- A rapid and efficient synthesis of quinone derivatives: Ru(II)-or Ir(I)-catalyzed hydrogen peroxide oxidation of phenols and methoxyarenes
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Hydroquinone and methoxybenzene derivatives were catalytically oxidized promptly to the corresponding quinones in up to 99% yield. With a catalyst loading of 0.01 mol %, a maximum TON of 8.4 × 103 was attained in the case of Ru(II)-complex. Ru(II)(pybox-dh)(pydic) is able to enhance the hydrogen peroxide oxidation of substituted hydroquinones as well as methoxybenzenes, but Ir[(coe)2Cl]2 and Ir[(cod)Cl] 2 were found to be effective catalysts only for the former substrates under similar oxidation conditions.
- Iwasa, Seiji,Fakhruddin, Ahmad,Widagdo, Herman Setyo,Nishiyama, Hisao
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Read Online
- Oxidation of hydroquinones with meso-hexakispentafluorophenyl [26]hexaphyrin(1.1.1.1.1.1)
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Treatment of various hydroquinones and catechols with meso- pentafluorophenyl [26]hexaphyrin(1.1.1.1.1.1) provided the corresponding quinones quantitatively. The Royal Society of Chemistry 2006.
- Maeda, Chihiro,Shinokubo, Hiroshi,Osuka, Atsuhiro
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Read Online
- Zwitterion-induced organic-metal hybrid catalysis in aerobic oxidation
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In many metal catalyses, the traditional strategy of removing chloride ions is to add silver salts via anion exchange to obtain highly active catalysts. Herein, we reported an alternative strategy of removing chloride anions from ruthenium trichloride using an organic [P+-N-] zwitterionic compound via multiple hydrogen bond interactions. The resultant organic-metal hybrid catalytic system has successfully been applied to the aerobic oxidation of alcohols, tetrahydroquinolines, and indolines under mild conditions. The performance of zwitterion is far superior to that of many other common Lewis bases or Br?nsted bases. Mechanistic studies revealed that the zwitterion triggers the dissociation of chloride from ruthenium trichloride via nonclassical hydrogen bond interaction. Preliminary studies show that the zwitterion is applicable to catalytic transfer semi-hydrogenation.
- Hu, Rong-Bin,Lam, Ying-Pong,Ng, Wing-Hin,Wong, Chun-Yuen,Yeung, Ying-Yeung
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p. 3498 - 3506
(2021/04/07)
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- The impact of an isoreticular expansion strategy on the performance of iodine catalysts supported in multivariate zirconium and aluminum metal-organic frameworks
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Iodine functionalized variants of DUT-5 (Al) and UiO-67 (Zr) were prepared as expanded-pore analogues of MIL-53 (Al) and UiO-67 (Zr). They were prepared using a combination of multivariate and isorecticular expansion strategies. Multivariate MOFs with a 25% iodine-containing linker was chosen to achieve an ideal balance between a high density of catalytic sites and sufficient space for efficient diffusion. Changes to the oxidation potential of the catalyst as a result of the pore-expansion strategy led to a decrease in activity with electron rich substrates. On the other hand, these larger frameworks proved to be more efficient catalysts for substrates with higher oxidation potentials. Recyclability tests for these larger MOFs showed sustained catalytic activity over multiple recycles.
- Tahmouresilerd, Babak,Moody, Michael,Agogo, Louis,Cozzolino, Anthony F.
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supporting information
p. 6445 - 6454
(2019/05/24)
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- A Facile and Selective Procedure for Oxidation of Hydroquinones using Silica Gel Supported Catalytic Cerium(IV) Ammonium Nitrate
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A new procedure for oxidation of hydroquinones to quinones using a silica gel supported cerium(IV) ammonium nitrate-NaBrO3 reagent has been developed. This simple, easy to prepare and use, heterogeneous reagent is highly selective towards oxidation of 1,4-dihydroxybenzenes and produces high yields of quinones. Waste generated by using this procedure is minimal.
