- Magnetic Field Effects on the Catalytic Oxidation of 2,6-Di-tert-butylphenol by CoSMDPT: 2H and 17O Magnetic Isotope Effects
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The effect of a magnetic field between 0 and 70 kG on the catalytic oxidation rate of 2,6-di-tert-butylphenol, DTBP, to form 2,6-di-tert-butylquinone, BQ, by cobalt(II) bis(3-(salicylideneamino)propyl)methylamine, CoSMDPT, in the presence of O2 is reported.No kinetic 2H isotope effect is observed with DTBP-OD, and DTBP-4-d1-OD exhibits mass and magnetic kinetic isotope effects of 1.25 and 1.22, respectively.In the presence of additive phenol, CoSMDPT catalyzes the formation of 2,2',6,6'-tetra-tert-butyldiphenoquinone, DPQ.The mass and magnetic isotope effects in DPQ formation are negligible for the deuteration of the phenolic position.DTBP-4-d1-OD in the presence of phenol-OD exhibits kinetic mass and magnetic 2H isotope effects in DPQ formation of 1.73 and 1.31, respectively.These results are compared to the oxidation rate of DTBP by Pb(OAc)4, which is unaffected by a 0-70-kG magnetic field and has a 2H kinetic isotope effect of 1.28 for DTBP-4-d1-OD.A significant 17O magnetic isotope effect is observed only for BQ production.The 17O enrichment of BQ given has an overall enrichment factor, S(f)=1.76, at 9percent DTBP conversion.These results are discussed in terms of a proposed mechanism.
- Perito, Richard P.,Corden, Barry B.
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- Structure, Spectroscopy, and Reactivity of a Mononuclear Copper Hydroxide Complex in Three Molecular Oxidation States
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Structural, spectroscopic, and reactivity studies are presented for an electron transfer series of copper hydroxide complexes supported by a tridentate redox-active ligand. Single crystal X-ray crystallography shows that the mononuclear [CuOH]1+ core is stabilized via intramolecular H-bonds between the H-donors of the ligand and the hydroxide anion when the ligand is in its trianionic form. This complex undergoes two reversible oxidation processes that produce two metastable "high-valent"CuOH species, which can be generated by addition of stoichiometric amounts of 1e- oxidants. These CuOH species are characterized by an array of spectroscopic techniques including UV-vis absorption, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies (XAS), which together indicate that all redox couples are ligand-localized. The reactivity of the complexes in their higher oxidation states toward substrates with modest O-H bond dissociation energies (e.g., 4-substitued-2,6-di-tert-butylphenols) indicates that these complexes act as 2H+/2e- oxidants, differing from the 1H+/1e- reactivity of well-studied [CuOH]2+ systems.
- Garcia-Bosch, Isaac,Lancaster, Kyle M.,Macmillan, Samantha N.,Rajabimoghadam, Khashayar,Siegler, Maxime A.,Wu, Tong
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- Novel photochemical coupling of hindered phenols in the presence of acridine mechanistically probed by CIDEP
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Irradiation of hindered phenols in the presence of acridine as a light absorber gives bisphenols and biacridane.CIDEP study establishes the path of hydrogen abstraction by the triplet acridine.The overall mechanism is proposed by the product analysis and the CIDEP studies.
- Okada, Keiji,Okubo, Katsura,Oda, Masaji,Murai, Hisano
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- Performance of 4,4'-Bis(2,6-di-tert-butylphenol) in stabilization of isoprene rubber and polypropylene
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The antioxidant performance of a sterically hindered bisphenol antioxidant, 4,4'-bis(2,6-di-tert-butylphenol), in model reactions of accelerated aging of carbon-chain polymers (polypropylene, isoprene rubber) was studied. This antioxidant was examined by differential scanning calorimetry and Wallace plasticity measurements in comparison with known commercial phenolic and amine stabilizers. High performance of 4,4'-bis(2,6-di-tert-butylphenol) as antioxidant was revealed.
