- Metal-free reduction of unsaturated carbonyls, quinones, and pyridinium salts with tetrahydroxydiboron/water
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A series of unsaturated carbonyls, quinones, and pyridinium salts have been effectively reduced to the corresponding saturated carbonyls, dihydroxybenzenes, and hydropyridines in moderate to high yields with tetrahydroxydiboron/water as a mild, convenient, and metal-free reduction system. Deuterium-labeling experiments have revealed this protocol to be an exclusive transfer hydrogenation process from water. This journal is
- Li, Tiejun,Peng, Henian,Tang, Wenjun,Tian, Duanshuai,Xu, Guangqing,Yang, He
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p. 4327 - 4337
(2021/05/31)
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- A dinuclear iron(II) complex bearing multidentate pyridinyl ligand: Synthesis, characterization and its catalysis on the hydroxylation of aromatic compounds
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A dinuclear iron(II) complex Fe2L2(μ2-Cl)2Cl2 (L = N,N-bis(pyridin-2-ylmethyl)prop-2-yn-1-amine) was prepared and fully characterized by UV–Vis spectroscopy, elemental analysis, electrochemical analysis and X-ray single crystal diffraction analysis. The catalytic activity of the complex was assessed for the hydroxylation of aromatic compounds by using aqueous H2O2 as an oxidant in acetonitrile. The catalytic system was applicable in a wide range of substrates including aromatic compounds with both electron-donating and electron-withdrawing substituents and showed moderate to good catalytic activity and selectivity in the oxidation reactions. Particularly, in the case of benzene the selectivity of phenol achieve to 74% with the reaction conversion of 24.8%.
- Gu, Erxing,Zhong, Wei,Ma, Hongxia,Xu, Beibei,Wang, Hailong,Liu, Xiaoming
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p. 159 - 165
(2018/03/29)
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- Oxidative coupling and hydroxylation of phenol over transition metal and acidic zeolites: Insights into catalyst function
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Reaction of phenol with hydrogen peroxide over H-MFI, Fe-MFI, H-BEA, Fe-BEA and TS-1 zeolite catalysts was investigated. Over H-BEA, biphenyl product was observed. It is suggested, that the larger pore size of H-BEA facilitates coupling of two phenol molecules. Two distinct reaction mechanisms are proposed for acid and redox catalysts.
- Li, Jerry Pui Ho,Kennedy, Eric,Stockenhuber, Michael
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- Reversible formation of aryloxenium ions from the corresponding quinols under acidic conditions
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Quinols, 1, are products of the hydration of O-aryloxenium ions, 2, and N-arylnitrenium ions, 3, and they are being investigated for medical uses. Under acidic conditions (pH 1-3) kinetics and products of Br- trapping demonstrate that 1a, 4-phenyl-4-hydroxy-2,5-cyclohexadienone, and 1b, 4-p-tolyl-4-hydroxy-2,5-cyclohexadienone, generate the corresponding oxenium ions 2a and 2b, respectively, as steady-state intermediates. Formation and trapping of the oxenium ions occurs in competition with the acid catalyzed dienone-phenol rearrangement. Because oxenium ion formation is reversible, the ion can only be detected by trapping with a nucleophile. Br- is an efficient trap under acidic conditions because, unlike N3 -, it is not protonated under those conditions. Attempts to detect the oxenium ions 2a and 2b at pH 4.6 and 7.1 with N3- were unsuccessful indicating that oxenium ion formation only occurs under acidic conditions. The oxenium ion 2c could not be detected under acidic conditions from the quinol 1c, 4-(benzothiazol-2-yl)-4-hydroxy-2,5-cyclohexadienone, by Br- trapping methods, even though this ion can be detected during hydrolysis of the corresponding ester, 4c. Although the benzothiazol-2-yl group is a resonance electron donor that is capable of stabilizing an O-aryloxenium ion, it is also a strong inductive electron withdrawing group that hinders the formation of 2c from 1c by decreasing the extent of protonation of 1c to generate 1cH+ and by destabilizing the transition state for ionization of 1cH+. Generation of an oxenium ion from the corresponding quinol is feasible under acidic conditions as long as the 4-substituent of the quinol is both a resonance and inductive electron donor. Copyright
- Chakraborty, Mrinal,Brzozowski, Christopher F.,Novak, Michael
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p. 1236 - 1242
(2013/08/24)
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- A direct approach to 5-hydroxybenzofurans via a platinum-catalyzed domino rearrangement/5-endo-dig cyclization reaction of quinols
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(Chemical Equation Presented) A highly efficient and atom-economical construction of 2-substituted 5-hydroxybenzofurans was accomplished by employing a platinum-catalyzed domino dienone-phenol rearrangement/5-endo-dig cyclization reaction of quinols beari
- Kim, Ikyon,Kim, Kyungsun,Choi, Jungeun
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scheme or table
p. 8492 - 8495
(2010/03/01)
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- Simple, mild, and efficient method for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN3
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A simple, mild, and efficient method is presented for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN3 under neutral conditions in the presence of water. Copyright Taylor & Francis Group, LLC.