- Ali, Mohammed Hashmat,Welker, Andrea,York, Crystal
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p. 3207 - 3211
(2015/10/19)
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- Preparation and catalytic performance of perfluorosulfonic acid-functionalized carbon nanotubes
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Perfluorosulfonic acid-functionalized carbon nanotubes were prepared by liquid deposition of the perfluorosulfonic acid-polytetrafluoroethylene copolymer and characterized by N2 adsorption, scanning electron microscopy, transmission electron mi
- Zhang, Mengxiao,Li, Cuican,Hua, Weiming,Yue, Yinghong,Gao, Zi
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p. 1874 - 1882
(2015/09/28)
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- Homogeneous Pd-catalyzed transformation of terminal alkenes into primary allylic alcohols and derivatives
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Synthesis of primary alcohols from terminal alkenes is an important process in both bulk and fine chemical syntheses. Herein, a homogeneous Pd-complex-catalyzed transformation of terminal alkenes into primary allylic alcohols, by using 5 mol % [Pd(PPh3)4] as a catalyst, and H2O, CO2, and quinone derivatives as reagents, is reported. When alcohols were used instead of H2O, allylic ethers were obtained. A proposed mechanism includes the addition of oxygen nucleophiles at the less-hindered terminal position of π-allyl Pd intermediates.
- Tomita, Ren,Mantani, Kohei,Hamasaki, Akiyuki,Ishida, Tamao,Tokunaga, Makoto
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supporting information
p. 9914 - 9917
(2014/08/18)
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- Enhanced activity over alkyl/aryl functionalized porous pillared-zirconium phosphates in liquid-phase reaction
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A series of porous pillared-zirconium phosphates functionalized with methyl, ethyl, propyl and phenyl groups were prepared and characterized by SEM, 29Si MAS NMR, TG and N2 adsorption. Their total surface acidity and accessible one were measured by potentiometric titration of n-butylamine and liquid phase 2,6-di-tert-butyl-pyridine adsorption, respectively. The catalytic behaviors of these hybrid materials for alkylation of hydroquinone and esterification of lauric acid were compared. Not the total acid sites but the accessible ones play a crucial role in both reactions of alkylation and esterification. The accession for acid sites can be enhanced by the introduction of alkyl/aryl groups, due to the improved hydrophobicity of the surface.
- Liu, Ke,Wang, Xueyan,Ding, Shengda,Li, Ying,Hua, Weiming,Yue, Yinghong,Gao, Zi
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- Quinones synthesis via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by homogeneous and macroporous-polymer-supported ruthenium catalysts
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Ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-Pheox) complex 2a and its macroporous-polymeric-catalyst 4 were found to be very rapid and efficient catalysts in the hydrogen peroxide oxidation of 1,2- and 1,4-dihydroxy arenes. Most of the quinone products were delivered in 99% yield. The polymeric-catalyst 4 could be reused at least five times.
- Abu-Elfotoh, Abdel-Moneim,Tsuzuki, Kazuyuki,Nguyen, Tram Bao,Chanthamath, Soda,Shibatomi, Kazutaka,Iwasa, Seiji
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p. 8612 - 8617
(2013/09/12)
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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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- Redox active donor-substituted punicin derivatives
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The redox active plant material punicin from Punica granatum, 2-hydroxy-1-(pyridinium-1-yl)-5-olate, and some derivatives were modified by substitution with 2-oxochromen-4-olate moieties to give donor-substituted molecules which form distinct types of atropisomeric mesomeric betaines and tetrapolar substances. Oxidation to new negatively-charged solvatochromic quinones was achieved on treatment of these betaines with CAN, taking advantage of the stabilizing properties of the electron-donating 2-oxochromen-4-olate partial structure. The quinones can be employed in model redox reactions. Cyclovoltametric studies have been performed.
- Albrecht, Marcel,Schneider, Oliver,Schmidt, Andreas
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experimental part
p. 1445 - 1453
(2009/12/04)
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- The mediatory activity of Ce(IV)/Ce(III) redox system immobilized in nafion film on glassy carbon
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Properties of the glassy carbon modified with Ce(III) ions immobilized in Nafion film and the catalytic activity of these ions or the catalytic activity of the modified conducting phase in electrochemical oxidation of some hydroquinone, phenylenediamine and 4-hydroxybenzoic acid derivatives were investigated. The redox activity was characterized in aqueous solutions of perchloric acid by cyclic voltammetry. The redox process was diffusion-limited which can suggest that the cerium(III) ions immobilized in the Nafion multilayer was rate-controlling. The increase of anodic peaks of investigated compounds during oxidation on the modified electrode (GC/Nafion/Ce(III)), and drastic decrease of cathodic peak related to Ce(IV) ions reduction, points to the mediatory activity of these ions. The increase of oxidation currents observed during preparative electrolyses indicates the catalytic properties of the modified conducting phase. The preparative electro-oxidation of investigated compounds showed that the 100% conversion of the substrate occurs in the shortest time on glassy carbon modified with Ce(III) ions immobilized in Nafion film. AFM tapping mode phase imaging was used to identify the hydrophobic and hydrophilic regions of Nafion perfluorosulfonate cation exchange membranes. The clusters agglomerates have a range of sizes from 5 to 30 nm.