- Akhmadullin,Gatiyatullin,Vasil'Ev,Akhmadullina,Mukmeneva,Cherezova,Yang, Mingshu
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- Liquid-phase oxidation of 2,6-di-tert-butylphenol with Cu-impregnated MCM-41 catalysts in the presence of alkali metals
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Mesoporous silicate MCM-41, with a uniform pore diameter of ca. 35 A, was used as a support for impregnated Cu catalysts for liquid-phase oxidation of 2,6-di-tert-butylphenol (BOH) in the presence of a base such as KOH. The oxidation products were 4,4′-dihydroxy-3,3′,5,5′-tetra-tert-butyl-biphenyl (H2DPQ) and 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone (DPQ). An alkali such as a potassium salt, which promotes the phenol oxidation activity of copper ion-impregnated MCM-41 (Cu/MCM-41) catalyst, was found to be more effective as an additive to the reaction solution than impregnation on the Cu/MCM-41 catalyst. The added alkali was found to play a role in generating the corresponding phenolate anion by dissolving a BOH molecule. H2DPQ is formed through tautomerization of an intermediate dimer obtained by the C-C coupling of the corresponding phenoxy radicals. DPQ is formed via the consecutive oxidation of H2DPQ and/or via the oxidative dehydrogenation of the intermediate dimer. The BOH molecules in the mesopores of Cu/MCM-41, rather than the BOH in bulk solution in the presence of CuCl2, were found to favor H2DPQ production. Cu/MCM-41 with added potassium [(K-Cu)/MCM-41] was much more active for phenol oxidation than Cu-impregnated NaZSM-5 with added potassium [(K-Cu)/NaZSM-5] or the corresponding NaY [(K-Cu)/NaY], each catalyst having only uniform micropores. This result indicates that the oxidation of sterically bulky BOH occurs mainly at the active sites in the mesopores and is difficult to carry out in the micropores of (K-Cu)/NaZSM-5 and (K-Cu)/NaY zeolites because of the steric bulkiness of the oxidation products, H2DPQ and DPQ. The liquid-phase adsorption amounts of BOH on NaZSM-5 and NaY were found to be comparable to that on MCM-41. The shape selectivity by the oxidation products in the micropores of (K-Cu)/NaZSM-5 and (K-Cu)/NaY zeolites was thus suggested to inhibit the BOH oxidation activities of both catalysts, based on the results of the oxidation reaction and liquid-phase adsorption of BOH.
- Fujiyama, Hirofumi,Kohara, Ichitaro,Iwai, Keisuke,Nishiyama, Satoru,Tsuruya, Shigeru,Masai, Mitsuo
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- Electrooxidative Coupling of Phenols. I. Product-Selective Electrosynthesis of 2,2',6,6'-Tetra-tert-butyl-1,1'-biphenol from 2,6-Di-tert-butylphenol
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Biphenol electrosynthesis is achieved in a divided cell by a set of redox reactions from 2,6-di-tert-butylphenol (4) via the corresponding diphenoquinone 3.Phenol 4 can also lead to either the corresponding biphenol 2 or diphenoquinone 3 in a product-selective manner by electrooxidation in an undivided cell.The choice of solvent is a crucial factor for the product-selectivity.
- Torii, Sigeru,Dhimane, Anne-Lise,Araki, Yoshitaka,Inokuchi, Tsutomu
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- Antibacterial activity of dipropofol and related compounds
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Phenolic compounds, in general, exhibit antioxidant and antibacterial activities. We studied antimicrobial activity of the phenolic antioxidants, propofol (2,6-diisopropylphenol), tocopherol, eugenol, butylated hydroxyanisole (BHA), and several of their dimer compounds. Dipropofol (dimer of 2,6-diisopropylphenol) showed strong antibacterial activity against gram-positive strains including methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococci (VRE), while propofol and other monomeric and dimeric phenols having methyl or tert-butyl groups showed no remarkable activity. The results indicated that the dimeric structure of 2,6-diisopropylphenol moiety may play an important role in the antibacterial activity.
- Ogata, Masahiro,Sato, Kanae Tutumimoto,Kunikane, Takao,Oka, Kentaro,Seki, Masako,Urano, Shiro,Hiramatsu, Keiichi,Endo, Toyoshige
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- Reduction of 4,4′-stilbenequinone and 4,4′-diphenoquinone upon reaction with photogenerated radicals
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The properties of 3,3′,5,5′-tetra-tert-butyl-4,4′- stilbenequinone (StQ) were studied by photochemical means. Acetone, acetophenone or benzophenone was photolyzed in the presence of both StQ and a donor, such as alcohols or triethylamine. This initiated reaction of a ketyl radical with StQ to form a semiquinone radical and eventually induce a permanent bleaching due to conversion of StQ to 4,4′-dihydroxystilbene (StQH2). The quantum yield of conversion of StQ to StQH2 increases with the donor concentration. Similar effects were found for the ketone-sensitized radical-induced conversions of the analogous diphenoquinone to the reduction product, diphenol.
