- Mobilities of Radical Cations and Anions, Dimer Radical Anions, and Relative Electron Affinities by Times of Flight in n-Hexane
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The mobilities of several radical cations and anions are measured in n-hexane using a thin-sheet time-of-flight (TOF) technique.We observe the radical cations of N,N,N',N'-tetramethyl-p-phenylenediamine, zinc tetraphenylporphine, and pyrene and the radical anions of perfluorobenzene, p-benzoquinone, anthraquinone, chloranil, buckminsterfullerene (C60), and octafluoronaphthalene.For all electron acceptors but C60, the dependence of the anionic TOF on acceptor concentration reveals the appearance of the homodimer radical anion at sufficiently high concentrations.The equilibrium constant for the monomer anion/monomer acceptor association reaction is obtained from the concentration studies.A Born-Haber cycle is then applied to estimate the difference between the electron affinities of the monomer and dimer molecules in the gas phase.
- Lim, S. K.,Burba, M. E.,Albrecht, A. C.
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- A Fast Kinetic Study of the Formation and Decay of N,N,N',N'-Tetramethyl-p-phenylenediamine Radical Cation in Aqueous Solution
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The oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) by S2O82-, HSO5-, H2O2, MnO4-, Cr2O72-, CeIV and molecular bromine and iodine has been studied.The fast kinetics of formation of the diamine radical cation and its further oxidation at a longer time scale, or with a higher concentration of the oxidants at a shorter time scale, were studied by following the absorption and decay of the radical cation, TMPD+ at 565 or 615 nm.The reaction was found to be second-order overall, but first-order with respect to and .The values of the second-order rate constants for the formation and decay of the radical cation were found to be in line with the oxidation potentials of the oxidants.Reduction of the radical cation by dithionite was found to regenerate the diamine, and the rate constant for this reaction was also determined.
- Maruthamuthu, Pichai,Venkatasubramanian, Lakshmanan,Dharmalingam, Periasamy
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- A new route to polykis(dialkylamino)benzenes and -naphthalenes based on protodefluorination of electron-rich fluoroaromatics: Anion radicals of arenes as a simple and effective alternative to 'classical' LAH-based systems
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A simple and effective procedure for protodefluorination of electron-rich fluoroaromatic compounds has been developed. It operates with aromatic anion radicals as reducing agents and shows superior results over 'classical' lithium aluminum hydride based s
- Sorokin, Vladimir Igorevich,Ozeryanskii, Valery Anatolievich,Borodkin, Gennady Sergeevich
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- A FACILE GENERATION OF RADICAL CATIONS VIA THE ACTION OF NITROXIDES
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Radical cations of aromatic amines and heteroaromatics were generated via the action of nitroxides in methylene chloride in the presence of trifluoroacetic acid.
- Liu, You-Cheng,Liu, Zhong-Li,Wu, Lung-Min,Chen, Ping
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- Charging a Li-O2 battery using a redox mediator
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The non-aqueous Li-air (O2) battery is receiving intense interest because its theoretical specific energy exceeds that of Li-ion batteries. Recharging the Li-O2 battery depends on oxidizing solid lithium peroxide (Li2O2), which is formed on discharge within the porous cathode. However, transporting charge between Li 2O2 particles and the solid electrode surface is at best very difficult and leads to voltage polarization on charging, even at modest rates. This is a significant problem facing the non-aqueous Li-O2 battery. Here we show that incorporation of a redox mediator, tetrathiafulvalene (TTF), enables recharging at rates that are impossible for the cell in the absence of the mediator. On charging, TTF is oxidized to TTF+ at the cathode surface; TTF+ in turn oxidizes the solid Li2O 2, which results in the regeneration of TTF. The mediator acts as an electron-hole transfer agent that permits efficient oxidation of solid Li 2O2. The cell with the mediator demonstrated 100 charge/discharge cycles.
- Chen, Yuhui,Freunberger, Stefan A.,Peng, Zhangquan,Fontaine, Olivier,Bruce, Peter G.
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- Continuum of outer- and inner-sphere mechanisms for organic electron transfer. Steric modulation of the precursor complex in paramagnetic (ion-radical) self-exchanges
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Transient 1:1 precursor complexes for intermolecular self-exchange between various organic electron donors (D) and their paramagnetic cation radicals (D+.), as well as between different electron acceptors (A) paired with their anion radicals (A .), are spectrally (UV-NIR) observed and structurally (X-ray) identified as the cofacial (π-stacked) associates [D, D+.] and [A-.· A], respectively. Mulliken-Hush (two-state) analysis of their diagnostic intervalence bands affords the electronic coupling elements (HOA), which together with the Marcus reorganization energies (λ) from the NIR spectral data are confirmed by molecular-orbital computations. The HDA values are found to be a sensitive function of the bulky substituents surrounding the redox centers. As a result, the steric modulation of the donor/acceptor separation (rDA) leads to distinctive electron-transfer rates between sterically hindered donors/acceptors and their more open (unsubstituted) parents. The latter is discussed in the context of a continuous series of outer- and inner-sphere mechanisms for organic electron-transfer processes in a manner originally formulated by Taube and co-workers for inorganic (coordination) donor/acceptor dyads-with conciliatory attention paid to traditional organic versus inorganic concepts.
- Rosokha, Sergiy V.,Kochi, Jay K.
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- Intermolecular electron-transfer reactions involving hydrazines
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The self-exchange electron-transfer (ET) rate constant k22 for 1,2,3,4,5-pentamethylferrocene was determined by NMR line broadening to be 8.5(±0.8) × 106 M-1 s-1 (25 °C, CD3CN/0.09 M Et4NBF
- Nelsen, Stephen F.,Chen, Ling-Jen,Ramm, Michael T.,Voy, Gilbert T.,Powell, Douglas R.,Accola, Molly A.,Seehafer, Troy R.,Sabelko, Jobiah J.,Pladziewicz, Jack R.
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- Chronoamperometry at Channel Electrodes. Experimental Applications of Double Electrodes
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Applications of transient experiments using double-channel electrodes are reported.The current response of a downstream detector electrode to a potential step at an upstream generator electrode is found to be in good agreement with theory.Such experiments are used to (i) demonstrate that the diffusion coefficient of the electrogenerated radical anion of p-chloranil in acetonitrile solution is 0.94 x 10-5 cm2 s-1, which contrasts markedly with that of the parent material (1.75 x 10-5 cm2 s-1), and (ii) characterize the nature of electrolytic processes occuring at the surface of porous silicon electrodes.The latter are shown to be electroactive throughout the depth of the porous surface layer.
- Compton, Richard G.,Coles, Barry A.,Gooding, Justin J.,Fisher, Adrian C.,Cox, Timothy I.