- Domagala,Dziegiec,Cichomski,Grobelny
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p. 1049 - 1061
(2008/09/19)
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- Silica-gel-supported ceric ammonium nitrate (CAN): A simple and efficient solid-supported reagent for oxidation of oxygenated aromatic compounds to quinones
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A silica-gel-supported heterogeneous ceric ammonium nitrate (CAN) reagent has been developed for oxidizing oxygenated aromatics to quinones in nonaqueous media. The advantages of this procedure include excellent yields, mild reaction conditions, nonaqueous media, short reaction times, and easy product isolation. Copyright Taylor & Francis Group, LLC.
- Ali, Mohammed Hashmat,Niedbalski, Melinda,Bohnert, Gary,Bryant, Daniel
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p. 1751 - 1759
(2007/10/03)
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- The N-H and O-H bond dissociation energies in 4-hydroxydiphenylamine and its phenoxyl and aminyl radicals
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The N-H and O-H bond dissociation energies in 4-hydroxydiphenylamine Ph-NH-C6H4-OH (DNH= 353.4, DOH=339.3 kJ mol-1) and its semiquinone radicals DNH(Ph-NH-C 6H4-O.) = 273.6, DOH(Ph-N .-C6H4-OH) = 259.5 kJ mol-1 were first estimated using the parabolic model and experimental data (rate constants) on two elementary reactions with participation of N-phenyl-1,4- benzoquinonemonoimine (2). One of the reactions, namely, that of 2 with aromatic amines, was studied in this work using a specially developed method.
- Varlamov
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p. 306 - 312
(2007/10/03)
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- Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction
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A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method.
- Ling, Taotao,Poupon, Erwan,Rueden, Erik J.,Kim, Sun H.,Theodorakis, Emmanuel A.
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p. 12261 - 12267
(2007/10/03)
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- Hydroxylation of substituted diatomic phenols and their derivatives
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Oxidation of 3,6-di-tert-butylpyrocatechol in protic media is accompanied by the formation of 3,6-di-tert-butyl-2-hydroxy-para-benzoquinone. Hydroxylation of the 3,5-isomer results in dealkylation and isomerization with the formation of 6-tert-butyl-2-hydroxypora-benzoquinone and the quinone mentioned above, respectively. Their ratio depends on the nature of the solvent. Analogous processes accompany redox transformations of 2,6-di-tert-butylhydroquinone, 2,6-diphenyl-para-benzoquinone, and 2,4,6-tri-tert-butylphenol adsorbed on silica gel. Derivatives of 3,5-substituted pyrocatechols formed under conditions of heterophase oxidation in air are capable of transformations to form nitrogen-containing compounds.
- Vol'eva,Prokof'eva,Belostotskaya,Komissarova,Ershov
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p. 1952 - 1955
(2007/10/03)
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- Photochemical nitration by tetranitromethane. Part XXXV. A possible addition/elimination pathway in the photochemical reaction of 2,5-di-tert-butyl-1,4-dimethoxybenzene and tetranitromethane
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The photolysis of the charge transfer complex of 2,5-di-tert-butyl-1,4-dimethoxybenzene (1) and tetranitromethane gives exclusively 4-tert-butyl-2,5-dimethoxynitrobenzene (2) in both dichloromethane and acetonitrile at room temperature. Photolysis in dichloromethane in the presence of trifluoroacetic acid (0.10-1.0 mol dm-3), gives 2,5-di-tert-butyl-1,4-benzoquinone (3) (6-25%), 5-tert-butyl-4-methoxy-1,2-benzoquinone (4) (9-25%) and 5-tert-butyl-4-methoxy-1,2-dihydroxybenzene (5) (13-25%) together with 2 (25-71%). Nitration of 1 with HNO3/acetic anhydride or a solution of nitrogen dioxide in dichloromethane gives 2 as the main product, together with products 3-5. It is suggested that 2 is formed in the photolysis by the decomposition of transient adducts, in which trinitromethyl and NO2 have been added across the aromatic ring. The protonation of trinitromethanide by trifluoroacetic acid eliminates the nucleophile and thus inhibits the formation of adducts, and the products are then formed mainly by coupling of nitrogen dioxide with the radical cation 1?+ or 1. Acta Chemica Scandinavica 1997.