- Goerner, Helmut
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- (Nitrosonaphtholato)metal complex-catalyzed oxidation of phenols and alkenes
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Bis(1-nitroso-2-naphtholato)manganese(II), tris(1-nitroso-2-naphtholato)manganese(III), tris(2-nitroso-1-naphtholato)manganese(III), bis(1-nitroso-2-naphtholato)cobalt(II), bis(1-nitroso-2-naphtholato)nickel(II), bis(1-nitroso-2-naphtholato)copper(II) and bis(1-nitroso-2-naphtholato)zinc(II) were prepared and their catalytic abilities in the oxidation of phenols were examined. The best yields of diphenoquinones were obtained when the catalytic oxidation using bis(1-nitroso-2-naphtholato)manganese(II) was carried out at 23°C under an oxygen atmosphere (1 atm) in the presence of a phosphine ligand. Likewise, phenols were completely converted to the corresponding diphenoquinones together with small amounts of benzoquinones under an oxygen pressure (20 atm) at 50°C in a short period of time. It was proven that the manganese(II) catalyst, molecular oxygen, and phosphine ligand were essential for the catalytic phenol oxidation. On the other hand. bis(1-nitroso-2-naphtholato)manganese(II)-catalyzed epoxidation of alkenes was only effective when iodosylbenzene was used. The catalytic oxidation mechanism was discussed on the basis of the measurement of cyclic voltammograms of the (nitrosonaphtholato)metal complexes, isolated intermediates, and effect of additives.
- Nishino, Hiroshi,Satoh, Hideaki,Yamashita, Mayumi,Kurosawa, Kazu
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- Clean synthesis of 3,3′,5,5′-Tetra-tert-butyl-4,4′-diphenoquinone from the oxidative coupling of 2,6-Di-tert-butylphenol catalyzed by alkali-promoted Cu-Mg-Al hydrotalcites in the presence of molecular oxygen
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2,6-Di-tert-butylphenol is selectively transformed to 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone in the presence of molecular oxygen using alkali-promoted Cu-Mg-Al hydrotalcites as recyclable heterogeneous catalysts.
- Iwai, Keisuke,Yamauchi, Takayoshi,Hashimoto, Keiji,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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- Chromium-Salen Catalyzed Cross-Coupling of Phenols: Mechanism and Origin of the Selectivity
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A highly chemoselective phenol cross-coupling reaction catalyzed by a Cr-salen catalyst was developed. Kinetic studies showed that the oxidation of Cr(III) to Cr(V) is the rate-determining step of the reaction. In addition, experimental stoichiometric analysis showed that a high valent Cr(V) species is the active catalyst for this process. The selectivity of the reaction was found to be determined by the cross-coupling carbon-carbon bond forming reaction, rather than any precoordination species. It appears that the lowest energy cross-coupling pathway requires a lesser degree of electronic reorganization in its transition state vs the lowest energy homocoupling pathway. This result was supported by stoichiometric Cr(V) kinetics, 13C kinetic isotope effects, and density functional theory (DFT) calculations. The understanding of the full landscape of this reaction allowed us to develop a general analysis to predict the regioselectivity of the cross-coupling reaction.
- Nieves-Quinones, Yexenia,Paniak, Thomas J.,Lee, Young Eun,Kim, Sun Min,Tcyrulnikov, Sergei,Kozlowski, Marisa C.
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- Carbonic anhydrase inhibitors. Inhibition of human erythrocyte isozymes I and II with a series of antioxidant phenols
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The inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II, with a series of phenol derivatives was investigated by using the esterase assay, with 4-nitrophenyl acetate as substrate. 2,6-Dimethylphenol, 2,6-diisopropylphenol (propofol), 2,6-di-t-butylphenol, butylated hydroxytoluene, butylated hydroxyanisole, vanillin, guaiacol, di(2,6-dimethylphenol), di(2,6-diisopropylphenol), di(2,6-di-t-butylphenol), and acetazolamide showed KI values in the range of 37.5-274.5 μM for hCA I and of 0.29-113.5 μM against hCA II, respectively. All these phenols were non-competitive inhibitors with 4-nitrophenylacetate as substrate. Some antioxidant phenol derivatives investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms which have not been yet assayed for their interactions with such agents.
- Sentuerk, Murat,Guelcin, Ilhami,Dastan, Arif,Irfan Kuefrevioglu, Oe.,Supuran, Claudiu T.
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- On the Structures of the Intermediates from Reversible Coupling between Hindered Phenoxy Radicals
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Hindered phenoxy radicals 1 and 2 are found to undergo reversible, C-C rather than C-O cross-coupling, and give bis(cyclohexadienone)s 14 and 17.These primary products are not isolable but are recovered as phenolic cyclohexadienones 15 and 18, respectively, after treatment with Et3N or as biphenols 16 and 12, respectively, after treatment with TFA.The other products obtained after treating the reaction mixture with Et3N or TFA are phenol 5 and 4,4'-diphenoquinone 13 alone.Dienones 14 and 17 are interconvertible with each other via dissociation into the parent radicals, and 14 appears to be thermodynamically more stable than 17.Phenoxy radical 1 and other, less hindered 2,6-dialkylphenoxy radicals 24 also form intermediates of reversible cross-coupling.Treatment with TFA of the mixtures containing the intermediates provides 2,4'-biphenols 25 preferentially.
