90-44-8Relevant articles and documents
ON THE MECHANISM OF THE CATHODIC REDUCTION OF ANTHRAQUINONE TO ANTHRONE.
Beck,Heydecke
, p. 37 - 43 (1987)
The cathodic reduction of anthraquinone in 85% H//2SO//4 at cathodes of glassy carbon or mercury has been investigated. Voltammetric curves exhibit two steps at plus 0. 23 and plus 0. 10 V vs. SHE. The limiting current densities show a ratio between 4:0 via 1:1 to 1:3, depending on the experimental conditions. Experiments at the RRDE indicate two reoxidizable intermediates. We derive a mechanism from our findings, involving the electrochemical formation of these intermediates, anthrasemiquinone AQH multiplied by (times) and anthrahydroquinone AQH//2. Both are subject to a bimolecular follow up reaction (disproportionation) to yield AQH//2 and anthrone. The rate constants are estimated to be 2. 10**3 and 3. 10**4 1 mol** minus **1 s** minus **1, respectively. Anthrone is the only reduction product which could be isolated.
Enol-keto tautomerism of 9-anthrol and hydrolysis of its methyl ether
McCann, Geraldine M.,McDonnell, Claire M.,Magris, Lara,More O'Ferrall, Rory A.
, p. 784 - 795 (2002)
The equilibrium constant for keto-phenol tautomerisation of anthrone to 9-anthrol (KE = [phenol]/[ketone]) has been determined as pKE (-log KE) = 2.10 from ratios of rate constants for ketonisation of anthrol and phenolisation of anthrone in aqueous acetic acid buffers at 253°C. Combining this value with pKa = 10.0 for the ionization of anthrone, measured spectrophotometrically in piperazine and borate buffers, gives pKa = 7.9 for the phenolic hydroxy group of anthrol. Measurements of rate constants for tautomerisation showed acid catalysis by H3O+ in aqueous HCl but by the base component only in buffer solutions of weaker acids. The H3O+-catalysed reaction is subject to a solvent isotope effect kH3O/kD3O = 4.8, consistent with protonation of 9-anthrol at the 10-carbon atom of the anthracene ring in the rate-determining step. Comparison with hydrolysis of the methyl ether of anthrol showed that ketonisation is faster by a factor of 3000. This large rate difference is consistent with NMR measurements which show that deuterium isotope exchange at the 10-position of the anthryl methyl ether occurs in competition with hydrolysis. This accounts for a 60-70 fold of the rate difference. The residue is attributed to (a) a normal difference of 16-fold in protonation rates of phenols and the corresponding methyl ethers and (b) a minor contribution from steric hindrance to resonance stabilisation of the anthracen-9-onium ion intermediate in the hydrolysis reaction from interaction of the conjugating methoxy group with the 1,8-hydrogen atoms of the adjacent phenyl rings.
g-C3N4/metal halide perovskite composites as photocatalysts for singlet oxygen generation processes for the preparation of various oxidized synthons
Corti, Marco,Chiara, Rossella,Romani, Lidia,Mannucci, Barbara,Malavasi, Lorenzo,Quadrelli, Paolo
, p. 2292 - 2298 (2021/04/12)
g-C3N4/metal halide perovskite composites were prepared and used for the first time as photocatalysts forin situ1O2generation to perform hetero Diels-Alder, ene and oxidation reactions with suitable dienes and alkenes. The standardized methodology was made applicable to a variety of olefinic substrates. The scope of the method is finely illustrated and the reactions afforded desymmetrized hydroxy-ketone derivatives, unsaturated ketones and epoxides. Some limitations were also observed, especially in the case of the alkene oxidations, and poor chemoselectivity was somewhere observed in this work which is the first application of MHP-based composites forin situ1O2generation. The experimental protocol can be used as a platform to further expand the knowledge and applicability of MHPs to organic reactions, since perovskites offer a rich variety of tuning strategies which may be explored to improve reaction yields and selectivities.