- Svensson, Jan Olof
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- PROCESS FOR PRODUCING QUINONES
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Provided is a process for preparing quinone in high purity, in high quality and in high yield in industrially easy manner and with no specific equipment and machinery and with no specific operations. In liquid phase, an aromatic diol compound is reacted with peroxide in the presence of a catalyst with a component I containing one or more elements selected from the group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium and rhenium.
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- Chemistry of Organo Halogenic Molecules. 140. Role of the Reagent Structure on the Transformations of Hydroxy Substituted Organic Molecules with the N-Fluoro Class of Fluorinating Reagents
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Hydroxy-substituted organic molecules were used as target molecules in investigations of the role of the reagent structure on the reactivity of three types of N-F class fluorinating reagents: 1-chloromethyl-4-fluoro-1,4-diazoniabicyclooctane bis(tetrafluoroborate) F-TEDA (1a), N-fluorobis(phenylsulfonyl)amine NSF (1b), and N-Fluoropyridinium heptafluorodiborate-pyridine (1/1) NFP (1c).Methanol is stable, but hydroquinone is very quickly transformed in acetonitrile to quinone with F-TEDA at room temperature: on the other hand, NSF is less reactive, while oxidation with NFP is achieved only at an elevated temperature; a structure variation of the hydroquinone derivatives did not influence oxidation.Fluorination was achieved with monohydroxy-substituted aromatic compounds; a similar trend concerning the reactivity of N-F reagent (1) was also observed in reactions with 1- and 2-naphthol, while 9-phenanthrol gave 10,10-difluoro-9-(10H)-phenanthrenone with F-TEDA in acetonitrile and 9,10-phenanthrenequinone with NSF.Dealkylation was observed in a reaction with 4-methoxyphenol; although the thio analogue gave bis(4-methoxyphenyl) disulfide, the reactivity was changed and NSF was more reactive than F-TEDA and NFP.
- Zupan, Marko,Iskra, Jernej,Stavber, Stojan
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p. 1655 - 1660
(2007/10/02)
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- Fe(III)-EDTA mediated autoxidation of 2,6-di-t-butylphenol and substituted hydroquinones by molecular oxygen
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Fe(III)-EDTA in aq. MeOH offers a simple environmentally acceptable synthetic tool to oxidize 2,6-di-t-butylphenol to 3,3',5,5'-tetra-t-butyl- 4,4'-diphenoquinone by molecular oxygen with 100% selectivity and several alkyl-substituted hydroquinones to their quinones, in excellent yields, under mild conditions.
- Sain, Bir,Murthy, Pappu S.,Venkateshwar Rao,Prasada Rao,Joshi, Girish C.
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p. 5083 - 5084
(2007/10/02)
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- Solid state redox chemistry of hydroquinones and quinones
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Solid state ceric ammonium nitrate (CAN) oxidation of hydroquinones to the corresponding quinones, gives best results when operating with ultrasonic irradiation. Nitrogen dioxide plays a key role in these 'solid-solid' oxidations. The oxidation of hydroquinones to quinones can also be achieved in a unique 'solid-solid-solid' reaction, i.e., by using a limited amount of CAN in the presence of a full equivalent of a solid cooxidant such as KBrO3. Reduction of quinones with sodium dithionite in the solid state gives rise to the corresponding highly colored quinhydrones and, eventually, to hydroquinones.
- Morey,Saa
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p. 105 - 112
(2007/10/02)
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- Oxidation Using Quaternary Ammonium Polyhalides. VIII. Oxidation of 1,4-Benzenediols with Benzyltrimethylammonium Tribromide
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The reaction of 1,4-benzenediols with 1.1 equiv of benzyltrimethylammonium tribromide in dichloromethane in the presence of aqueous sodium acetate at room temperature gave 2,5-cyclohexadiene-1,4-diones in good yields.On the other hand, the reaction of 1,4-benzenediols with a large excess of the reagent in aqueous acetic acid at 40-60 deg C gave polybromo-substituted 2,5-cyclohexadiene-1,4-diones in good yields.
