen-bonding and protonation are fundamental factors controlling potentials and mechanisms in the reduction of quinones. These are studied systematically in benzonitrile, acetonitrile, and dimethylsulfoxide solutions by cyclic voltammetry of a series of quinones of increasing basicity (chloranil to duroquinone in the presence of hydroxylic additives of increasing hydrogen-bonding power (tert-butyl alcohol to hexafluoro-2- propanol) or acidity (trifluoroacetic acid). Electrochemical effects are demonstrated over the complete interaction range, from hydrogen bonding of reduced dianions to protonation of unreduced quinones. With increasing concentrations of additives, three clearly different types of electrochemical behavior are observed for weakly (I), moderately (II) and strongly (III) interacting quinone-additive pairs, as follows: (I) Two well-separated reduction waves, corresponding to formation of quinone mono- and dianions, shift positively, with no loss of reversibility. The second wave is smaller, shifts more strongly, and finally merges with the first. The relative heights of the waves remain constant. (II) The positive shift is accompanied by increasing height of the first peak and broadening and irreversibility of the second wave. (III) One or even two, more positively shifted, new prior waves appear, together with a new anodic wave. In interpreting these phenomena, the role of hydrogen-bonding is clearly distinguished from protonation on the basis of pK(a) values of relevant species, effects of solvent variation, magnitude of potential shifts, and the onset of irreversibility. Type I behavior is attributed to stabilization by hydrogen-bonding of mono- and dianion reduction products; the number of bonds per quinone ion and bonding equilibrium constants are estimated from the shifts in peak potentials with additive concentration. These results are supported by simulating the experimental cyclic voltammograms using these parameters. Type III behavior is assigned to initial hydrogen-bonding or protonation of the quinones. Type II is attributed to a reduction mechanism involving disproportionation of primary radicals, assisted by hydrogenbonding or protonation of the dianion.
- Gupta, Neeraj,Linschitz, Henry
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p. 6384 - 6391
(2007/10/03)
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- Polymer supported vanadium salt as a catalyst for the oxidation of phenols
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Oxidation of substituted phenols to the corresponding quinones are reported using a novel macroporous polymer bound catalyst. The catalyst provides a good conversion and is recyclable.
- Suresh,Skaria, Sunny,Ponrathnam
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p. 2113 - 2117
(2007/10/03)
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- Selective Oxidation of Phenols to Quinones with Hydroperoxides Catalysed by Chromium Silicalite-2
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A chromium-containing medium-pore molecular sieve (Si/Cr> 140) having MEL (CrS-2) topology catalyses selectively the oxidation of various phenols to the corresponding p-quinones with 30% H2O2 or 70% ferf-butyl hydroperoxide (TBHP) as the oxidant.
- Ramani,Suresh,Sasidharan,Sudalai,Chanda, Bhanu M.
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p. 474 - 475
(2007/10/03)
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- Rationale for Predominance of 1,3-Dipolar Cycloreversion in Thermolysis of 3,4-Dihydropyrazole from Ethano-bridged Diphenyldiazomethane and 2,5-Dimethyl-1,4-benzoquinone. An X-Ray Study
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The X-ray crystal structure of the title dihydropyrazole indicates that the steric and ?-conjugative effects associated with the conformational locking of the two phenyl rings are the crucial factors in the predominance of 1,3-dipolar cycloreversion rather than nitrogen extrusion to give the cyclopropane derivative.
- Oshima, Takumi,Kawamoto, Tatsuya,Kuma, Hiro,Kushi, Yoshihiko,Nagai, Toshikazu
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p. 1937 - 1938
(2007/10/02)
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- Selective nitration versus oxidative dealkylation of hydroquinone ethers with nitrogen dioxide
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Various alkyl-substituted p-dialkoxybenzenes (ArH) react readily with nitrogen dioxide (NO2) in dichloromethane solution via either nitration (ArNO2) or oxidative dealkylation to quinones (Q). Spectral transients indicate that these coupled processes proceed from the dialkoxybenzene radical cation (ArH+) formed as the common reactive intermediate from electron-transfer in the disproportionated precursor [ArH, NO+]NO3-. In fast subsequent steps, ArH+ undergoes homolytic coupling with NO2 (which leads to aromatic nitration) and nucleophilic attack of NO3- (which results in oxidative dealkylation). As such, the competition between nitration and oxidative dealkylation is effectively modulated by solvent polarity and added nitrate.
- Rathore,Bosch,Kochi
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p. 6727 - 6758
(2007/10/02)
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- Oxidation of Simple Phenols by a Homobimetallic Cerium(IV)-Calix(8)arene Complex in Conjunction with Hydrogen Peroxide
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Phenolic substrates are regioselectively hydroxylated under mild conditions with a cerium(IV)-calix(8)arene complex.
