- Estimation of kinetic parameters of reversible chain reactions of quinoneimines with hydroquinones having self-acceleration periods
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A new approach is suggested for determining the kinetic parameters and rate constants of the elementary steps of reversible chain reactions having self-acceleration periods due to the long time required for the concentrations of the chain-carrier radicals to reach their steady-state values. This approach is illustrated by the example of the reversible chain reaction between N,N′-diphenyl-1,4-benzoquinonediimine and 2,5-dichlorohydroquinone in chlorobenzene. The disappearance rate of one of the initial reactants, N,N′-diphenyl-1,4-benzoquinonediimine, at the inflection point of its disappearance curve, is considered as the basic kinetic characteristic of the reaction. The empirical function y = aexp(bt c ) + d, where a, b, c, and d are the fitted parameters (b 1), is suggested for approximating the S-shaped kinetic curves and for calculating the reaction rate. The rate constants of the elementary steps are preferably derived from experimental data obtained at equal concentrations of the initial reactants, and also product additions when their effect on the reaction rate is studied. The effective rate constant of chain termination is derived from the time to reach the steady state. The results obtained in this way are compared with earlier data obtained using the "initial" reaction rates calculated by means of exponential approximation of portions of N,N′-diphenyl-1,4- benzoquinonediimine disappearance curves after the inflection point.
- Varlamov,Gadomsky
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Read Online
- 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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- Reactivity of a Ru(iii)-hydroxo complex in substrate oxidation in water
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A mononuclear RuIII-OH complex oxidizes substrates such as hydroquinones in water through a pre-equilibrium process based on adduct formation by hydrogen bonding between the RuIII-OH complex and the substrates. The reaction mechanism switches from hydrogen atom transfer to electron transfer depending on the oxidation potential of substrates. This journal is
- Ohzu, Shingo,Ishizuka, Tomoya,Kotani, Hiroaki,Kojima, Takahiko
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supporting information
p. 15018 - 15021
(2015/02/19)
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- The use of sodium chlorate/hydrochloric acid mixtures as a novel and selective chlorination agent
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Sodium chlorate/hydrochloric acid mixtures were used to chlorinate activated arenes and the α-position of ketones. This chlorination method was used to produce selectively mono-, di-, and trichlorinated compounds by controlling the molarity of sodium chlorate. This reagent proved to be much more efficient and easier to handle than chlorine gas.
- Moon, Byung Seok,Choi, Han Young,Koh, Hun Yeong,Chi, Dae Yoon
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experimental part
p. 472 - 476
(2011/12/04)
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- Characterization of chlorophenol 4-monooxygenase (TftD) and NADH:FAD oxidoreductase (TftC) of burkholderia cepacia AC1100
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Burkholderia cepacia AC1100 completely degrades 2,4,5-trichlorophenol, in which an FADH2-dependent monooxygenase (TftD) and an NADH:FAD oxidoreductase (TftC) catalyze the initial steps. TftD oxidizes 2,4,5-trichlorophenol (2,4,5-TCP) to 2,5-dichloro-p-benzoquinone, which is chemically reduced to 2,5-dichloro-p-hydroquinone (2,5-DiCHQ). Then, TftD oxidizes the latter to 5-chloro-2-hydroxy-p-benzoquinone. In those processes, TftC provides all the required FADH2. We have determined the crystal structures of dimeric TftC and tetrameric TftD at 2.0 and 2.5 A resolution, respectively. The structure of TftC was similar to those of related flavin reductases. The stacked nicotinamide:isoalloxazine rings in TftC and sequential reaction kinetics suggest that the reduced FAD leaves TftC after NADH oxidation. The structure of TftD was also similar to the known structures of FADH2-dependent monooxygenases. Its His-289 residue in the re-side of the isoalloxazine ring is within hydrogen bonding distance with a hydroxyl group of 2,5-Di-CHQ.AnH289Amutation resulted in the complete loss of activity toward 2,5-DiCHQ and a significant decrease in catalytic efficiency toward 2,4,5-TCP. Thus, His-289 plays different roles in the catalysis of 2,4,5-TCP and 2,5-DiCHQ. The results support that free FADH2 is generated by TftC, and TftD uses FADH2 to separately transform 2,4,5-TCP and 2,5-DiCHQ. Additional experimental data also support the diffusion of FADH2 between TftC and TftD without direct physical interaction between the two enzymes.
- Webb, Brian N.,Ballinger, Jordan W.,Kim, Eunjung,Belchik, Sara M.,Lam, Ka-Sum,Youn, Buhyun,Nissen, Mark S.,Xun, Luying,Kang, Chulhee
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scheme or table
p. 2014 - 2027
(2011/02/22)
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- Synthesis of 2,5-Diaminoquinones by one-pot copper-catalyzed aerobic oxidation of hydroquinones and addition reaction of amines
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The aerobic oxidation of various hydroquinones was achieved by using copper nanoparticles entrapped in aluminum oxyhydroxide [Cu/ AlO(OH)] at room temperature. Furthermore, 2,5diamino-1,4-benzoquinones were synthesized directly from hydroquinone and amines by a one-pot procedure consisting of the copper-catalyzed aerobic oxidation of hydroquinones and the double addition of amines to the resulting quinones.