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- A general method for N-methylation of amines and nitro compounds with dimethylsulfoxide
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DMSO methylates a broad range of amines in the presence of formic acid, providing a novel, green and practical method for amine methylation. The protocol also allows the one-pot transformation of aromatic nitro compounds into dimethylated amines in the presence of a simple iron catalyst. Not just a solvent: DMSO methylates a broad range of amines in the presence of formic acid, providing a novel, green and practical method for amine methylation. The protocol also allows the one-pot transformation of aromatic nitro compounds into dimethylated amines in the presence of a simple iron catalyst. Copyright
- Jiang, Xue,Wang, Chao,Wei, Yawen,Xue, Dong,Liu, Zhaotie,Xiao, Jianliang
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- Monophotonic Ionization through a Long-Lived Ion Pair: N,N,N',N'-Tetramethyl-p-phenylenediamine in Acetonitrile Solution
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The monophotonic ionization of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) has been studied by means of transient absorption and transient photoconductivity measurements in acetonitrile solution.It has been concluded that the photoionization of TMPD is similar to that of 2,7-bis(dimethylamino)-4,5,9,10-tetrahydropyrene in acetonitrile solution.The formation and decay of the bound ion-pair state which is formed from the fluorescent state of TMPD and gives a quite similar absorption spectrum to the dissociated TMPD cation radical has been observed directly.The decay of the bound ion-pair state has been found to obey the reciprocal square root time dependence in the submicro to tens of microsecond time region.
- Hirata, Yoshinori,Mataga, Noboru
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- Two-electron oxidation of N,N,N′,N′-tetramethylphenylenediamine with a chromium(v) salen complex
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The oxidation of tetramethylphenylenediamine (TMPD) with (salen)Cr VO+ generates initially the 2-electron product TMPD 2+, followed by the reaction with excess TMPD to yield the radical cation, TMPD+. The kineti
- Chaka, Gezahegn,Bakac, Andreja
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- Water-assisted intramolecular electron transfer from the ring to the side chain in N,N,N′,N′-tetraalkyl-para-phenylenediamine radicals - The reverse of side chain deprotonation of radical cations
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In aqueous solution, the neutral radical formed by OH from one of the side-chain methyl groups of N,N,N′, N′,-tetramethyl-p-phenylenediamine (TMPD) is protonated by water to give the aromatic radical cation, TMDP+(see scheme). This reaction inv
- Steenken, Steen,Vieira, Abel J. S. C.
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- Reactions of Oxidizing Radicals with 4,6-Dihydroxypyrimidines as Model Compounds for Uracil, Thymine, and Cystosine
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The reactions of the oxidizing radicals OH, O-, SO4-, and Br2- with 4,6-dihydroxypyrimidine (4,6-DHP) and with 2- and 5-methyl-4,6-DHP were investigated by using in situ radiolysis and photolysis ESR and pulse radiolysis techniques.In the pH range 1-6 the OH radical reacts with these compounds -1 s-1> selectively by addition at C-5 to produce radicals characterized by two pairs of magnetically equivalent nitrogens and exchangeable protons.On the basis of the coupling constants and from the increased pKa value (8.3) of the radical from 4,6-DHP relative to that (5.3) of the parent compound, a diketo-type structure is suggested for the OH adducts.At pH 8-12 a base-catalyzed dehydration of the radical anions takes place which leads to the formation of species formally derived from the ionized parent compound by one-electron oxidation followed by deprotonation.These radicals can also be produced by reaction with SO4- or Br2-.Those from 4,6-DHP and from 2-Me-4,6-DHP were seen in two different protonation states: as a neutral radical between pH 3 and 5, and as the radical anion above pH ca. 5.Methyl groups on the 4,6-DHP molecule increase the rate of dehydration of the OH adducts.The O- radical reacts with the methylated 4,6-DHP's by H abstraction from the methyl groups.The structures of all the radicals from the 4,6-DHP's are compared with those from naturally occuring dioxopyrimidines such as the uracils.
- Novais, H. M.,Steenken, S.
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- UiO-type metal-organic frameworks with NHC or metal-NHC functionalities for: N-methylation using CO2 as the carbon source
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We demonstrate the first metal-organic framework (MOF) that catalyzes N-methylation of amines using 1 atm CO2 and phenylsilane under ambient conditions. Compared with its homogeneous analog, the incorporation of N-heterocyclic carbene (NHC) into the MOF provides more efficient catalysis with improved reaction kinetics, turnover numbers and recyclability. Moreover, the metalated NHC functionalized MOF achieves direct N-methylation of amines bearing carboxylate moieties, which are common building blocks in pharmaceutical chemistry.
- Zhang, Xu,Jiang, Yilin,Fei, Honghan
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- Spectral, kinetics, and redox studies on the transients formed on pulse radiolysis of aqueous solution of (4-methylthiophenyl)methanol
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Pulse radiolysis technique has been employed to investigate the nature and the redox properties of the transient species generated on radiolysis of aqueous solution of (4-methylthiophenyl)methanol (MTPM). Pulse radiolysis in 1,2-dichloroethane, reaction with specific one-electron oxidants (Cl2-, SO4-, Tl2+, Br) and reaction of OH radicals in acidic solution showed absorption bands at 320 and 545 nm; these are assigned to solute radical cation with positive charge on the benzene ring. OH-adduct was observed in neutral solution. The oxidation potential for MTPM/MTPM+ couple is determined to be 1.55 ± 0.04 V vs NHE. eaq- reacts with a bimolecular rate constant of 1.5 × 109 dm3 mol-1 s-1 and the transient absorption bands (λax = 320, 470 nm) are assigned to the solute radical anion. E0 value for MTPM/MTPM- couple is determined to be -1.84 ± 0.04 V vs NHE. The redox properties of the transient species formed on reaction with OH, H, and O- have been evaluated.
- Mohan,Mittal
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- Mechanism and Kinetics of the Photocatalyzed Oxidation of p-Phenylenediamines by Peroxydisulfate in the Presence of Tri-2,2'-bipyridylylruthenium(II)
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The autocatalytic oxidation of p-phenylenediamines with peroxydisulfate can be strongly enhanced by irradiation in the presence of tri-2.2'-bipyridylylruthenium(II).Ru(bpy)32+ acts as photosensitizer and photocatalyst.First, Ru(bpy)33+ is formed by quenching excited Ru*(bpy)32+ with S2O82-.Then the ruthenium(III) complex oxidizes p-phenylenediamine.The resulting Ru(bpy)32+ can start the cycle again.The photocatalytic oxidation of N,N-diethyl-p-phenylenediamine as well as the dark reactions were studied with stopped-flow techniques.The mechanism of this complex reaction is discussed in detail.
- Nickel, Ulrich,Chen, Yao-Hong,Schneider, Siegfried,Silva, Maria I.,Burrows, Hugh D.,Formosinho, Sebastiao J.
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- PATTERN OF OH RADICAL ADDITION TO CYTOSINE AND 1-, 3-, 5-, AND 6-SUBSTITUTED CYTOSINES. ELECTRON TRANSFER AND DEHYDRATION REACTIONS OF THE OH ADDUCTS.