Insight into the chemoselective aromatic: Vs. side-chain hydroxylation of alkylaromatics with H2O2catalyzed by a non-heme imine-based iron complex
Ticconi, Barbara,Capocasa, Giorgio,Cerrato, Andrea,Di Stefano, Stefano,Lapi, Andrea,Marincioni, Beatrice,Olivo, Giorgio,Lanzalunga, Osvaldo
, p. 171 - 178 (2021/01/28)
The oxidation of a series of alkylaromatic compounds with H2O2 catalyzed by an imine-based non-heme iron complex prepared in situ by reaction of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 in a 2?:?2?:?1 ratio leads to a marked chemoselectivity for aromatic ring hydroxylation over side-chain oxidation. This selectivity is herein investigated in detail. Side-chain/ring oxygenated product ratio was found to increase upon decreasing the bond dissociation energy (BDE) of the benzylic C-H bond in line with expectation. Evidence for competitive reactions leading either to aromatic hydroxylation via electrophilic aromatic substitution or side-chain oxidation via benzylic hydrogen atom abstraction, promoted by a metal-based oxidant, has been provided by kinetic isotope effect analysis. This journal is
Ligand-Constraint-Induced Peroxide Activation for Electrophilic Reactivity
Ansari, Mursaleem,Chandra, Anirban,Kundu, Subrata,Monte-Pérez, Inés,Rajaraman, Gopalan,Ray, Kallol
supporting information, p. 14954 - 14959 (2021/06/01)
μ-1,2-peroxo-bridged diiron(III) intermediates P are proposed as reactive intermediates in various biological oxidation reactions. In sMMO, P acts as an electrophile, and performs hydrogen atom and oxygen atom transfers to electron-rich substrates. In cyanobacterial ADO, however, P is postulated to react by nucleophilic attack on electrophilic carbon atoms. In biomimetic studies, the ability of μ-1,2-peroxo-bridged dimetal complexes of Fe, Co, Ni and Cu to act as nucleophiles that effect deformylation of aldehydes is documented. By performing reactivity and theoretical studies on an end-on μ-1,2-peroxodicobalt(III) complex 1 involving a non-heme ligand system, L1, supported on a Sn6O6 stannoxane core, we now show that a peroxo-bridged dimetal complex can also be a reactive electrophile. The observed electrophilic chemistry, which is induced by the constraints provided by the Sn6O6 core, represents a new domain for metal?peroxide reactivity.
V2O5@TiO2 Catalyzed Green and Selective Oxidation of Alcohols, Alkylbenzenes and Styrenes to Carbonyls
Upadhyay, Rahul,Kumar, Shashi,Maurya, Sushil K.
, p. 3594 - 3600 (2021/07/02)
The versatile application of different functional groups such as alcohols (1° and 2°), alkyl arenes, and (aryl)olefins to construct carbon-oxygen bond via oxidation is an area of intense research. Here, we report a reusable heterogeneous V2O5@TiO2 catalyzed selective oxidation of various functionalities utilizing different mild and eco-compatible oxidants under greener reaction conditions. The method was successfully applied for the alcohol oxidation, oxidative scission of styrenes, and benzylic C?H oxidation to their corresponding aldehydes and ketones. The utilization of mild and eco-friendly oxidizing reagents such as K2S2O8, H2O2 (30 % aq.), TBHP (70 % aq.), broad substrate scope, gram-scale synthesis, and catalyst recyclability are notable features of the developed protocol.
A Synthetic Model for the Possible FeIV2(μ-O)2Core of Methane Monooxygenase Intermediate Q Derived from a Structurally Characterized FeIIIFeIV(μ-O)2Complex
Aono, Yuri,Harada, Masafumi,Kajiwara, Atsushi,Katano, Hajime,Kobayashi, Yoshio,Kodera, Masahito,Kotegawa, Fukue,Kubo, Minoru,Matsumoto, Arimasa,Mikata, Yuji,Nakayama, Hiromi,Yamamoto, Chihiro,Yanagisawa, Sachiko
supporting information, (2021/12/09)
A bis(μ-oxo)diiron(IV,IV) complex as a model for intermediate Q in the methane monooxygenase reaction cycle has been prepared. The precursor complex with a [FeIIIFeIV(μ-O)2] core was fully characterized by X-ray crystallography and other spectroscopic analyses and was converted to the [FeIV2(μ-O)2] complex via electrochemical oxidation at 1000 mV (vs Ag/Ag+) in acetone at 193 K. The UV-vis spectral features, M?ssbauer parameters (ΔEQ = 2.079 mm/s and δ= -0.027 mm/s), and EXAFS analysis (Fe-O/N = 1.73/1.96 ? and Fe···Fe = 2.76 ?) support the structure of the low-spin (S = 1, for each Fe) [FeIV2(μ-O)2] core. The rate constants of the hydrogen abstraction reaction from 9,10-dihydroanthracene at 243 K suggest the high reactivity of these synthetic bis(μ-oxo)diiron complexes supported by simple N4 tripodal ligand.