- Chawla, H. Mohindra,Hooda, Usha,Singh, Veena
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p. 617 - 618
(2007/10/02)
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- Reactive dyestuffs
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Triphendioxazine reactive dyestuffs of the general formula STR1 with the substituent definition given in the description, are outstandingly suitable for dyeing and printing materials containing hydroxyl groups or amide groups. They give red dyeings with high wet- and light-fastnesses.
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- Oxidation of Methoxy- and/or Methyl-Substituted Benzenes and Naphthalenes to Quinones and Phenols by H2O2 in HCOOH
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The oxidation of a number of arenes (methoxybenzenes, methylbenzenes, and naphthalenes) to quinones and phenols by H2O2 in HCOOH has been examined.Methoxybenzenes were much more easily oxidized to p-benzoquinones than methylbenzenes (e.g., 1,3,5-trimethoxybenzene was oxidized to 2,6-dimethoxy-p-benzoquinone in a 75percent yield and 1,2,4-trimethylbenzene to 2,3,5-trimethyl-p-benzoquinone in a 16percent yield).Electron-withdrawing substituents, such as nitro, cyano, and chloro groups, lowered the conversion of reactants and changed the product selectivity from quinones to phenols.Methoxybenzonitriles were oxidized to corresponding phenols in a moder ate yield (e.g., 2,6-dimethoxybenzonitrile to 3-hydroxy-2,6-dimethoxybenzonitrile in a 39percent yield and a 64percent selectivity).
- Orita, Hideo,Shimizu, Masao,Hayakawa, Takashi,Takehira, Katsuomi
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p. 1652 - 1657
(2007/10/02)
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- FORMATION OF DIENONES ON THE REACTION OF CRESOLS, XYLENOLS, AND 2-NAPHTHOL WITH NITROGEN DIOXIDE: OBSERVATION OF KETO TAUTOMERS OF NITROPHENOLS
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Reaction of o- and p-cresol, the xylenols, and 2-naphthol with nitrogen dioxide gives nitrocyclohexadienones and nitrophenols.Secondary nitrodienones, the keto tautomers of the nitrophenols, have been observed in several cases and are intermediates in the formation of the nitrophenols.
- Fischer, Alfred,Mathivanan, N.
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p. 1869 - 1872
(2007/10/02)
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- Efficient Preparation of Some Biologically Active Substances from Natural and Nonnatural Aromatic Compounds by m-Chloroperbenzoic Acid Oxidation
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Six naturally occurring aromatic terpenoids and six nonnatural aromatic compounds were oxidized by m-chloroperbenzoic acid in chloroform to give 1,2- and 1,4-quinones or hydroxylated products in which vitamin K1, insecticidal, piscicidal, and antifungal compounds were included.The present method is advantageous for obtaining different types of natural or nonnatural aromatic products having biological activity from the starting aromatic compounds in a one-step reaction.
- Asakawa, Yoshinori,Matsuda, Reiko,Tori, Motoo,Sono, Masakazu
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p. 5453 - 5457
(2007/10/02)
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- Triphendioxazine dyestuffs
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Triphendioxazine dyestuffs of the formula STR1 having the substituent meanings specified in the descriptive part, are highly suitable for dyeing and printing hydroxyl- or amido-containing materials, in particular fibre materials, and produce wash-fast dyeings and prints.
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- OXIDATION OF AROMATIC AMINES WITH CHROMYL CHLORIDE - I OXYDATION OF AROMATIC PRIMARY AMINES
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The oxidation of aromatic primary amines with chromyl chloride in carbon tetrachloride or chloroform, results in the formation of intermediate solid adducts (Etard adducts) which, on hydrolysis, give azobenzenes(1), 1,4-benzoquinones(2), anilino-1,4-benzoquinones(3), 1,4-benzoquinone anils(4) and anilino-1,4-benzoquinone anils(5) in yields which depend on the position, nature and degree of substitution of the ring.
- Nallaiah, C.,Strickson, J. A.
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p. 4083 - 4088
(2007/10/02)
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- Catalytic Oxidation of Hydroquinones and Naphthalenediols to 1,4-Quinones with H2O2 in the Presence of Chromium (VI) Oxide-Bistributyltin Oxide and an Application to Vitamin K1 Synthesis
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The oxidation of hydroquinones and naphthalenediols to 1,4-quinones was carried out in the presence of a chromium (VI) compound formed from chromium (VI) oxide and bistributyltin oxide with 30percent aqueous H2O2 in benzene-isopropyl ether at 50 deg C.The catalyst was fixed on charcoal and used for the oxidation of dihydrovitamin K1 in ethyl alcohol.