- Kajigaeshi, Shoji,Morikawa, Yukihiro,Fujisaki, Shizuo,Kakinami, Takaaki,Nishihira, Keigo
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p. 336 - 338
(2007/10/02)
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- ROLE OF THE POLYMER BACKBONE IN THE OXIDATIVE PROPERTIES OF POLYMER - SUPPORTED DICHROMATE
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Crosslinked co/poly(styrene-4-vinylpyridine)/ (1) was converted with hydrogen bromide or alkyl bromide to a pyridinium salt (2) which was further converted in water medium to various immobilized dichromates (3) with CrO3.The insoluble reagent containing 0.6 -1.0 mmol of dichromate on a gram of resin (depending on the structure of the polymer backbone) oxidized several secondary alcohols to ketones.The rate of conversion of alcohols to ketones depended on the structure of the polymer backbone, the structure of the alcohol, and the amount of water (5percent or 20percent) occluded in the reagent 3.
- Zdravkovski, Zoran,Zupan, Marko
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p. 1317 - 1324
(2007/10/02)
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- Reactivity of some Quinones with Alkylaluminium Compounds
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The reactions of 2-methyl-1,4-naphthoquinone with triethylaluminium and 2,5-di-t-butyl-1,4-benzoquinone with triisobutylaluminium were studied.In each of these reactions three different products were obtained and characterized by n.m.r. and i.r.U.V. spectrophotometry showed that 2-methyl-1,4-naphthoquinone behaves as a weak base and the ionization constants pK1 = -0.922 and pK2 = -4.065 were reported in aqueous HClO4.This is a useful information for elucidating the mechanism of the first reaction studied, based on the different basicity of the carbonyl groups.
- Leal, J. M.,Arcos, J.,Garcia, B.
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p. 887 - 896
(2007/10/02)
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- TELLURAMINE DERIVATIVES AS SELECTIVE OXIDANTS
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Tetravalent morpholino-tellurium derivatives 1 and 6 quickly oxidize hydroquinones to quinones and thiols to disulphide under neutral conditions.Bulky phenol 15 is slowly oxidized by 5 and 6 to diphenoquinone 16.
- Barton, Derek H. R.,Finet, Jean-Pierre,Gianotti, Charles,Thomas, Martial
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p. 2671 - 2674
(2007/10/02)
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- PYRIDINE ASSISTED OXIDATIONS OF ALCOHOLS TO CARBONYL COMPOUNDS BY MEANS OF 3-CARBOXYPYRIDINIUM DICHROMATE (NDC) REAGENT.
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3-carboxypyridinium dichromate (NDC), readly prepareted from nicotinic acid and chromium trioxide, is an efficient reagent for the oxidation of alcohols into carbonyl compounds in the presence of pyridine.The optimum molar ratio substrate:reagent:pyridine to ensure complete oxidation of starting material in a short reaction time was found 1:2.5:20 respectlively.A brief compouison between this reagent and pyridinium dichromate (PDC) is made.In contrast to the PDC reagent, NDC allows selective oxidation between benzylic alcohols and aliphatic alcohols.The NDC-pyridine system has been successfully extended to the oxidation of N-(2-hidroxy-2-phenyl or 2-methylethyl)-β-lactams into their corresponding carbonyl compounds as N-H azetidin-2-one precursor.In contrast, primary N-(2-hydroxyethyl)-β-lactams upon treatment with this reagent system afforded N-formylazetidin-2-ones.The influence of pyridine in oxidations by means of NDC is further shown in the conversion of hydroquinones into quinones.Another interesting feature associated with the use of this reagent is the ease of purification of the final products.
- Cossio, Fernando P.,Lopez, Concepcion M.,Palomo, Claudio
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p. 3963 - 3974
(2007/10/02)
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- FUNCTIONAL GROUP OXIDATION USING SODIUM PERBORATE
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Sodium perborate in acetic acid is an effective reagent for the oxidation of anilines to nitroarenes and of sulphides to either sulphoxides or sulphones.It is also an excellent reagent for the oxidative deprotection of ketone dimethylhydrazones.Baeyer-Villiger oxidation of ketones can be carried out with sodium perborate in either trifluoroacetic acid or acetic acid/trifluoroacetic acid mixtures, and hydroquinones and certain highly substituted phenols are smoothly converted into quinones.
- McKillop, Alexander,Tarbin, Jonathan A.