- Algi, Fatih,Balci, Metin
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p. 2293 - 2297
(2007/10/03)
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- Synthesis of hydroxybiphenyls
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Cyclohexylphenols were converted into hydroxybiphenyls via dehydration over large-scale palladium catalysts. The process involves slow reaction of the substrate with active centers of the catalyst with subsequent fast product formation and hydrogen desorption.
- Kuznetsova,Postnova,Koshel',Lebedeva,Yun'kova,Koshel'
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p. 1288 - 1290
(2007/10/03)
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- One step hair coloring compositions using salts
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A hair coloring composition comprising the following two compositions which are mixed just prior to application to the hair: (a) a composition comprising a water-soluble peroxygen oxidizing agent; and (b) a composition comprising one or more oxidative hair coloring agents selected from the group consisting of an aromatic diamine, an amino phenol, a naphthol, a polyhydric phenol, a catechol and mixtures thereof; wherein the composition comprising one or more oxidative hair coloring agents further comprises al least one water soluble carbonate releasing salts; and optionally a water soluble ammonium salt, is described.
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- Photoreduction of p-Benzoquinones: Effects of Alcohols and Amines on the Intermediates and Reactivities in Solution
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The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (.QH/Q.-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, λirr = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the .QH/Q.- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.
- Goerner, Helmut
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p. 440 - 448
(2007/10/03)
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- Transition metal complexes as dye forming catalysts in hair coloring compositions
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A hair coloring composition comprising a first composition which comprises: (a) a dye forming transition metal salt or complex; which is first applied to the hair; and a second composition which comprises the following two compositions which are mixed just prior to application to the hair: (a) a composition comprising a water-soluble peroxygen oxidizing agent; and (b) a composition comprising one or more oxidative hair coloring agents selected from the group consisting of an aromatic diamine, an aminophenol, a polyhydric phenol a catechol and mixtures thereof.
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- Enhanced color deposition for hair with sequestering agents
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Hair coloring compositions which comprise: (A) non-nitrogenous chelating agents from the group consisting of polyphosphate; phosphonates; hydroxycarboxylates; polyacrylates; zeolite; and mixtures thereof; (B) an oxidative dye primary intermediate; and (C) an oxidative dye coupler; (D) and water are described. The present invention also relates to a method for coloring hair which comprises contacting said hair with a hair coloring composition as described above.
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- Novel access to cyclohexane-1,4-diones and 1,4-hydroquinones via radical 1,2-acyl rearrangement on 2-(halomethyl)cyclopentane-1,3-diones using cobaloxime-mediated electroreduction or tributyltin hydride
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A new preparative access to synthetically useful cyclohexane-1,4-diones 2 and their oxidized analogues, hydroquinones 3, with the option of introducing alkyl and aryl substituents, was developed by radical 1,2-acyl rearrangement on 2-(halomethyl)cyclopentane-1,3-diones 1, accessible from 1,2-bis(trimethylsiloxy)cyclobutene and α-bromo ketone dimethyl acetals. The electroreduction of monoacetals of 1 in the presence of cobaloxime as a catalyst afforded the cyclohexane-1,4-dione monoacetals in good yields. The Bu3SnH-reduction of 2-aryl 1 under refluxing in benzene effected the rearrangement, affording 2, and when the reaction was prolonged, aromatization to 3 proceeded in moderate yields.