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By use of the technique of pulse radiolysis with optical detection, the isomer distribution of the radicals formed in aqueous solution by addition of OH radicals to cytosine, 5-methylcytosine, 5-carboxylcytosine, 3-methylcytosine, 1-methylcyptosine, cytidine, 5-methylcytidine, cytidylic acid, 2 prime -deoxycytidine, 2 prime -deoxycytidylic acid, and 2-amino-4-hydroxy-6-methylpyrimidine has been determined by utilizing differences between the isomeric OH adducts with respect to electron-transfer reactions with the reductant N,N,N prime N prime -tetramethyl-p-phenylenediamine (TMPD) or the oxidant tetranitromethane (TNM). The radicals Cy-5-OH, formed by addition of OH to C(5) or cytosine (87% of the OH radicals), 3- and 5-methylcytosine (92% and 65%, respectively), 5-carboxylcytosine (82%), and 2-amino-4-hydroxy-6-methylpyrimidine (95%) reduce TNM to yield nitroform anion. The radicals Cy-6-OH, formed by addition to C(6), oxidize TMPD to yield TMPD** plus . The Cy-5-OH radicals undergo a base-catalyzed dehydration reaction to yield radicals that are able to oxidize TMPD to yield TMPD** plus multiplied by (times) .
- Hazra,Steenken
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- Metallopolymer Photochemistry. Photophysical, Photochemical, and Photoelectrochemical Properties of (bpy)2RuII< Sites Bound to Poly(4-vinylpyridine)
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The photochemical and photophysical properties of the polymer-bound chromophore Ru(bpy)2(PVP)22+ (PVP is poly(4-vinylpyridine)) have been investigated in homogeneous solution.Results have been obtained with polymers both dilute and concentrated in chromophore.Lifetime and quantum yield data are interpreted in terms of models of excited-state behavior previously proposed for analogous mopnomeric poly(pyridyl) complexes of Ru(II).Excited-state sites within the metallopolymers undergo oxidative and reductive electron-transfer quenching.The quenching reaction were investigated by Stern-Volmer quenching and conventional microsecond flash photolysis.Sensitization of n-TiO2 to visible light has been observed on a semiconductor coated with a film of the metallopolymer.
- Calvert, Jeffrey M.,Caspar, Jonathan V.,Binstead, Robert A.,Westmoreland, T. David,Meyer, Thomas J.
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- Chemistry of Singlet Oxygen. 37. One-Electron Oxidation of Tetramethylphenylenediamine by Singlet Oxygen
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Tetramethylphenylenediamine (TMPD) undergoes a one-electron transfer to (1)O2 in H2O; the formation of TMPD+. (Wuersters blue) is detected by laser flash spectroscopy.The formation of TMPD+. is competitively quenched by known (1)O2 quenchers.Furthermore, there is a large increase in TMPD+. formation in D2O, relative to H2O, as would be anticipated for a (1)O2 reaction.The rate (kτ) of electron transfer to (1)O2 is shown to be (3.3 +/- 1.5) x 109 M-1 s-1, close to the diffusion-controlled limit.The formation of observable ions does not take place in any solvent other than H2O(D2O), or with any other of the electron-rich aromatic amines studied.It is suggested that the formation of observable radical ions depends on the ease of ionization of the substrate and on the solvation of the resulting ions.
- Manring, Lewis E.,Foote, C. S.
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- Hollow Anatase TiO2 Octahedrons with Exposed High-Index {102} Facets for Improved Dye-Sensitized Photoredox Catalysis Activity
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The high activity of exposed facets and large surface area have significant effects on the performance of photocatalysts because most of the photoreactivity properties of materials are related to surface processes. The strategy of combining high-index facets and a hollow structure into one material will provide a new way for designing effective photocatalysts, possessing active exposed facets and a large surface area at the same time. However, fabricating one material with both high-index facets and a hollow structure is still a great challenge due to their thermodynamic instability. Here, hollow anatase TiO2 octahedrons exposed with high-index (102) facets (HTO-102) were successfully fabricated for the first time by a facile hydrothermal method using HF and H2O2 as morphology controlling agents. Compared with two other catalysts (a solid sharp octahedron with (101) facets (SSO-101) and a hollow sharp octahedron with (101) facets (HSO-101)), HTO-102 particles exhibit a better photochemical activity for the selective aerobic oxidation of organic sulfides under visible-light irradiation. Experimental results and theoretical calculations indicate that the excellent photocatalytic activity of HTO-102 particles is mainly due to the synergistic effects of its hollow structure and exposed high-index (102) facets.
- Wang, Fan,Sun, Liming,Li, Yanan,Zhan, Wenwen,Wang, Xiaojun,Han, Xiguang
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- Pattern of OH Radical Reaction with N6,N6,9-Trimethyladenine. Dehydroxylation and Ring Opening of Isomeric OH Adducts
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The OH radical reacts with N6,N6,9-trimethyladanine (A) in aqueous solution by addition to carbons 4 and 8 of the purine system (k = 8.4 * 109 M-1 s-1).The resulting radicals A4OH* and A(OH* undergo elimination of OH(1-) (identified by conductance; kel = 2*106 s-1) and ring opening (k = 2.3*105 s-1), respectively.The two types of reaction have different activation parameters.The (heterolytic) dehydroxylation reaction of A4OH* is inhibited by H(1+) and by OH(1-).The radical cation (the yield per OH* is 50percent) formed by elimination of OH(1-) from A4OH* is oxidizing (with respect to N,N,N',N'-tetramethyl-p-phenylenediamine); in contrast, A8OH* or its ring-opened product is reducing (toward tetranitromethane or viologens).On one-electron oxidation, A8OH* is converted into 8-hydroxy-N6,N6,9-trimethyladenine, which was measured by HPLC with optical and electrochemical detection.
- Vieira, A. J. S. C.,Steenken, S.
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- Photocatalytic selective aerobic oxidation of amines to nitriles over Ru/γ-Al2O3: The role of the support surface and the strong imine intermediate adsorption
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Hydroxyl coordinated ruthenium dispersed on the surface of γ-Al2O3 can be applied to the selective oxidation of amines with light irradiation and an atmospheric pressure of O2 at room temperature. Sunlight is also an effective light source for the selective aerobic oxidation of primary amines to corresponding nitriles. The high photocatalytic activity and selectivity over Ru/γ-Al2O3 originate from the adsorption of amines and imine intermediates on the abundant surface OH groups of the photocatalyst and further formation of Ru-amide species by ligand exchange of adsorbed amines and imine intermediates with adjacent exposed active Ru sites. Light is introduced to the system successfully via the formation of Ru-amide species, which are used as the light absorption sites of the photocatalytic selective oxidation of amines. Primary amines are directly converted to corresponding nitriles via a two-step oxidative dehydrogenation process.
- Zhu, Pengqi,Zhang, Jin,Wang, Jie,Kong, Peng,Wang, Yunwei,Zheng, Zhanfeng
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- β-Diketone boron difluoride dye-functionalized conjugated microporous polymers for efficient aerobic oxidative photocatalysis
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Incorporation of organic chromophores into conjugated micro/mesoporous polymers (CMPs) provides a promising avenue for developing recyclable heterogeneous photocatalysts by overcoming tedious separation and low reusability of homogeneous organic dye-based photocatalysts. However, the design principle and the underlying structure-property relationship for fabricating and selecting various organic dye-embedded CMPs for efficient photocatalysis have not been well-constructed so far. In this study, we described the rational fabrication of two new CMPsviathe one-step Sonogashira coupling using β-diketone boron difluoride dye as the key linker and commonly used building blocks (triphenylamine/triphenylbenzene) as the cores. The resulting boron-dye containing CMPs were efficiently employed as the metal-free photocatalysts in two typical aerobic oxidative organic transformations including coupling of benzylamine and oxidation of aryl boronic acids to corresponding aryl phenols, which have never been explored with other boron-dye-embedded CMPs. They exhibited superior photocatalytic performance compared to their boron-free counterparts due to their wide visible-light absorption, narrow optical bandgaps, and extended π-conjugation due to boron-complexation. The present study establishes β-diketone boron difluoride dyes as efficient building blocks for fabricating new CMP-based photocatalysts.