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p. 1753 - 1758
(2007/10/02)
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- SYNTHETIC APPLICATIONS OF CHROMIUM(VI) REAGENTS IN COMBINATION WITH CHLOROTRIMETHYLSILANE
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The synthetic utility of chromium(VI) reagents together with chlorotrimethylsilane, as new oxidizing systems, is described.Pyridinium dichromate (PDC) in combination with chlorotrimethylsilane oxidizes tert-butyldimethylsilyl ethers in good to excellent yields.Trimethylsilyl chlorochromate, a new chromium(VI) reagent, also was found efficient for this oxidative-deprotection method.These reagents were applied to the oxidation of some N-(2-phenyl-2-hydroxyethyl)azetidin-2-ones as well as N-(2-phenyl-2-trialkylsiloxy)azetidin-2-ones into their corresponding carbonyl compounds, key intermediates for N-unsubstituted β-lactams.Oxidation of hydroquinones and protected trialkylsilyl hydroquinones was also described.Protection of hydroquinones by means of the tert-butyldimethylsilyl group was achieved by using the readily available tert-butyldimethylchlorosilane (TBDMCS) and 1,8-diazabicycloundec-7-ene (DBU) as base, which avoids the use of sophisticated and (or) sensitive reagents.
- Cossio, Fernando P.,Aizpurua, Jesus M.,Palomo, Claudio
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p. 225 - 231
(2007/10/02)
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- ORGANOTELLURINIC ACID ANHYDRIDES AS SELECTIVE OXIDANTS IN ORGANIC SYNTHESIS
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Several aryltellurinic acid anhydrides have been compared for their oxidising properties in acetic acid.Very high yields of quinones and disulphides can be obtained under conditions where phenols are not oxidised.
- Barton, Derek H. R.,Finet, Jean-Pierre,Thomas, Martial
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p. 2319 - 2324
(2007/10/02)
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- Polymer-supported Periodate and Iodate as Oxidizing Agents
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The periodate forms of some commercial macroporous anion-exchange resins can be used in either protic or aprotic solvents to oxidize various quinols, catechols, and glycols and also triphenylphosphine, hydrazobenzene, and benzohydroxamic acid.The reagents in methanol oxidize thioethers.Polymer-supported iodate also oxidizes quinols and catechols.
- Harrison, Charles R.,Hodge, Philip
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p. 509 - 511
(2007/10/02)
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- Pyridinium Chlorochromate Releases Quinones from Hydroquinone Silyl Ethers.
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The pyridinium chlorochromate oxidation of six bis(trimethylsilyl) and six bis(tert-butyldimethylsilyl) ethers of p-hydroquinones at room temperature in methylene chloride solution gave the corresponding quinones in 60-90percent yield.The bis(trimethylsilyl) ethers were slightly more reactive than the bis(tert-butyldimethylsilyl) ethers.High oxidation efficiency was indicated by a 1:1 molar stoichiometry; however, more convenient reaction times were obtained at a 2:1 molar ratio of pyridinium chlorochromate (PCC) to hydroquinone silyl ether.The mechanism is discussed based upon comparisons of relative reaction rates with electrochemical oxidation potentials.
- Willis, John P.,Gogins, Kitty A.,Miller, Larry L.
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p. 3215 - 3218
(2007/10/02)
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- FeCl3/SiO2 Reacts as Oxidant or Lewis Acid with Phenol Ethers
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Adsorption of FeCl3*6H2O onto silica gel produces a supported reagent FeCl3/SiO2.This reagent is insoluble in CH2Cl2 and is used in that solvent for reaction with phenol ethers.Dimethoxy aromatics are coupled to produce biaryls in high yield.Seven examples including both inter- and intramolecular couplings are reported.The effect of various support materials is explored.An electron-transfer mechanism is proposed.Disiloxy aromatics are oxidized to quinones.Ten examples of substituted 1,4-bis(trimethylsiloxy)- or 1,4-bis(tert-butyldimethylsilyloxy)benzene oxidations are reported.In one example the reaction is catalytic in FeCl3, being driven by oxygen.Benzyloxy aromatics are cleaved to phenols.In this reaction FeCl3 acts on a Lewis acid.The importance of coadsorbing the reagent and the aromatic ether in the absence of solvent is demonstrated.
- Jempty, Thomas C.,Gogins, Kitty A. Z.,Mazur, Yehuda,Miller, Larry L.