- Omura, Kanji
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- Catalytic oxidation of hindered phenols by a copper(I) complex and dioxygen
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The dioxygen reaction product of a binuclear copper(I) complex of a new m-xylyl-based ligand has proven to be a catalyst in the promotion of oxidative carbon-carbon coupling of hindered phenols, which leads to bisphenol and diphenoquinones. (C) 2000 Elsevier Science Ltd.
- Gupta,Mukherjee
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- Antioxidant activity of propofol and related monomeric and dimeric compounds
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This study was carried out to investigate the antioxidant activity of propofol (2,6-diisopropylphenol) and its related compounds, butylated hydroxyanisole (BHA), 2,6-dimethylphenol, 2,6-di-t-butylphenol, and their dimeric compounds. The degree of antioxidant activity was evaluated based on the degree of peroxidation induced with Fe-ascorbic acid in egg phosphatidylcholine through the determination of thiobarbituric acid-reactive substances (TBARS) formed during peroxidation. Their antioxidant activities were in the order of dipropofol>di(2,6-di-t-butylphenol)>diBHA>di(2,6-dimethylphenol). Dipropofol, a dimeric compound of propofol, showed the highest antioxidant activities. Dimeric compounds had higher activities than monomeric compounds, and the 1,1-diphenyl-p-picryhydrazyl-trapping ability of dimeric compounds was also greater than those of monomeric compounds (4-10-fold). These results suggest that dimeric phenols may increase their antioxidant activities along with increments in the conjugation system and play a inhibitory role in the propagation of free radical chain reactions.
- Ogata, Masahiro,Shin-Ya, Kazuo,Urano, Shiro,Endo, Toyoshige
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- Oxidation of 2,6-di-tert-butylphenol by tetrapyridyl oxoiron(IV) complex
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The reactivity of the previously reported pentadentate low-spin (S = 1) oxoiron(IV) complex, [FeIV(O)(asN4Py)] (2) (asN4Py = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine), has been investigated in the oxidation reaction of 2,6-di-tert-butylphenol derivatives. Detailed kinetic, and mechanistic studies (kinetic isotope effect (KIE) of 4.52, and Hammett correlation with ρ = ?1.83), lead to the conclusion that the rate-determining step in this reaction involves direct hydrogen-atom transfer (HAT) from the phenol by the oxoiron(IV) species, in contrast to the heme-type horseradish peroxidase (HRP) system.
- Lakk-Bogáth, Dóra,Speier, Gábor,Kaizer, József
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- Selective Formation of 4,4′-Biphenols by Anodic Dehydrogenative Cross- and Homo-Coupling Reaction
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A simple and selective electrochemical synthesis by dehydrogenative coupling of unprotected 2,6- or 2,5-substituted phenols to the desired 4,4′-biphenols is reported. Using electricity as the oxidizing reagent avoids pre-functionalization of the starting materials, since a selective activation of the substrates takes place. Without the necessity for metal-catalysts or the use of stoichiometric reagents it is an economic and environmentally friendly transformation. The elaborated electrochemical protocol leads to a broad variety of the desired 4,4′-biphenols in a very simplified manner compared to classical approaches. This is particular the case for the cross-coupled products.
- Dahms, Benedikt,Kohlpaintner, Philipp J.,Wiebe, Anton,Breinbauer, Rolf,Schollmeyer, Dieter,Waldvogel, Siegfried R.
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- A dual-functional heterogeneous ruthenium catalyst for the green one-pot synthesis of biphenols
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A green one-pot synthesis of biphenols using O2 and H2 was achieved using a magadiite-supported Ru nanoparticle catalyst. This catalyst selectively promoted the oxidative coupling of phenols to diphenoquinones with O2, followed by the successive reduction of these diphenoquinones to biphenols using H2 in a single reactor.
- Maeno, Zen,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro
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- Reactivity of iPrPCPIrH4 with para-benzoquinones
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In the interest of investigating new hydrogen acceptors for pincer–iridium catalyzed dehydrogenations with the ability to be catalytically recycled, a series of para-benzoquinones have been reacted with iPrPCPIrH4 in various solvents and conditions. Preliminary results indicate that a wide range of quinones are capable of dehydrogenating iPrPCPIrH4, and that several turn-overs in alcohol dehydrogenation by iPrPCPIr are possible at room temperature using benzoquinone acceptors. However, strong acceptor–catalyst interactions are inhibitory toward catalysis when the acceptor is used in excess. A new class of (bis)-η2 pi-adducts, formed between iPrPCPIr and benzoquinones, nicknamed “barber-chairs”, has been identified and 3 examples have been characterized.