- Inoue, Masami,Uragaki, Toshitaka,Enomoto, Saburo
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p. 2075 - 2078
(2007/10/02)
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- On Dien-Ketenes from o-Quinol-Acetates
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A detailed picture of the photochemistry of o-quinol-acetates is presented. (RS)-6-Acetoxy-6-methyl-, (RS)-6-acetoxy-2,6-dimethyl-, (RS)-6-acetoxy-5,6-dimethyl-, (RS)-6-acetoxy-2,4,6-trimethyl-, (RS)-6-acetoxy-2,3,4,6-tetramethyl-, and (RS)-6-acetoxy-2,3,4,5,6-pentamethyl-2,4-cyclohexadien-1-ones serve as representative educts.There are two separate main photochemical routes conveniently designated as 1(?*,n) or 3(?*,?) tracks.The latter may also be attained by sensitization and leads to phenols.The former, by α-cleavage furnishes dien-ketens as indispensable phototransients.Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced bicyclization stereoselectively furnishes bicyclohex-3-en-2-ones, and multi-step addition of protic nucleophiles stereoselectively gives 1,4-, 1,6- and/or 1,2-adducts.By X-ray analysis or NOE studies, the structure of isolated photoproducts is established.Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates.Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that migth be present.Substituents primarily exert an influence upon the population of the various conformers of the dien-keten.Solvents affect the rate of the divers reaction paths competing for the phototransient.Nucleophiles play more than a trivial role when adducts are formed.With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate - or more general from a linear conjugated cyclohexadienone - is now predictable.
- Quinkert, Gerhard,Kleiner, Erna,Freitag, Bernd-Juergen,Glenneberg, Juergen,Billhardt, Uta-Maria,et al.
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p. 469 - 537
(2007/10/02)
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- The Oxidation of Methylbenzenes and Naphthalenes to Quinones with H2O2 in the Presence of Palladium Catalyst
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Methylbenzenes and naphthalenes were oxidized to quinones with aqueous(60percent) H2O2 in acetic acid in the presence of a 0.24 wtpercent Pd(II)-sulfonated polystyrene type resin.The selectivities to quinones were higher in naphthalenes than in methylbenzenes.Among the naphthalenes used, 2-methylnaphthalene, 2,3-dimethylnaphthalene, and 2,6-dimethylnaphthalene gave 1,4-quinones in good yields (50-64percent).The increase in the reaction temperature increased the selectivity to quinones from 40percent at 20 deg C to 70percent at 70 deg C.
- Yamaguchi, Satoru,Inoue, Masami,Enomoto, Saburo
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p. 2881 - 2884
(2007/10/02)
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- Mechanistic Studies on the Oxidation of Naphthalenes and Methylbenzenes to Quinones with H2O2 in the Presence of Pd(II) Catalysts
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The oxidation of naphthalenes and methylbenzenes to quinones with aqueous 60 percent hydrogen peroxide in the presence of a 0.24 percent Pd(II)-sulfonated polystyrene-type resin catalyst was studied.The presence of electron-donating substituents on carbon-2 of naphthalenes accelerated the oxidation. A reaction path by way of hydroxylated intermediates to the quinones is proposed.By using the MINDO/3 method, quantum chemical indices such as the superdelocalizability for electrophilic species (SEr) and for radical species (SRr), and the net charge (Qr) of naphthalenes, methylbenzenes, and naphthols were calculated.The activity in the above reaction could be explained in terms of both Qr and SEr.The decrease of the selectivity was correlated with side reactions by radical species attacking the sites of largest SRr.Keywords - oxidation; hydrogen peroxide; naphthalene; methylbenzene; palladium catalyst; 1,4-naphthoquinone; sulfonated polystyrene-type resin
- Yamaguchi, Satoru,Shinoda, Hiroyuki,Inoue, Masami,Enomoto, Saburo
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p. 4467 - 4473
(2007/10/02)
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- Periodate Oxidation of 2,5-Dimethylaniline in Aqueous Acetic Acid - A Kinetic and Mechanistic Study
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The kinetics of oxidation of 2,5-dimethylaniline by periodate in (2.5percent, v/v) acetic acid-water medium have been followed spectrophotometrically at 545 nm under pseudo-first order conditions.Reaction rate decreases in dielectric constant and also with increase in ionic strength.The reaction is pH-dependent.Various activation parameters have been evaluated.Main oxidation product is 2,5-dimethyl-p-benzoquinone.Results are interpreted in terms of an ionic mechanism.
- Srivastava, S. P.,Bhattacharjee, G.,Malik, Pratibha
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