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p. 4545 - 4551
(2007/10/02)
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- Oxidation Reactions using Sodium Metaperiodate Supported on Silica Gel
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No reaction occurred when solutions of 2,5-di-t-butylhydroquinone, dibenzyl sulphide, trans-cyclohexane-1,2-diol or hydrazobenzene in methylene chloride were stirred with powdered sodium metaperiodate at 20 deg C for several hours.However, these and several closely related substrates were oxidized in good yield, generally within a few hours, when solutions in methylene chloride, and in some cases benzene or ether, were stirred with sodium metaperiodate supported on silica gel.The supported reagent was prepared by evaporating to dryness an aqueous solution of sodium metaperiodate in the presence of silica gel, followed by heating at 120 deg C in vacuo.The reagent appears to consist mainly of a monomolecular layer of sodium metaperiodate bound to the silica gel by the surface hydroxy-groups, together with a minor amount of crystalline anhydrous sodium metaperiodate.
- Gupta, Dharmendra N.,Hodge, Philip,Davies, J. Eric
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p. 2970 - 2973
(2007/10/02)
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- Oxidation of Hydroquinone Silyl Esters to Quinones
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The electrochemical oxidation of trialkylsiloxybenzene derivatives was investigated using platinum and graphite anodes in either acetonitrile or methylene chloride solvent.Preparative oxidation of the bis(trimethylsilyl) ethers of hydroquinone, chlorohydroquinone, 2,5-di-tert-butylhydroquinone, and 9,10-dihydroxyanthracene gave the corresponding quinones in 80-90percent yield.Oxidation of 1,4-bis(trimethylsiloxy)-2-methoxybenzene in acetonitrile gave 3,6-dihydroxy-2,7-dimethoxydibenzofuran in 65percent yield.Oxidation of 1-methoxy-4-(trimethylsiloxy)benzene in methanolic acetonitrile produced 1,1-dimethoxy-2,5-cyclohexadien-4-one in 99percent yield.The cyclic voltammograms of the trimethylsilyl, triethylsilyl, and tert-butyldimethylsilyl ethers of 2,5-di-tert-butylhydroquinone were recorded using acetonitrile and methylene chloride solvents at 25 and -60 deg C.These compounds were found to react by initial one-electron oxidation to generate a cation radical which decomposes by silicon-oxygen bond cleavage to eventually form quinone.The relative rates for decomposition of the trimethylsilyl, triethylsilyl, and tert-butyldimethylsilyl ether cation radicals at -60 deg C were 10:5:1. tert-Butyldimethylsilyl chloride and tert-butyldimethylsilyl triflate were found to be stable toward cathodic reduction in dry methylene chloride and acetonitrile at potentials as negative as -2.1 vs.Ag/0.1 M AgNO3.Cyclic voltammetry indicated that reduction of 2,5-di-tert-butylbenzoquinone, anthraquinone, and naphthoquinone in the presence of tert-butyldimethylsilyl chloride resulted in reductive silylation.
- Stewart, Ray F.,Miller, Larry L.
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p. 4999 - 5004
(2007/10/02)
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- Reactions of some substituted phenols with chromyl and vanadyl chlorides
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The oxidation of 2,4,6-tritertbutylphenol and several other alkyl and halophenols by CrO2Cl2 and VOCl3 was studied.The products of CrO2Cl2 oxidation are mostly quinones and diphenoquinones, whilst those of VOCl3 oxidation also include major amounts of dealkylated phenols and C-C coupled dimers.The product distributions are interpreted in terms of a mechanism involving phenoxyl radicals, ligand transfer from metal to radical, and either phenoxonium ions or metallate esters where there is sufficient electron withdrawal from the organic group for it to exhibit carbenium ion properties.The differences in behaviour between CrO2Cl2, VOCl3, and CuCl2 are attributed to different balances between the oxidation potential and Lewis acidity of the metal complexes.It is concluded that CrO2Cl2 is not a good model for proposed ferryl intermediate in heme oxidase systems since it induces 1 --> 3 rather than 1 --> 2 halogen shifts and an NIH shift that is best explained by carbenium ion-like intermediates.
- Harrod, John F.,Pathak, Asha
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p. 686 - 693
(2007/10/02)
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- Phosphorescence exhibiting materials for optically pumped lasers
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Chemical compounds resulting from the mixing of organosilanes and quinones in the presence of di-tert-butyl peroxide as a sensitizer, exhibit strong blue phosphorescence. These compounds are highly resistant to deterioration by heat and UV irradiation. The unique feature of enhanced phosphorescence quantum efficiency at high temperature makes these systems most suitable for solar pumped lasers which usually will operate at relatively high temperature.
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