- Wilklow-Marnell, Miles,Brennessel, William W.,Jones, William D.
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- Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center
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In soluble methane monooxygenase enzymes (sMMO), dioxygen (O2) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono-or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, 1-trans, that activates O2 to form the corresponding iron(IV)-oxo complex, 2-trans, via a mechanism reminiscent of the O2 activation process in sMMO. The conversion of 1-trans to 2-trans proceeds via the intermediate formation of an iron(III)-superoxide species 3, which could be trapped and spectroscopically characterized at-50 °C. Surprisingly, 3 is a stronger oxygen atom transfer (OAT) agent than 2-trans; 3 performs OAT to 1-trans or PPh3 to yield 2-trans quantitatively. Furthermore, 2-trans oxidizes the aromatic C-H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3, represents new domains of oxoiron(IV) and superoxoiron(III) reactivities.
- Kass, Dustin,Corona, Teresa,Warm, Katrin,Braun-Cula, Beatrice,Kuhlmann, Uwe,Bill, Eckhard,Mebs, Stefan,Swart, Marcel,Dau, Holger,Haumann, Michael,Hildebrandt, Peter,Ray, Kallol
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supporting information
p. 5924 - 5928
(2020/05/08)
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- Chromium-Salen Catalyzed Cross-Coupling of Phenols: Mechanism and Origin of the Selectivity
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A highly chemoselective phenol cross-coupling reaction catalyzed by a Cr-salen catalyst was developed. Kinetic studies showed that the oxidation of Cr(III) to Cr(V) is the rate-determining step of the reaction. In addition, experimental stoichiometric analysis showed that a high valent Cr(V) species is the active catalyst for this process. The selectivity of the reaction was found to be determined by the cross-coupling carbon-carbon bond forming reaction, rather than any precoordination species. It appears that the lowest energy cross-coupling pathway requires a lesser degree of electronic reorganization in its transition state vs the lowest energy homocoupling pathway. This result was supported by stoichiometric Cr(V) kinetics, 13C kinetic isotope effects, and density functional theory (DFT) calculations. The understanding of the full landscape of this reaction allowed us to develop a general analysis to predict the regioselectivity of the cross-coupling reaction.
- Nieves-Quinones, Yexenia,Paniak, Thomas J.,Lee, Young Eun,Kim, Sun Min,Tcyrulnikov, Sergei,Kozlowski, Marisa C.
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supporting information
p. 10016 - 10032
(2019/07/04)
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- Catalytic Aerobic Phenol Homo- and Cross-Coupling Reactions with Copper Complexes Bearing Redox-Active Guanidine Ligands
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Due to their large importance in synthetic chemistry, catalytic C?C coupling reactions of phenols are currently intensively studied. Herein, new copper catalysts for the C?C coupling reaction of phenols using dioxygen as a green oxidizing reagent are reported. By using redox-active guanidine ligands, the activity as well as chemoselectivity in the cross-coupling reaction of non-complementary phenols (between an electron-rich phenol and a less nucleophilic second phenol) is significantly improved. Based on the collected data for several test reactions, a reaction mechanism is proposed.
- Sch?n, Florian,Kaifer, Elisabeth,Himmel, Hans-J?rg
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supporting information
p. 8279 - 8288
(2019/06/04)
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- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Pd-Catalyzed Aerobic Oxidation Reactions: Strategies to Increase Catalyst Lifetimes
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The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.
- Ho, Wilson C.,Chung, Kevin,Ingram, Andrew J.,Waymouth, Robert M.
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supporting information
p. 748 - 757
(2018/01/26)
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- Industrialized synthesis method of high-purity biphenyl diphenol compound
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The invention discloses an industrialized synthesis method of a high-purity biphenyl diphenol compound. The synthesis method comprises the steps that a phenolic compound A of which the ortho-position or para-position is a hydrogen atom serves as the raw material, alkali metal hydroxide or alkaline earth metal hydroxide or weak-acid alkali metal salt serves as a catalyst, different phenolic compounds are added to serve as oxidation regulators, all the substances are mixed and heated to 65 DEG C-185 DEG C, and meanwhile oxygen or air is blown into the mixture for an oxidation coupling reaction; after the PH value of the reaction system is adjusted through an acidic substance, a disproportionated reaction is conducted in an inert gas environment at the temperature ranging from 65 DEG C to 245 DEG C, and the high-purity biphenyl diphenol compound B or C is obtained. According to the preparation method of the high-purity biphenyl diphenol compound, the steps are simple, the reaction conditions are mild, the cost is low, the reaction materials can be recycled, the product is good in color, the product purity reaches up to 99.9 percent, and the preparation method is very suitable for industrialized production.