- Kim, Sungjin,Kim, Daehwan,Park, Jaiwook
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experimental part
p. 2573 - 2578
(2009/12/29)
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- Aerobic oxidation of hydroquinone derivatives catalyzed by polymer-incarcerated platinum catalyst
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(Chemical Equation Presented) It's a lock-in! A remarkably wide substrate scope of hydroquinones are oxidized to quinones in high yields in a platinum-catalyzed process with as low as 0.05 mol% catalyst. The aerobic oxidation is catalyzed by platinum nanoclusters trapped in a styrene-based polymer network (see scheme, PI Pt=polymer-incarcerated nanoclusters). The catalyst could be reused at least 13 times without any loss of catalytic activity.
- Miyamura, Hiroyuki,Shiramizu, Mika,Matsubara, Ryosuke,Kobayashi, Shu
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supporting information; experimental part
p. 8093 - 8095
(2009/04/13)
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- Rate constants of elementary steps of the reversible chain reaction of N-phenyl-1,4-benzoquinonemonoimine with 2,5-dichlorohydroquinone
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The kinetics of reversible chain reactions in quinoneimine-hydroquinone systems has first been studied for the reaction of N-phenyl-1,4- benzoquinonemonoimine with 2,5-dichloro-hydroquinone used as an example. The dependences of the reaction rate on the concentration of the initial reactants, initiator, and each product were studied. The reliable estimates of the rate constants of 11 (of 12) elementary steps of this reaction were obtained from the experimental data using the earlier derived formulas and the method of equal concentrations developed in the present work.
- Antonov,Varlamov
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p. 883 - 889
(2008/09/18)
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- Solvent effect on the equilibrium constant of the chain reversible reaction of N,N'-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone
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The temperature dependences of the equilibrium constant K of the reversible chain reaction of N,N'-diphenyl-1,4-benzoquinonediimine with 2,5-dichlorohydroquinone in benzene, chlorobenzene, anisole, benzonitrile, and CCl4 were studied. The enthalpies and entropies of the reaction in these solvents were determined, and a linear dependence between them in aromatic solvents was found. The equilibrium constant depends on the solvent nature: the replacement of CCl4 by benzene at T = 298 K increases K from 13.6 to 140. The solvation effects are caused by several types of intermolecular interactions of participants of equilibrium with the medium. The decrease in K in the benzene-anisole-benzonitrile series is related, to a great extent, to complex formation with hydrogen bonding between 2,5-dichlorohydroquinone and the solvents. In anisole a charge-transfer complex is formed between the solvent and reaction product (2,5-dichloroquinone). The constant and enthalpy of the complexation were estimated.
- Gadomsky,Varlamov
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body text
p. 2376 - 2383
(2009/02/05)
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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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- Determination of dissociation energies of N-H bond in the 4-anilinodiphenylaminyl radical and O-H bond in the 2,5-dichloro-4- hydroxyphenoxyl radical from the equilibrium constants of chain reactions in quinoneimine-hydroquinone systems
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The temperature dependences of the equilibrium constants of two chain reversible reactions in quinonediimine (quinonemonoimine)-2,5- dichlorohydroquinone systems in chlorobenzene were studied. The enthalpy of equilibrium of the reversible reaction of quinonediimine with 4-hydroxydiphenylamine was estimated from these data (ΔH = - 14.4±1.6 kJ mol-1) and a more accurate value of the N-H bond dissociation energy in the 4-anilinodiphenylaminyl radical was determined (DNH = 278.6±3.0 kJ mol-1). A chain mechanism was proposed for the reaction between quinonediimine and 2,5-dichlorohydroquinone, and the chain length was estimated (ν = 300 units) at room temperature. Processing of published data on the rate constant of the reaction of styrylperoxy radicals with 2,5-dichlorohydroquinone in the framework of the intersecting parabolas method gave the O-H bond dissociation energy in 2,5-dichlorohydroquinone: DOH = 362.4±0.9 kJ mol-1. Taking into account these data, the O-H bond dissociation energy in the 2,5-dichlorosemiquinone radical was found: DOH = 253.6±1.9 kJ mol-1.