- Kawafuchi, Hiroyuki,Inokuchi, Tsutomu
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p. 2051 - 2054
(2007/10/03)
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- Polymer electrolyte and process for producing the same
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A polymer electrolyte having, in a main chain, a structural unit represented by the following formula (1):-[Ar1-(SO2-N-(X+)-SO2-Ar2)m-SO2-N-(X+)-SO2-Ar1-O]- wherein Ar1 and Ar2 independently represent a divalent aromatic groups, m represents an integer of 0 to 3, and X+ represents an ion selected from hydrogen ion, an alkali metal ion and ammonium ion, which is excellent in proton conductivity, thermal resistance and strength. The polymer electrolyte is soluble in solvents and has excellent film forming property and recycling efficiency.
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- Metabolic activation of o-phenylphenol to a major cytotoxic metabolite, phenylhydroquinone: Role of human CYP1A2 and rat CYP2C11/CYP2E1
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1. The in vitro metabolic activation of o-phenylphenol has been evaluated as yielding a toxic metabolite, 2,5-dihydroxybiphenyl (phenylhydroquinone), by p-hydroxylation in liver microsomes of rat and human. The involvement of rat CYP2C11, CYP2E1 and human CYP1A2 in the p-hydroxylation of o-phenylphenol is suggested. 2. 2,3- and phenylhydroquinone, which induced DNA single-strand scission in the presence of 1 μM CuCl2, were the most cytotoxic chemicals examined to cultured mammalian cell lines among o-phenylphenol, m-phenylphenol, p-phenylphenol, 2,2'-, 4,4'-, 2,3- and phenylhydroquinone. 3. Rat and human liver microsomes catalysed the formation of phenylhydroquinone, but not 2,3-dihydroxybiphenyl, using o-phenylphenol as a substrate. A higher rate of metabolic activation of o-phenylphenol was observed with livers of the male than the female rats by 5.6- and 2.6-fold respectively. 4. Inhibitory antibodies against the male-specific CYP2C11 inhibited hepatic o-phenylphenol p-hydroxylation in the male F344 and Sprague-Dawley rat by > 70 %. Liver microsomes from the isoniazid-treated rats produced 1.8- and 3-fold induction of o-phenylphenol p-hydroxylation and chlorzoxazone 6-hydroxylation (a CYP2E1-dependent activity) respectively. 5. Human CYP1A2, expressed by baculovirus-mediated cDNA expression systems, exhibited a remarkably higher capacity for o-phenylphenol p-hydroxylation at concentrations of 5 (> 5-fold), 50 (> 2-fold) and 500 μM (> 2-fold) than CYP2A, CYP2B, CYP2Cs, CYP2D6, CYP2E1 and CYP3A4 on the basis of pmol P450. 6. Among various CYP inhibitors tested here, 7,8-benzoflavone and furafylline, typical human CYP1A2 inhibitors, inhibited the microsomal p-hydroxylation of o-phenylphenol in human livers most potently by 70 and 50 % respectively. 7. The results thus indicate the involvement of rat CYP2C11/CYP2E1 and human CYP1A2 in the hepatic p-hydroxylation of o-phenylphenol.
- Ohno,Ozawa,Ohta,Miyajima,Kurebayashi,Sunouchi,Shimizy,Murayama,Matsumoto,Fukuoka
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p. 1005 - 1017
(2007/10/03)
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- Redox reactions of phenylhydroquinone with quinones in water
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The reversible reaction of hydrogen transfer between phenylhydroquinone and quinones (p-benzo-quinone, chlorobenzoquinone, and methylbenzoquinone) was studied as depending on water pH and composition and the procedure for water pretreatment. A spectrophotometric technique for measuring low concentrations of phenylbenzoquinone produced in the reaction was developed, and the rate constants for the forward and back reactions and the equilibrium constants were calculated. The reaction rate increased drastically (by more than 4 orders of magnitude) as pH grew from 4 to 8. The dependence of the reaction rate in water on pH was explained by the formation of hydroquinone anions in the alkaline region. These anions are strong electron donors and readily react with quinone molecules. The mechanism of the redox reaction in the hydroquinone-p-benzoquinone system is considered in quantum-chemical terms.