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Paragraph 0029; 0030
(2016/11/14)
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- Industrial preparation method of biphenol compounds with high purity
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The invention discloses an industrial preparation method of biphenol compounds with high purity. The preparation method comprises the following steps: (1) a phenolic compound A containing a tert-butyl group whose ortho-position or para-position is a hydrogen atom is used as a raw material, an oxidative coupling reaction and a disproportionation reaction are carried out, and a tert-butyl-containing 4,4'-biphenol or 2,2'-biphenol compound is obtained; (2) a de-tert-butylation reaction is carried out for the tert-butyl-containing 4,4'-biphenol or 2,2'-biphenol compound at 100-220 DEG C with a strongly acidic catalyst in phenols or aliphatic solvents with high-boiling point, and a 4,4'-biphenol compound B or a 2,2'-biphenol compound C with high-purity is obtained. The preparation method of the 4,4'-biphenol or 2,2'-biphenol compound has the advantages of simple steps, mild reaction condition, low cost, cyclic utilization of reaction raw materials, excellent color of the product and high yield; the purity of the product reaches 99.9%, and the method is suitable for industrial production.
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Paragraph 0024-0025
(2017/03/14)
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- Tuning the Reactivity of Terminal Nickel(III)-Oxygen Adducts for C-H Bond Activation
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Two metastable NiIII complexes, [NiIII(OAc)(L)] and [NiIII(ONO2)(L)] (L = N,N′-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamidate, OAc = acetate), were prepared, adding to the previously prepared [NiIII(OCO2H)(L)], with the purpose of probing the properties of terminal late-transition metal oxidants. These high-valent oxidants were prepared by the one-electron oxidation of their NiII precursors ([NiII(OAc)(L)]- and [NiII(ONO2)(L)]-) with tris(4-bromophenyl)ammoniumyl hexachloroantimonate. Fascinatingly, the reaction between any [NiII(X)(L)]- and NaOCl/acetic acid (AcOH) or cerium ammonium nitrate ((NH4)2[CeIV(NO3)6], CAN), yielded [NiIII(OAc)(L)] and [NiIII(ONO2)(L)], respectively. An array of spectroscopic characterizations (electronic absorption, electron paramagnetic resonance, X-ray absorption spectroscopies), electrochemical methods, and computational predictions (density functional theory) have been used to determine the structural, electronic, and magnetic properties of these highly reactive metastable oxidants. The NiIII-oxidants proved competent in the oxidation of phenols (weak O-H bonds) and a series of hydrocarbon substrates (some with strong C-H bonds). Kinetic investigation of the reactions with di-tert-butylphenols showed a 15-fold enhanced reaction rate for [NiIII(ONO2)(L)] compared to [NiIII(OCO2H)(L)] and [NiIII(OAc)(L)], demonstrating the effect of electron-deficiency of the O-ligand on oxidizing power. The oxidation of a series of hydrocarbons by [NiIII(OAc)(L)] was further examined. A linear correlation between the rate constant and the bond dissociation energy of the C-H bonds in the substrates was indicative of a hydrogen atom transfer mechanism. The reaction rate with dihydroanthracene (k2 = 8.1 M-1 s-1) compared favorably with the most reactive high-valent metal-oxidants, and showcases the exceptional reactivity of late transition metal-oxygen adducts.
- Pirovano, Paolo,Farquhar, Erik R.,Swart, Marcel,McDonald, Aidan R.