- Dong, Kaixun,Gong, Weitao,Hassan, Mehdi,Liu, Lu,Ning, Guiling
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- Electron Transfer Reactions and Mobile Holes in Radiolysis of Squalane. Time-Resolved FDMR Study
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Fluorescence detected magnetic resonance (FDMR) is applied to study ion-molecule reactions in squalane (2,6,10,15,19,23-hexamethyltetracosane).Several time-resolved pulsed FDMR experiments are suggested to measure rate constants of scavenging by aromatic solutes.These constants vary from 5E8 to 1.6E9 mol-1 dm3 s-1.The ion-molecule reactions of radical cations are somewhat slower than reactions of radical anions.The scavenging of the alkane hole is significantly faster than ion-molecule reactions of molecular cations.The mobile hole decays on a time scale of several tens of nanoseconds.These FDMR results are in accord with our recent work on transient absorption spectroscopy in radiolysis of squalane.
- Shkrob, I. A.,Trifunac, A. D.
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- Catalyst-free one-pot reductive alkylation of primary and secondary amines and N,N-dimethylation of amino acids using sodium borohydride in 2,2,2-trifluoroethanol
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A simple and convenient procedure for the reductive alkylation of primary and secondary amines and N,N-dimethylation of amino acids is described using sodium borohydride as a reducing agent in 2,2,2- trifluoroethanol without use of a catalyst or any other additive. The solvent can be readily recovered from reaction products in excellent purity for direct reuse. Georg Thieme Verlag Stuttgart - New York.
- Tajbakhsh, Mahmood,Hosseinzadeh, Rahman,Alinezhad, Heshmatollah,Ghahari, Somayeh,Heydari, Akbar,Khaksar, Samad
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- Bandgap engineering in benzotrithiophene-based conjugated microporous polymers: a strategy for screening metal-free heterogeneous photocatalysts
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Metal-free conjugated microporous polymers (CMPs) as visible-light active and recyclable photocatalysts offer a green and sustainable alternative to classical metal-based photosensitizers. However, the strategy for screening CMP-based heterogeneous photocatalysts has not been interpreted up to now. Herein, we present a general strategy for obtaining excellent solid photocatalysts, which is to implement bandgap engineering in the same series of materials. As a proof of concept, three conjugated porous materials containing benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene building blocks (BTT-CMP1, BTT-CMP2 and BTT-CMP3) were successfully constructed. They possess permanent porosity with a large specific surface area and excellent stability. By changing the linker between benzotrithiophene units, the bandgaps, energy levels and photoelectric performances including the absorption, transient photocurrent responses and photocatalytic performances of BTT-CMPs could be handily modulated. Indeed, BTT-CMP2 displayed the best catalytic activity for visible-light-induced synthesis of benzimidazoles among the three CMP materials, even higher than that of small molecule photocatalysts. As a metal-free photocatalyst, interestingly, the screened BTT-CMP2 also showed extensive substrate applicability and outstanding recyclability. Additionally, we have the opinion that this strategy will prove to be a guiding principle for screening superior CMP-based photocatalysts and broaden their application fields.
- Han, Songjie,Li, Ziping,Ma, Si,Zhi, Yongfeng,Xia, Hong,Chen, Xiong,Liu, Xiaoming
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- Metal-Free Photoredox-Catalyzed Hydrodefluorination of Fluoroarenes Utilizing Amide Solvent as Reductant
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A metal-free photoredox-catalyzed hydrodefluorination of fluoroarenes was achieved by using N,N,N’,N’-tetramethyl-para-phenylenediamine (1) as a strong photoreduction catalyst. This reaction was applicable not only to electron-rich monofluoroarenes but also to polyfluoroarenes to afford non-fluorinated arenes. The experimental mechanistic studies indicated that the amide solvent NMP plays an important role for regeneration of the photocatalyst, enabling additive-free photoreduction catalysis.
- Toriumi, Naoyuki,Yamashita, Kazuya,Iwasawa, Nobuharu
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- One-Electron Oxidation in Irradiated Carbon Tetrachloride Solutions of ZnTPP, TMPD, and Phenols
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One-electron oxidation of phenol, p-methoxyphenol, N,N,N',N'-tetramethyl-p-phenylenediamine, chlorpromazine, and zinc tetraphenylporphyrin was studied by pulse radiolysis in carbon tetrachloride solutions.Phenols form phenoxyl radicals and the other compounds form cation radicals with yields strongly dependent on solute concentration.The highest yield in deoxygenated solutions approached G = 4.In the presence of oxygen an additional oxidation step is observed owing to CCl3O2. radicals and the overall oxidation yield approached G = 8.ZnTPP was found to be oxidized to the cation radical without any side effects, unlike oxidation in 1,2-dichloroethane which was accompanied by demetallation owing to HCl production.
- Grodkowski, J.,Neta, P.
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- Simplified preparation of a graphene-co-shelled Ni/NiO@C nano-catalyst and its application in theN-dimethylation synthesis of amines under mild conditions
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The development of Earth-abundant, reusable and non-toxic heterogeneous catalysts to be applied in the pharmaceutical industry for bio-active relevant compound synthesis remains an important goal of general chemical research.N-methylated compounds, as one of the most essential bioactive compounds, have been widely used in the fine and bulk chemical industries for the production of high-value chemicals. Herein, an environmentally friendly and simplified method for the preparation of graphene encapsulated Ni/NiO nanoalloy catalysts (Ni/NiO@C) was developed for the first time, for the highly selective synthesis ofN-methylated compounds using various functional amines and aldehydes under easy to handle, and industrially applicable conditions. A large number of primary and secondary amines (more than 70 examples) could be converted to the correspondingN,N-dimethylamines with the participation of different functional aldehydes, with an average yield of over 95%. A gram-scale synthesis also demonstrated a similar yield when compared with the benchmark test. In addition, it was further proved that the catalyst could easily be recycled because of its intrinsic magnetism and reused up to 10 times without losing its activity and selectivity. Also, for the first time, the tandem synthesis ofN,N-dimethylamine products in a one-pot process, using only a single earth-abundant metal catalyst, whose activity and selectivity were more than 99% and 94%, respectively, for all tested substrates, was developed. Overall, the advantages of this newly developed method include operational simplicity, high stability, easy recyclability, cost-effectiveness of the catalyst, and good functional group compatibility for the synthesis ofN-methylation products as well as the industrially applicable tandem synthesis process.