Visible-Light-Triggered Quantitative Oxidation of 9,10-Dihydroanthracene to Anthraquinone by O2 under Mild Conditions
Jiang, Dabo,Hu, Wenwei,Chen, Mengke,Fu, Zaihui,Su, Anqun,Yang, Bo,Mao, Feng,Zhang, Chao,Liu, Yachun,Yin, Dulin
, p. 1785 - 1792 (2020/03/13)
The development of mild and efficient processes for the selective oxygenation of organic compounds by molecular oxygen (O2) is key for the synthesis of oxygenates. This paper discloses an atom-efficient synthesis protocol for the photo-oxygenation of 9,10-dihydroanthracene (DHA) by O2 to anthraquinone (AQ), which could achieve quantitative AQ yield (100 %) without any extra catalysts or additives under ambient temperature and pressure. A yield of 86.4 % AQ was obtained even in an air atmosphere. Furthermore, this protocol showed good compatibility for the photo-oxidation of several other compounds with similar structures to DHA. From a series of control experiments, free-radical quenching, and electron paramagnetic resonance spin-trapping results, the photo-oxygenation of DHA was probably initiated by its photoexcited state DHA*, and the latter could activate O2 to a superoxide anion radical (O2.?) through the transfer of its electron. Subsequently, this photo-oxidation was gradually dominated by the oxygenated product AQ as an active photocatalyst obtained from the oxidation of DHA by O2.?, and was accelerated with the rapid accumulation of AQ. The present photo-oxidation protocol is a good example of selective oxygenation based on the photoexcited substrate self-activated O2, which complies well with green chemistry ideals.
Fast Hydrocarbon Oxidation by a High-Valent Nickel–Fluoride Complex
Lovisari, Marta,McDonald, Aidan R.,Mondal, Prasenjit,Twamley, Brendan
supporting information, p. 13044 - 13050 (2020/06/05)
In the search for highly reactive oxidants we have identified high-valent metal–fluorides as a potential potent oxidant. The high-valent Ni–F complex [NiIII(F)(L)] (2, L=N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate) was prepared from [NiII(F)(L)]? (1) by oxidation with selectfluor. Complexes 1 and 2 were characterized by using 1H/19F NMR, UV-vis, and EPR spectroscopies, mass spectrometry, and X-ray crystallography. Complex 2 was found to be a highly reactive oxidant in the oxidation of hydrocarbons. Kinetic data and products analysis demonstrate a hydrogen atom transfer mechanism of oxidation. The rate constant determined for the oxidation of 9,10-dihydroanthracene (k2=29 m?1 s?1) compared favorably with the most reactive high-valent metallo-oxidants. Complex 2 displayed reaction rates 2000–4500-fold enhanced with respect to [NiIII(Cl)(L)] and also displayed high kinetic isotope effect values. Oxidative hydrocarbon and phosphine fluorination was achieved. Our results provide an interesting direction in designing catalysts for hydrocarbon oxidation and fluorination.
On/Off O2 Switchable Photocatalytic Oxidative and Protodecarboxylation of Carboxylic Acids
Bazyar, Zahra,Hosseini-Sarvari, Mona
, p. 13503 - 13515 (2019/10/11)
Photoredox catalysis in recent years has manifested a powerful branch of science in organic synthesis. Although merging photoredox and metal catalysts has been a widely used method, switchable heterogeneous photoredox catalysis has rarely been considered. Herein, we open a new window to use a switchable heterogeneous photoredox catalyst which could be turned on/off by changing a simple stimulus (O2) for two opponent reactions, namely, oxidative and protodecarboxylation. Using this strategy, we demonstrate that Au@ZnO core-shell nanoparticles could be used as a switchable photocatalyst which has good catalytic activity to absorb visible light due to the localized surface plasmon resonance effect of gold, can decarboxylate a wide range of aromatic and aliphatic carboxylic acids, have multiple reusability, and are a reasonable candidate for synthesizing both aldehydes/ketones and alkane/arenes in a large-scale set up. Some biologically active molecules are also shown via examples of the direct oxidative and protodecarboxylation which widely provided pharmaceutical agents.