- Kalnin'sh,Pavlova
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p. 1596 - 1600
(2007/10/03)
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- Mechanisms of the photochemical rearrangement of diphenyl ethers
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The mechanism of the photochemical rearrangement of diphenyl ether (1a) was studied. Irradiation of 1a in ethanol gave 2-phenylphenol (2, 42%) and 4-phenylphenol (3, 11%) as rearrangement products, in addition to phenol (4, 30%) and benzene (5, 25%) as diffusion products. Cross-coupling experiments employing [2H10]1a demonstrated that the formation of 2- and 4-phenylphenol was an intramolecular process. Irradiation of 1a in benzene or in toluene gave biphenyls in good yields. The combined yields of rearrangement products (2 and 3) increased with increase of solvent viscosity, with a concomitant decrease in the formation of 4. All the results can be rationalized in terms of excitation of 1a to the singlet state and dissociation to a radical pair intermediate involving phenoxy and phenyl radicals. Intramolecular recombination of these radicals gives rearrangement products, and escape followed by hydrogen abstraction from the solvent gives diffusion products. When position 4 of 1a was occupied by an electron-donating substituent (1b-e), aryloxy-phenyl bond cleavage to give the corresponding rearrangement products prevailed over phenoxy-aryl bond cleavage. The opposite was the case for substrates with an electron-withdrawing substituent at position 4 (1h,i).
- Haga, Naoki,Takayanagi, Hiroaki
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p. 735 - 745
(2007/10/03)
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- Acid-catalyzed rearrangement of O-(2-arylphenyl)hydroxylamines to aryldihydroazepinones
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Acid-catalyzed rearrangement of O-(2-arylpheynl) hydroxylamines followed by ring enlargement afford 7-aryl-2, 3-dihydro-1H-azepin-2-ones. 2-Amino-2-phenyl-3, 5-cyclohexadienone, an intermediate of the reaction, was trapped as the N-trifluoroacetamide.
- Endo, Yasuyuki,Kataoka, Ken-Ichiro,Haga, Naoki,Shudo, Koichi
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p. 3339 - 3342
(2007/10/02)
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- 1,3-Dipolar Cycloaddition Reactions of 1,4-Benzoquinones with Nitrilimines
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The cycloaddition reactions of some aryl conjugated p-benzoquinones with nitrilimines were studied.Depending upon the reaction conditions mono- and/or bis- adducts were isolated only from carbon-carbon double bond.The structure determination was unequivocally established by an X-ray analysis carried out on a bis-adduct.The observed regio-, as well as site-selectivity was qualitatively correlated with frontier molecular orbitals of the reacting species.
- Argyropoulos, N. G.,Mentzafos, D.,Terzis, A.
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p. 1983 - 1988
(2007/10/02)
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- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
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The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
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p. 479 - 485
(2007/10/02)
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- REACTIONS OF ORGANOLITHIUM REAGENTS WITH p-BENZOQUINONES AND CYCLOHEXADIENONS, SYNTHESIS OF 4-ALKYL-4-HYDROXYCYCLOHEXA-2,5-DIEN-1-ONES AND 1,4-DIALKYLCYCLOHEXA-2,5-DIENE-1,4-DIOLS.
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Addition of organolithium reagents to p-benzoquinones in ether gives the corresponding 4-alkyl-4-hydroxycyclohexa-2,5-dien-1-ones.Addition of excess of the reagent to the p-benzoquinones, or to the 4-alkyl-4-hydroxycyclohexa-3,5-dien-1-ones, in tetrahydrofuran, gives the corresponding dialkylcyclohexa-2,5-diene-1,4-diols.
- Fischer, A.,Henderson, N.
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p. 701 - 704
(2007/10/02)
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- Enzyme-activated oxidative process for coloring hair
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An enzyme-based oxidative process for coloring hair wherein the hair is exposed to a solution having a pH of about 4 to about 10 and containing hydrogen peroxide, soybean peroxidase enzyme and one or more oxidation dye precursors.
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