- Liu, Jianguo,Ma, Longlong,Song, Yanpei,Zhang, Mingyue,Zhuang, Xiuzheng
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supporting information
p. 4604 - 4617
(2021/06/30)
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- Synergistic catalysis of Cu+/Cu0 for efficient and selective N-methylation of nitroarenes with para-formaldehyde
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In this paper, an inexpensive heterogeneous copper nanoparticles catalyst derived from CuAl-layered double hydroxide via an in situ topotactic transformation process was developed. Cu nanoparticles with uniform size were homogeneously dispersed on amorphous Al2O3 with strong metal-support interaction. Characterization results reveals that the Cu0 and Cu+ were simultaneously formed with Cu+ species as the dominant sites on the surface during the reduction process. The resultant catalyst Cu/Al2O3 demonstrates high catalytic activity, selectivity and durability for the reductive N-methylation of easily available nitroarenes in a cost-efficient, environmentally friendly and cascade manner. A broad spectrum of nitroarenes could be efficiently N-methylated to their corresponding N,N-dimethyl amines with good compatibility of various functional groups. The protocol is also applicable for the late-stage functionalization of biologically and pharmaceutically active nitro molecules. A structure-function relationship discloses that Cu0 and Cu+ sites on the surface pronouncedly boosts the reaction efficiency in a synergistic manner, in which Cu0 could facilitate H2 production and N-methylation of anilines, while Cu+ is considerably more active and participates in the overall process of the selective N-methylation of nitroarenes. Moreover, the catalyst also showed a strong stability and could be easily separated for successive reuses without an appreciable loss in activity and selectivity.
- Dong, Xiaosu,Wang, Zhaozhan,Yuan, Youzhu,Yang, Yong
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p. 304 - 313
(2019/07/02)
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- Highly Selective N-Monomethylanilines Synthesis from Nitroarene and Formaldehyde via Kinetically Excluding of the Thermodynamically Favorable N,N-Dimethylation Reaction
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The synthesis of N-monomethylamine remains a challenging topic because the N,N-dimethylation reaction is thermodynamically favorable. In this work, the kinetically controlled N-monomethylamine synthesis from nitroarene and paraformaldehyde/H2 is reported to have superhigh N-monomethylamine selectivity in the presence of a Pd/TiO2 catalyst. The superior selectivity should be attributed to the preferential adsorption of the primary amine over N-monomethylamine on the Pd/TiO2 surface, as elucidated by NH3/Me2NH-TPD, while the excellent catalytic activity could be associated with the good H2 activation ability and high amine adsorbing capacity of the catalyst, as elucidated by NH3-TPD and H2-TPR tests. Good results were obtained with a variety of nitroarenes containing methyl, methoxyl, hydroxyl, fluoride, trifluoromethyl, ester, and amide substituents as starting materials, and the potential synthetic utility of this protocol in pharmaceutical is illustrated by N-monomethylation of drug molecules, such as clinidipine, nimesulide, procaine, and methyl aminosalicylate.
- Wang, Hongli,Yuan, Hangkong,Yang, Benqun,Dai, Xingchao,Xu, Shan,Shi, Feng
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p. 3943 - 3949
(2018/05/23)
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- One-pot synthesis of N,N-dimethylanilines from nitroarenes with skeletal Cu as chemoselective catalyst
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A range of N,N-dimethylanilines were synthesized with excellent yields in one-pot by the hydrogenation and alkylation of nitroarenes with H2 and HCHO over quenched skeletal Cu catalyst, which provides a facile, economical, and environmentally benign alternative methodology for C-N bonds formation.
- Rong, Zeming,Zhang, Wenjun,Zhang, Peng,Sun, Zhuohua,Lv, Jinkun,Du, Wenqiang,Wang, Yue
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p. 115 - 118
(2013/09/02)
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- Application of Marcus cross-relation to mixed inorganic-organic redox couples. A stopped-flow study of the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine with various oxidants
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The rate constants of the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPPD) are measured in water by means of stopped-flow techniques using different inorganic ions, like Fe(CN)63-, MnO4-, Co(NH3)63+, Ru(OH)63+. The rates do not depend on the different oxidation potentials, but can be correlated well with calculated rate constants from the Marcus cross-relation. The electron self-exchange rates of the inorganic oxidants range over nine orders of magnitude. Measurements were performed at T = 293 K within a pH-range of 7-9.
- Grampp, Guenter,Landgraf, Stephan,Sabou, Dana,Dvoranova, Dana
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p. 178 - 180
(2007/10/03)
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- N-substituted p-phenylenediamines as peroxidase and laccase substrates
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N-Substituted p-phenylenediamines, such as 1-(N,N-dimethylamino)-4-(4-morpholinyl)benzene (AMB), 1-(1-piperidinyl)-4-(4-morpholinyl)benzene (PMB), 1,4-di(1-piperidinyl)benzene (DPB), 1,4-di(4-morpholinyl)benzene (DMB) and N-methyl-N-ethyl-4-(4-morpholinyl) benzylamine (MEMB) are oxidized in a peroxidase-catalyzed process following radical cation formation. At pH 7 an apparent bimolecular constant (kox) varied from 1.8 to 43.6μM-1s-1 for horseradish peroxidase (HRP) and peroxidase from Coprinus cinereus (CiP). The limiting step of the substrate oxidation was reduction of compound II, and the steady-state constant of AMB oxidation (13.2 μM-1s-1) was consistent with a constant (11.9 μM-1S-1) determined by a stopped-fiow method. kox of compound I reduction with the same substrates was 23.1 μM-1s-1. CiP showed a broad pH activity at pH 6-10, whereas the activity of the HRP-catalyzed reaction dropped at pH 8.0. The apparent pKa value for HRP was 7.35 and 9.7 for CiP. The same substrates are also catalytically oxidized by fungal laccase from Polyporus pinsitus. kox constants were considerably lower than in peroxidase catalysis and varied from 0.08 μM-1s-1 to 1.74 μM-1s-1. Optimal activity for AMB oxidation was obtained at pH 5-5.5 with apparent pKa values of 5.5 and 5.3. The correlation between the reaction driving force and electron transfer rate was analyzed for both types of reaction. Acta Chemica Scandinavica 1998.