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supporting information
p. 14362 - 14370
(2016/11/13)
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- Changing the chemical and physical properties of high valent heterobimetallic bis-(μ-oxido) Cu-Ni complexes by ligand effects
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Two new heterobimetallic [LNiO2Cu(RPY2)]+ (RPY2 = N-substituted bis 2-pyridyl(ethylamine) ligands with R = indane, 3a or R = Me, 3b) complexes have been spectroscopically trapped at low temperatures. They were prepared by reacting the mononuclear side-on LNiII superoxo precursor bearing a β-diketiminate ligand (L = [HC-(CMeNC6H3(iPr)2)2]) with the Cu(i) complexes. In contrast to the oxo groups in known high-valent [M2(μ-O)2]n+ (M = Fe, Co, Ni, Cu) cores that display electrophilic reactivities, 3a and 3b display rather nucleophilic oxo cores active in aldehyde deformylation reactions. However, the spectroscopic and reactivity properties of 3a/3b are found to be distinct relative to that of the previously reported [LNiO2Cu(MeAN)]+ complex containing a more basic (nucleophilic) N,N,N′,N′,N′-pentamethyl-dipropylenetriamine (MeAN) ligand at the copper centre. The geometry and electronic properties of the copper ligands affect the electron density of the oxygen atoms of the heterodinuclear {Ni(μ-O)2} core and 3a/3b undergo slower nucleophilic and faster electrophilic reactions than the previously reported [LNiO2Cu(MeAN)]+ intermediate. The present study therefore demonstrates the tuning of the electrophilicity/nucleophilicity of the oxygen atoms of the heterobimetallic [Ni(μ-O)2Cu]2+ cores by controlling the electron donation from the ancillary ligands, and underlines the significance of subtle electronic changes in the physical and chemical properties of the biologically relevant heterobimetallic metal-dioxygen intermediates.
- Kafentzi, Maria-Chrysanthi,Orio, Maylis,Réglier, Marius,Yao, Shenglai,Kuhlmann, Uwe,Hildebrandt, Peter,Driess, Matthias,Simaan, A. Jalila,Ray, Kallol
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supporting information
p. 15994 - 16000
(2016/10/22)
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- Selective oxidative homo-and cross-coupling of phenols with aerobic catalysts
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Simple catalysts that use atom-economical oxygen as the terminal oxidant to accomplish selective ortho-ortho, ortho-para, or para-para homo-couplings of phenols are described. In addition, chromium salen catalysts have been discovered as uniquely effective in the cross-coupling of different phenols with high chemo-and regioselectivity.
- Lee, Young Eun,Cao, Trung,Torruellas, Carilyn,Kozlowski, Marisa C.
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supporting information
p. 6782 - 6785
(2014/06/09)
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- {Cu2+-Co3+-Cu2+} and {Cu2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu+} (3), {Cu+-Fe3+-Cu+} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes.
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2015/04/27)
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- {Cu2+-Co3+-Cu2+} and {Cu 2+-Fe3+-Cu2+} heterobimetallic complexes and their catalytic properties
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We report on the heterobimetallic complexes {Cu+-Co 3+-Cu+} (3), {Cu+-Fe3+-Cu +} (4), {Cu2+-Co3+-Cu2+} (5), and {Cu2+-Fe3+-Cu2+} (6) and show their catalytic applications in the oxidation of hindered phenols and the oxidative coupling of terminal alkynes. The former reaction produces C-C-coupled and dealkylated products, whereas the latter leads to the homo- and heterocoupling of terminal alkynes. The facile redox interconversion between Cu+ and Cu 2+ for the secondary metal ions in these heterobimetallic complexes appears to be essential for the observed catalysis, and an important design aspect is better substrate accessibility and the use of molecular oxygen as the sole oxidant. Heterobimetallic complexes {Cu+-Co3+-Cu +} (3), {Cu+-Fe3+-Cu+} (4), {Cu 2+-Co3+-Cu2+} (5), and {Cu2+-Fe 3+-Cu2+} (6) have been used as catalysts for the oxidation of substituted phenols and the oxidative homo- and heterocoupling of terminal alkynes. Copyright
- Srivastava, Sumit,Ali, Afsar,Tyagi, Adish,Gupta, Rajeev
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p. 2113 - 2123
(2014/05/06)
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- Role of steric hindrance in the Newman-Kwart rearrangement and in the synthesis and photophysical properties of arylsulfanyl tetrapyrazinoporphyrazines
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Conditions for the Newman-Kwart rearrangement of phenols into thiophenols were investigated in relation to the bulkiness of substituents at the 2 and 6 positions of the starting phenol derivative with an emphasis on eliminating side reactions. Thiophenols with different 2,6-disubstitution patterns (including hydrogen, methyl, isopropyl or tert-butyl groups) were used for the synthesis of 5,6-bis(arylsulfanyl)pyrazine-2,3-dicarbonitriles that underwent cyclotetramerization leading to the corresponding zinc tetrapyrazinoporphyrazines (TPyzPz), aza-analogues of phthalocyanines. Several methods for the cyclotetramerization were attempted to eliminate problematic side reactions. Magnesium butoxide was found as the most suitable cyclotetramerization agent and afforded TPyzPzs in reasonable yields of approximately 30% under mild conditions. The varying arrangements of the peripheral substitutions resulting from the different bulkiness of the substituents were demonstrated by the X-ray structures of the pyrazine-2,3-dicarbonitriles. The prepared zinc arylsulfanyl TPyzPzs showed an absorption maximum at a Q-band over 650 nm, fluorescence quantum yields between 0.078 and 0.20, and singlet oxygen quantum yields ranging 0.58-0.69. TPyzPzs with isopropyl groups were found to be the best derivatives in this series as they combined facile cyclotetramerization, no aggregation, and good photophysical properties, which makes them potentially suitable for photodynamic therapy.