- Antonov,Gadomsky,Varlamov
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p. 1723 - 1728
(2008/02/09)
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- A kinetic study of the early steps in the oxidation of chlorophenols by hydrogen peroxide catalyzed by a water-soluble iron(III) porphyrin
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The kinetics and mechanism of the initial steps in the oxidation of 2,4,6-trichlorophenol by hydrogen peroxide using iron(III) meso-tetra(4- sulfonatophenyl)porphine chloride as a catalyst were studied in this work. The first oxidation step is the formation of a substituted 1,4-benzoquinone. This step was also studied using a selection of differently substituted chlorophenols. It was shown that the rate constants characteristic for the oxidation of the substrate do not follow the pattern of pKaS, but correlate well with the 13C chemical shifts of the carbon atoms directly bonded to the oxygen in chlorophenols. The kinetics of the catalyzed and uncatalyzed oxidation of 2,6-dichloro-1,4-benzoquinone by hydrogen peroxide was also studied. The catalyzed and uncatalyzed pathways give different products.
- Lente, Gabor,Espenson, James H.
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p. 847 - 852
(2007/10/03)
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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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- Efficient, multigram-scale synthesis of three 2,5-dihalobenzoquiones
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2,5-Dibromo-, 2,5-dichloro- and 2,5-diiodobenzoquinone were conveniently prepared from 1,4-dimethoxybenzene in 87%, 97% and 84% overall yields. None of the two steps of the synthesis required purification.
- Lopez-Alvarado, Pilar,Avendano, Carmen,Menendez, J. Carlos
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p. 3233 - 3239
(2007/10/03)
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- Photoinduced electron transfer between acenaphthylene and 1,4-benzoquinones. Formation of dimers of acenaphthylene and 1 : 1-adducts and effect of excitation mode on reactivity of the charge-transfer complexes
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Photochemical reactions of acenaphthylene (ACN) with 1,4-benzoquinones (BQs) of varying reduction potentials in solution have been investigated in order to determine final products and quantum yields of the reactions and to get an insight into the factors
- Haga, Naoki,Takayanagi, Hiroaki,Tokumaru, Katsumi
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p. 734 - 745
(2007/10/03)
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- Photochemical behaviour of 1,4-dichlorobenzene in aqueous solution
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Several photoproducts were identified in the direct photolysis of 1,4-dichlorobenzene (1,4-DCB) in air-saturated aqueous solution, namely 4-chlorophenol, hydroquinone, hydroxybenzoquinone, and 2,5-dichlorophenol. In the absence of oxygen the latter is not formed and phenol was detected, but the unexpected formations of 4,4′-dichlorobiphenyl, 2,4′,5-trichlorobiphenyl, and a terphenyl derivative are observed. Mechanisms are proposed to explain the formations of identified photoproducts. The phototransformation of 1,4-DCB may be photoinduced by NO3- or FeIII salts. The main primary product is 2,5-dichlorophenol, which results from a hydroxylation without dechlorination. Some other products have been identified in particular 4-chlorophenol and 2,5-dichlorobenzoquinone in the case of FeIII salts.
- Meunier,Pilichowski,Boule
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p. 1179 - 1186
(2007/10/03)
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- Competitive decay pathways of the radical ions formed by photoinduced electron transfer between quinones and 4,4′-dimethoxydiphenylmethane in acetonitrile
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The reactivity of the cation radical of (4-MeOC6H4)2CH2 photosensitized by 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl2BQ), and tetrachloro-1,4-benzoquinone (chloranil, CA) was investigated in acetonitrile. The main photoreaction products obtained by steady-state irradiation were identified to be: (4-MeOC6H4)2CHOC6H4OH, sensitized by BQ; (4MeOC6H4)2CHCl, sensitized by Cl2BQ; (4-MeOC6H4)2CHOH, sensitized by CA. The mechanism of their formation was investigated by nanosecond laser flash photolysis that allowed transient species (radical ions, neutral radicals, and ions) to be detected and characterized in terms of absorption spectra, formation quantum yields, and decay rate constants. For all systems, the interaction between the triplet quinone (Q) and (4-MeOC6H4)2CH2 produced the corresponding radical ions (quantum yield φ ≥ 0.72) which mainly decay by back electron transfer processes. Less efficient reaction routes for the radical ions Q.- and (4-MeOC6H4)2CH2.+ were also: i) the proton-transfer process with the formation of the radical (4MeOC6H4)2CH. by use of Cl2BQ; ii) the hydrogen-transfer process with the formation of the cation (4-MeOC6H4)2CH+ in the case of CA. Instead, BQ sensitized a much higher yield of BQH. and (4MeOC6H4)2CH., mainly by the direct interaction of triplet BQ with (4MeOC6H4)2CH2. It was also shown that the presence of salts decreases significantly the rate of the back electron transfer process and enhances the quantum yields of formation of the neutral radicals and ions when Cl2BQ and CA are used, respectively. The behavior of BQ.-, Cl2BQ.-, and CA.- appears to be mainly determined by the Mulliken charges on the oxygen atom obtained from quantum mechanical calculations with the model B3LYP/6-311G(d,p). Spin densities seem to be much less important.