- Krikstopaitis, Kastis,Kulys, Juozas,Pedersen, Anders Hjelholt,Schneider, Palle
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p. 469 - 474
(2007/10/03)
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- Indirect determination of self-exchange electron transfer rate constants
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Second-order rate constants k(ij)(obsd) measured at 25 °C in acetonitrile by stopped-flow spectrophotometry for forty-four electron transfer (ET) reactions among fourteen 0/+1 couples [three aromatic compounds (tetrathiafulvalene, tetramethyltetraselenafulvalene, and 9,10-dimethyl- 9,10-dihydrophenazine), four 2,3-disubstituted 2,3-diazabicyclo[2.2.2]octane derivatives, six acyclic hydrazines, and the bridgehead diamine 1,5- diazabicyclo[3.3.3]undecane] and seventeen compounds and forty-seven reactions from a previous study (J. Am. Chem. Soc. 1997, 119, 5900) [three p- phenylenediamine derivatives, four ferrocene derivatives, and ten tetraalkylhydrazines] are discussed. When all 91 k(ij)(obsd) values are simultaneously fitted to Marcus's adiabatic cross rate formula k(ij)(calcd) = (k(ii)k(jj)K(ij)f(ij))(1/2), ln f(ij) = (ln K(ij))(2/4) ln((kii)k(jj)/Z2), best-fit self-exchange rate constants, k(ii)(fit), are obtained that allow remarkably accurate calculation of k(ij)(obsd); k(ij)(obsd)/k(ij)(calcd) is in the range 0.5-2.0 for all 91 reactions. The average difference without regard to sign, |ΔΔG(+)(ij)|, between observed cross reaction activation free energy and that calculated using the k(ii)(fit) values and equilibrium constants is 0.13 kcal/mol. The ΔG(+)(ii)(fit) values obtained range from 2.3 kcal/mol for tetramethyltetraselenafulvalene(0/+) to 21.8 kcal/mol for tetra-n-propylhydrazine(0/+), corresponding to a factor of 2 x 1014 in k(ii)(fit). The principal factor affecting k(ii)(fit) for our data appears to be the internal vertical reorganization energy (λ(v)), but k(ii)(fit) values also incorportate the effects of changes in the electronic matrix coupling element (V). Significantly smaller V values for ferrocenes and for hydrazines with alkyl groups larger than methyl than for aromatics and tetramethylhydrazine are implied by the observed ΔG(+)(ii)(fit) values.
- Nelsen, Stephen F.,Ismagilov, Rustem F.,Gentile, Kevin E.,Nagy, Mark A.,Tran, Hieu Q.,Qu, Qinling,Halfen, DeWayne T.,Odegard, Amy L.,Pladziewicz, Jack R.
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p. 8230 - 8240
(2007/10/03)
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- Estimation of self-exchange electron transfer rate constants for organic compounds from stopped-flow studies
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Second-order rate constants k12(obsd) measured at 25 °C in acetonitrile by stopped-flow for 47 electron transfer (ET) reactions among ten tetraalkylhydrazines, four ferrocene derivatives, and three p- phenylenediamine derivatives are discussed. Marcus's adiabatic cross rate formula k12(calcd) = (k11 k22 k12f12)(1/2) , Inf12 = (In K12)(2/4) ln(k11k22/Z2) works well to correlate these data. When all k12(obsd) values are simultaneously fitted to this relationship, best-fit self-exchange rate constants, k(ii)(fit), are obtained that allow remarkably accurate calculation of k12(obsd); k12(obsd)lk12'(calcd) is in the range of 0.55-1.94 for all 47 reactions. The average ΔΔG(ii)≠ between observed activation free energy and that calculated using k(ii)(fit) is 0.13 kcal/mol. Simulations using Jortner vibronic coupling theory to calculate k12 using parameters which produce the wide range of k(ii) values observed predict that Marcus's formula should be followed even when V is as low as 0.1 kcal/mol, in the weakly nonadiabatic region. Tetracyclohexyl-hydrazine has a higher k(ii) than tetraisopropylhydrazine by a factor of ca. 10. Replacing the dimethylamino groups of tetramethyl-p-phenylenediamine by 9- azabicyclo[3.3.1]nonyl groups has little effect on k(ii), demonstrating that conformations which have high intermolecular aromatic ring overlap are not necessary for large ET rate constants. Replacing a γ CH2 group of a 9- azabicyclo[3.3.1]nonyl group by a carbonyl group lowers k(ii) by a factor of 17 for the doubly substituted hydrazine and by considerably less for the doubly substituted p-phenylenediamine.
- Nelsen, Stephen F.,Ramm, Michael T.,Ismagilov, Rustem F.,Nagy, Mark A.,Trieber II, Dwight A.,Powell, Douglas R.,Chen, Xi,Gengler, Jamie J.,Qu, Qinling,Brandt, Jennifer L.,Pladziewicz, Jack R.
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p. 5900 - 5907
(2007/10/03)
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- Reduction potentials of flavonoid and model phenoxyl radicals. Which ring in flavonoids is responsible for antioxidant activity?
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Model phenoxyl and more complex flavonoid radicals were generated by azide radical induced one-electron oxidation in aqueous solutions. Spectral, acid-base and redox properties of the radicals were investigated by the pulse radiolysis technique. The physicochemical characteristics of the flavonoid radicals closely match those of the ring with the lower reduction potential. In flavonoids which have a 3,5-dihydroxyanisole (catechins), or a 2,4-dihydroxyacetophenone (hesperidin, rutin, quercetin)-like A ring and a catechol- or 2-methoxyphenol-like B ring, the antioxidant active moiety is clearly the B ring [reduction potential difference between the model phenoxyls is ΔE(A-B ring models) > 0.1 V]. In galangin, where the B ring is unsubstituted phenyl, the antioxidant active moiety is the A ring. Even though the A ring is not a good electron donor, E7, > 0.8/NHE V, it can still scavenge alkyl peroxyl radicals, E7, = 1.06 V, and the Superoxide radical, E7 > 1.06 V. Quercetin is the best electron donor of all investigated flavonoids (measured E10.8 = 0.09 V, and calculated E7 = 0.33 V). The favourable electron-donating properties originate from the electron donating O-3 hydroxy group in the C ring, which is conjugated to the catechol (B ring) radical through the 2,3-double bond. The conjugation of the A and B rings is apparently minimal, amounting to less than 2.5% of the substituent effect in either direction. Thus, neglecting the acid-base equilibria of the A ring, and using those of the B ring and the measured values of the reduction potentials at pH 3,7 and 13.5, the pH dependence of the reduction potentials of the flavonoid radicals can be calculated. In neutral and slightly alkaline media (pH 7-9), all investigated flavonoids are inferior electron donors to ascorbate. Quercetin, E7 = 0.33 V, and gallocatechins, E7 = 0.43 V, can reduce vitamin E radicals (assuming the same reduction potential as Trolox C radicals, E7 = 0.48 V). Since all investigated flavonoid radicals have reduction potentials lower than E7 = 1.06 V of alkyl peroxyl radicals, the parent flavonoids qualify as chain-breaking antioxidants in any oxidation process mediated by these radicals.
- Jovanovic, Slobodan V.,Steenken, Steen,Hara, Yukihiko,Simic, Michael G.
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p. 2497 - 2504
(2007/10/03)
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- Reactivity of a 17e organometallic radical in aqueous solution
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Laser flash photolysis of [(C5H4CO2-)W(CO)3] 2 in aqueous solution at 460-532 nm induces homolysis of the metal-metal bond with formation of the 17e radical (C5H4CO2-)W(CO)3. The rate constant for its dimerization is 3.0 × 109 L mol-1 s-1 at 23°C. The radical reacts with haloacetate ions, pseudohalo- and halometal complexes by atom transfer. The reactivity trend is normal (RI > RBr > RCl). The reaction between this radical with t-BuOOH in water occurs similarly with a rate constant of 1.37 × 106 L mol-1 s-1. For electron-transfer reactions, the radical acts as both reductant and oxidant. It oxidizes tetramethylphenylenediamine to TMPD.+ in aqueous solution with a rate constant of 1.49 × 107 mol-1 s-1. The radical reduces MV2+ and Fe(CN)63- to MV.+ and Fe(CN)64- with rate constants of 2.0 × 106 and 6.06 × 107 L mol-1 s-1, respectively. The phosphine Ph2PPhSO3Na accelerates the reaction of the radical with MV2+ very mildly. This may bear on the question of whether the tungsten-phosphine adduct is a species with 19 valence electrons, a slipped cyclopentadienyl ring, or a phosphoranyl radical.