- Del Giacco, Tiziana,Baciocchi, Enrico,Lanzalunga, Osvaldo,Elisei, Fausto
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p. 3005 - 3013
(2007/10/03)
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- The kinetics and thermodynamics of quinone-semiquinone-hydroquinone systems under physiological conditions
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The steady-state concentration of semiquinones (Q·-) determined by EPR in the mixtures of eleven alkyl-, methoxy-and chloro-substituted 1,4-benzoquinones as well as 1,4-naphthoquinone (Q) with corresponding hydroquinones (QH2) in aqueous buffer. pH 7.40, was used to calculate a constant for equilibrium (1) Q + QH2?Q·- + Q·- + 2H+ (k1; 2k-1; K1 = k1/2k-1). The rale constants for comproportionation between Q and QH2, k1, were calculated from the combination of K1 determined in this work and 2k-1 reported previously. The Nernst equation was applied to calculate the change in one-electron reduction potential ΔE1 = E(Q/Q·-) - E(Q·-/QH2) in equilibrium (1). The E(Q·-/QH2) values were calculated from ΔE1 and the values of E(Q/Q·-) known from the literature. The correlations between E(Q·-/QH2) and E(Q/Q·-) as well as between ΔE1 (k1) and E(Q/Q·-) are discussed. The values of ΔE1 and k1 are suggested to be the key factors governing the autoxidation of QH2.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa
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p. 871 - 876
(2007/10/03)
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- Convenient preparations of the three 2,3-dihalo-1,4-benzoquinones
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Efficient preparations of 2,3-dichloro-1,4-benzoquinone (1) and 2,3- dibromo-1,4-benzoquinone (2) from 1,4-benzoquinone are reported, as is the synthesis of the previously unknown 2,3-diiodo-1,4-benzoquinone (3) from 2.
- Yu, Duyi,Mattern, Daniell Lewis
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p. 821 - 825
(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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- Chlorination of quinonoid compounds using dichlorine monoxide
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Dichlorine monoxide is a selective reagent for the monochlorination at the active quinonoid position in benzoquinones and naphthoquinones.
- Thapliyal,Singh,Khanna
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p. 1079 - 1083
(2007/10/02)
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- Selective halogenation of 1,4-benzoquinones and 1,4-naphthoquinones with copper(II) halide adsorbed on alumina
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1,4-Benzoquinone or 1,4-naphthoquinone and their derivatives have been halogenated selectively at quinonoid positions with copper(II) halide adsorbed on neutral alumina followed by refluxing in halobenzene to give mono-, di-, tri- and tetra-haloquinones.
- Singh,Khanna
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p. 2083 - 2089
(2007/10/02)
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- Energetic Comparison between Photoinduced Electron-Transfer Reactions from NADH Model Compounds to Organic and Inorganic Oxidants and Hydride-Transfer Reactions from NADH Model Compounds to p-Benzoquinone Derivatives
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Kinetics studies on photoinduced electron-transfer reactions from dihydropyridine compounds (PyH2) as being NADH model compounds to organic and inorganic oxidants and hydride-transfer reactions from PyH2 to p-benzoquinone derivatives (Q) in the absence and presence of Mg2+ ion are reported by determining over 150 rate constants.These results, combined with the values of Gibbs energy change of the photoinduced electron-transfer reactions as well as those of each step of the hydride-transfer reactions as being the e--H+-e- sequence, which are determined independently, revealed that the rate constants of the photoinduced electron-transfer reactions obey the Rehm-Weller-Gibbs energy relationship and that the activation barrier of the hydride-transfer reactions from PyH2 to Q is dependent solely on the Gibbs energy changes of the initial electron transfer from PyH2 to Q and the following proton transfer from PyH2.+ to Q.- and thus independent of the Gibbs energy change of the final electron transfer from PyH. to QH..The retarding effect of Mg2+ ion observed on the photoinduced electron transfer and hydride-transfer reactions of PyH2 is ascribed to the positive shifts of the redox potentials of the ground and excited states of PyH2 due to the complex formation with Mg2+ ion.
- Fukuzumi, Shunichi,Koumitsu, Shintaro,Hironaka, Katsuhiko,Tanaka, Toshio
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p. 305 - 316
(2007/10/02)
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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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- 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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- The Reaction of Antimony(V) Chloride with p-Benzoquinone
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The reaction of p-benzoquinone with an excess of SbCl5 gives 2,3,5,6-tetrachloro-p-benzoquinone ("Chloranil") in high purity and almost quantitative yield. 2,6- and 2,5-dichloro-p-benzoquinone could be identified as intermediate products. - Keywords: p-Benzoquinone, Antimony(V) Chloride
- Rettig, G.,Latscha, H. P.
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p. 399 - 400
(2007/10/02)
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