- Zhu, Zuolin,Espenson, James H.
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p. 1893 - 1898
(2008/10/08)
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- Photosensitized lipid peroxidation by cinoxacin and its photoproducts. Involvement of a derived peroxide in its phototoxicity
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The photodegradation process of the phototoxic antibacterial agent cinoxacin was studied. The products of its photolysis under UV-B and aerobic conditions were first isolated and identified. A peroxidic photoproduct formed during the reaction showed a high oxidizing power, indicative of its ability to induce oxidative stress. This was clearly shown by model studies with reduced glutathione and cysteine, which were converted into the corresponding disulfides. The possible involvements of an electron transfer mechanism in these processes was suggested by the generation of the radical cation of N,N,N',N'-tetramethylphenylenediamine (TMP+) upon reaction of this peroxidic product with TMP. Cinoxacin and its photoproducts were found to be active when examined by photohemolysis on human erythrocytes, and lipid photoperoxidation on linoleic acid.
- Vargas,Rivas,Canudas
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p. 742 - 745
(2007/10/02)
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- Electron-transfer reactions of alkyl peroxy radicals
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One-electron-transfer reactions of alkyl peroxy radicals were studied by pulse radiolysis of aqueous solutions. At pH 13, the methyl peroxy radical was found to rapidly, k = 1 × 105-4.9 × 107 s-1, and quantitatively oxidize various organic substrates with E13 = 0.13-0.76 V vs NHE. On the other hand, this radical was unreactive with compounds with E13 ≥ 0.85 V. Consequently, E13 of the methyl peroxy radical is higher than 0.76 V and lower than 0.85 V, which means that E7 is in the range 1.02-1.11 V. At pH 8, the rate constants of the oxidation of four ferrocene derivatives by the alkyl peroxy radicals ranged from 7.1 × 104 M-1 s-1 for ferrocenedicarboxylate (E8 = 0.66 V) to 2.3 × 106 M-1 s-1 for (hydroxymethyl)ferrocene (E8 = 0.42 V). These rate constants were used to evaluate the reduction potential and self-exchange rate of alkyl peroxy radicals in neutral media from the Marcus equation. The calculated E7 = 1.05 V is in excellent agreement with the estimated E7 = 1.02-1.11 V and with one of the perviously published values E7 = 1.0 V, but the value is in excellent agreement higher than the other E7 ~ 0.6 V. It is suggested that the high reorganization energy, λ = 72 kcal mol-1 redox couple originates from the requirement for solvent reorganization due to the solvation of hydroperoxide anion in the transition state. In support of this are the activation parameters of the reaction of the methyl peroxy radical with uric acid. The activation entropy is 9 eu lower at pH 7.3 than it is at pH 13.2, whereas the activation enthalpies are unchanged. The importance of entropy control was verified in the reactions of cyclohexyl peroxy radicals with α- and δ-tocopherol in aerated cyclohexane (ΔH+ ≈ 0 kcal/mol, and ΔS+ = -25 and -26 eu). The implications of these findings on the inactivation of alkyl peroxy radicals in general are discussed.
- Jovanovic, Slobodan V.,Jankovic, Ivana,Josimovic, Ljubica
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p. 9018 - 9021
(2007/10/02)
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- Radiolytic Reductions and Oxidations in Dimethyl Sulfoxide Solutions. Solvent Effects on Reactivity of Halogen Atom Complexes
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Radiolysis of dimethyl sulfoxide (DMSO) solutions containing various additives was used to achieve clean one-electron reduction or oxidation of solutes.Pulse radiolysis of benzoquinone in DMSO solutions containing acetone and triethylamine permitted conversion of all primary radicals into reducing species.The total yield of reduction in the γ-radiolysis of methyl viologen solutions was found to be 0.37 μmol/J.In the pulse radiolysis of TMPD and triphenylamine in aerated DMSO containing LiCl and/or CCl4, all the primary radicals were converted into oxidizing species and gave a maximum yield of 0.39 μmol/J.In the latter systems, oxidation was partly by halogen atom complexes.The reactivity of complexes of DMSO (DMSO*Cl, DMSO*Br) and of halide ions (Br2.1-, I2.1-) was examined for several organic compounds.DMSO*Cl oxidizes chlorpromazine, triphenylamine, and zinc porphyrin with rate constants of the order of 1E7-1E8 M-1 s-1, and the rates increase upon addition of CH2Cl2 as well as upon addition of water and formamide.DMSO*Cl also reacts with olefins by addition of Cl to the double bond; the rate constants increase upon increasing the electron-donating properties of the substituents on the double bond.The rate constants for oxidation of chlorpromazine by Br2.1- and I2.1- increase by more than 2 orders of magnitude upon changing the solvent from DMSO gradually to water.The change was less with acetonitrile/water mixtures, and the difference is probably due to differences in ion solvation.
- Kumar, M.,Neta, P.
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p. 3350 - 3354
(2007/10/02)
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- Formation of Radical Cation and Dication of 1,3,4,6-Tetrakis(isopropylthio)-2λ4δ2-thienothiophene and their Reactions with Nucleophiles
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1,3,4,6-Tetrakis(isopropylthio)-2λ4δ2-thienothiophene 1 formed the complex 2 with I2 in hexane at -30 deg C.The ESR spectrum of the complex 2 in MeCN solution showed that the spin densities in the ?-electron system are large in the 1-, 3-, 4- and 6-positions.The complex 2 reacted with amines in MeCN to give the C-C coupling products 4a-c in high yields.The oxidation of 1 with I2 in the presence of aniline in benzene gave the thiophene derivative 5 in a high yield by hydrogen abstraction at the 3-position.The compound 1 was oxidized to its dication byNOBF4.The dication reacted with amines, alcohols and water to give the ring-opening products 10-14 and with thiols and NaBH4 to give the adducts 23-25.
- Tsubouchi, Akira,Kitamura, Chitoshi,Matsumura, Noboru,Inoue, Hiroo
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p. 2935 - 2940
(2007/10/02)
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- Nucleophilic substitution versus electron transfer: 2. SN2 at fluorine and electron transfer are competing and different pathways in electrophilic fluorinations
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A comparison between the observed rate constants of electrophilic fluorinations and the calculated rates for electron transfer gives for the first time kinetic proof that nucleophilic attack at fluorine has to occur in order to explain the high reaction rates. The low yields of fluorinated products under conditions where ET becomes important are an indication that SN2 and ET are competing and different pathways.
- Differding,Wehrli
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p. 3819 - 3822
(2007/10/02)
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- INVESTIGATION OF ELECTRON TRANSFER REACTIONS BETWEEN AROMATIC AND QUINOID SYSTEMS.
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A classical organic redox reaction is the conversion of an aromatic compound from its reduced form R to a semioxidized state S, and further to a totally oxidized (quinoid) species T. Complex redox systems are present in a reaction of quinoid and aromatic forms derived from different parent compounds. In this case, the exchange of one or two electrons in one step between T and R can be distinguished experimentally. These reactions were investigated in a stopped-flow apparatus with optical detection. In the system N,N,N prime ,N prime -tetramethyl-para-phenylene-diamine/N,N-dimethyl-para- phenylenediamine the rate constants for all elementary reactions have been determined. Protonated, and unprotonated R were found to be reactive.
- Goez,Jaenicke,Nickel
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p. 459 - 467
(2007/10/02)
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- Aminopyrine and Antipyrine Free Radical-cations: Pulse Radiolysis Studies of One-electron Transfer Reactions
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Absolute rate constants for the reaction of a variety of electrophilic free radicals with the pyrazoline derivatives aminopyrine and antipyrine have been measured by pulse radiolysis.In the case of aminopyrine the resulting radical cation is a particularly stable species ε325 5.35*103 dm3 mol-1 cm-1).Both compounds are readily oxidised to their respective radical-cations with the one-electron oxidation potential of antipyrine (E0 1.1-1.6 V) being higher than that of aminopyrine (E0 0.26-0.5 V).Studies of the reaction of the radical-cations with reducing agents suggest that aminopyrine in particular may prove to be a useful reference compound in studies of free radical one-electron oxidations.
- Forni, Luigi G.,Mora-Arellano, Victor O.,Packer, John E.,Willson, Robin L.
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p. 1579 - 1584
(2007/10/02)
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- Acetonylperoxyl Radicals, CH3COCH2O2: A Study on the γ-Radiolysis and Pulse Radiolysis of Acetone in Oxygenated Aqueous Solutions
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Hydroxyl radicals from the radiolysis of N2O/O2 (4:1)-saturated aqueous solutions of acetone (1E-3 mol dm-3) react with the solute by H-abstraction thereby forming acetonyl radicals.As shown by pulse radiolysis, the acetonyl radicals rapidly add oxygen (k = 3E9 dm3 mol-1 s-1) thereby forming acetonylperoxyl radicals which decay by second-order kinetics (2k = 8E8 dm3 mol-1 s-1).Under steady-state radiolysis conditions (0.24 Gy s-1) the products (G values in parentheses) are methylglyoxal (2.5), hydroxyacetone (0.5), formaldehyde (1.6), acids (1.7), carbon dioxide (0.5), organic (hydro)peroxides (0.4), hydrogen peroxide (2.2), and G (oxygen uptake) has been determined at 5.2.In the decay of the acetonylperoxyl radicals the major process (slightly less than one half) leads in a concerted reaction to two molecules of methylglyoxal and one molecule of hydrogen peroxide.The Russel mechanism which yields one molecule of methylglyoxal, hydroxyacetone and oxygen contributes about one fifth as does the breakdown into two molecules of formaldehyde, one molecule of oxygen and two acetyl radicals.Carbon dioxide, formaldehyde and acetic acid are among the products which result from the acetylperoxyl radicals formed upon oxygen addition to the acetyl radicals.About one tenth of the organic peroxyl radicals is converted into hydroperoxides by O2 produced as a byproduct in the water radiolysis. - Key words: Pulse Radiolysis, Acetone, Acetonylperoxyl Radical, Superoxide Radical
- Zegota, Henryk,Schumann, Man Nien,Schulz, Dorothea,Sonntag, Clemens von
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p. 1015 - 1022
(2007/10/02)
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- The Oxidation of Trimethylamine by OH Radicals in Aqueous Solution, as Studied by Pulse Radiolysis, ESR, and Product Analysis. The Reactions of the Alkylamine Radical Cation, the Aminoalkyl Radical, and the Protonated Aminoalkyl Radical
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Hydroxyl radical reactions with trimethylamine in aqueous solution lead to the formation of the aminoalkyl radical (A(.)) and its conjugated acid (AH(+.)) as well as to the alkylamine radical cation (CH3)3N(+.) (N(+.)).These radicals are transformed into each other by hydrolytic reactions, e.g. Radicals AH(+.) are more acidic (pKa ca. 3.6) than the radicals N(+.) (pKa ca. 8.0).Consequently, N(+.) predominate over AH(+.) under quasi equilibrium conditions (e.g. in the presence of phosphate buffer) and are the only species observed by ESR in acid solutions.Reacting with the protonated amine, OH radicals abstract hydrogen at nitrogen and at carbon with comparable ease.Reaction of OH radicals with the free amine may initially also generate N(+.), beside H-abstraction at carbon.Radicals A(.) absorb more strongly at 260 nm (ε = 3390 dm3mol-1cm-1) than the radical cation N(+.) (ε = 950 dm3mol-1cm-1).Radical A(.) has reducing properties whereas radicals AH(+.) and N(+.) have oxidizing properties and hence can be monitored with p-nitroacetophenone (the reducing radicals), and Fe(CN)6(4-), N,N'-tetramethyl-p-phenylenediamine and 2,2'-azinobis-(3-ethyl-benzthiazoline-6-sulphonate) (the oxidizing radicals).These radicals mainly (>/=85percent) disproportionate, one of the products being formaldehyde. - Keywords: Radiation Chemistry, Amines, Electron Transfer, Hydrogen Abstraction, Reaction Kinetics
- Das, Suresh,Sonntag, Clemens von
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p. 505 - 513
(2007/10/02)
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- REACTIONS OF CHLORINE DIOXIDE IN DICHLOROMETHANE I. FORMATION OF RADICAL CATIONS IN ACID MEDIA
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Chlorine dioxide oxidises electron rich organic compounds to the corresponding radical cations in dichloromethane/TFA medium.In a different experimental set up using alkaline biphasic solvent system, its utility as hydrogen abstractor has been capitalized in the preparation of diazodiphenyl methane in good yield.
- Handoo, Kishan L.,Handoo, S. K.,Gadru, Kanchan,Kaul, Anju
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p. 1765 - 1768
(2007/10/02)
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- CHARGE-TRANSFER COMPLEXES AND THE CATALYTIC EFFECT OF GALLIUM CHLORIDE IN THE DIELS-ALDER REACTION
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An analysis was made of the factors giving rise to the significant catalytic effect in the Diels-Alder reaction in the presence of Lewis acids.It was shown that changes in the structure and localization energy cannot be the reason for the observed effect.From spectroscopic investigation of the ?,?-complexes of hexamethylbenzene with unactivated N-arylmaleimides and with N-arylmaleimides activated by the formation of n, V complexes it follows that the energy of the LUMO decreases by 0.7 - 1.1 eV in this transition.The obtained results are regarded as experimentalevidence for control of the catalytic effect by the stabilization energy of the transition state resulting from the increased interaction between the frontier orbitals.
- Kiselev, V. D.,Shakirov, I. M.,Konovalev, A. I.
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p. 1324 - 1328
(2007/10/02)
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