- Novakova, Veronika,Miletin, Miroslav,Filandrova, Tereza,Lenco, Juraj,Ruiszicka, Ales,Zimcik, Petr
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p. 2082 - 2093
(2014/04/03)
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- A high-valent heterobimetallic [CuIII(μ-O)2Ni III]2+ core with nucleophilic oxo groups
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Cores and effect: Unlike homobimetallic analogues, the heterobimetallic CuNi bis(μ-oxo) diamond core has nucleophilic oxo groups. A similar heterobimetallic core may, therefore, act as a viable intermediate during the deformylation of fatty aldehydes by cyanobacterial aldehyde decarbonylase. Copyright
- Kundu, Subrata,Pfaff, Florian Felix,Miceli, Enrico,Zaharieva, Ivelina,Herwig, Christian,Yao, Shenglai,Farquhar, Erik R.,Kuhlmann, Uwe,Bill, Eckhard,Hildebrandt, Peter,Dau, Holger,Driess, Matthias,Limberg, Christian,Ray, Kallol
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supporting information
p. 5622 - 5626
(2013/06/27)
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- An efficient reduction of quinones by formate-palladium/carbon system
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Ammonium formate in presence of palladium-carbon is an efficient system for catalytic transfer hydrogenation of several functional groups under mild conditions. However, this system was not found effective for reduction of quinones to hydroquinones, although reduction could be effected with phosphinic acid, phosphinates or cyclohexene as donors. A reexamination of this reaction suggested that formates were good hydrogen donors in this reduction but the reaction was inhibited due to quinhydrone formation. A simple expedient of maintaining low concentration of quinone during catalytic transfer hydrogenation reduction gave excellent yields of the hydroquinone. Compared to formates, formic acid was found to be a poor hydrogen donor.
- Pande, Poorn Prakash
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experimental part
p. 2549 - 2553
(2010/11/05)
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- Synthesis, characterization and catalytic activity of resin-based diiron(IH) interphase catalysts: Model for methane monooxygenase
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Three resin-based μ-oxo diiron(III) interface catalysts have been successfully prepared to model the functional properties of methane monooxygenase (MMO). The catalysts were characterized and exhibited the catalytic activities in the oxidation of alkanes to responding alcohols and ketones in acetonitrile at room temperature by 30% hydroperoxide (H 2O2) or tert-butyl hydroperoxide (TBHP) as the oxidants. For 2,6-di-tert-butylphenol as the substrate, the C-C coupling was found in the two reaction systems. The reaction mechanisms were proposed with the predominant radical mechanism.
- Shan,Qian,Zhang,Luo
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scheme or table
p. 163 - 168
(2009/09/06)
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- Electron transfer between protonated and unprotonated phenoxyl radicals
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(Chemical Equation Presented) The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO2 to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H2O containing an added acid provides eventually p-benzoquinone 39 and 4,4′-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.
- Omura, Kanji
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p. 858 - 867
(2008/09/19)
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- ABCA1 STABILIZER
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To provide a pharmaceutically effective prophylactic/preventive agent for low-HDL cholesterolemia, focusing on an HDL-generating mechanism. The ABCA1 stabilizer of the present invention contains a bisphenol-type compound selected form probucol spiroquinone, probucol diphenoquinone, and probucol bisphenol as an effective ingredient. The ABCA1 stabilizer can continuously and stably express ABCA1 by a mechanism quite different from that of conventional processes, and thus is useful as prophylactic/preventive agent for low-HDL cholesterolemia or arteriosclerosis.
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Page/Page column 9
(2008/06/13)
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- PREPARATION OF BIPHENOLS BY OXIDATIVE COUPLING OF ALKYLPHENOLS USING A RECYCLABLE COPPER CATALYST
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A method for producing biphenols by oxidative coupling of dialkylphenols which proceeds in two stages is disclosed, using a copper-amine complex which is catalytically active in each stage. A novel copper-amine complex is also disclosed which exhibits high catalytic activity for the oxidative coupling of substituted phenols under mild conditions, has dual (two stage) activity, and can be readily recycled and reused.
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- The reaction of peroxynitrite with organic molecules bearing a biologically important functionality. The multiplicity of reaction modes as exemplified by hydroxylation, nitration, nitrosation, dealkylation, oxygenation, and oxidative dimerization and cleavage
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The reactions of peroxynitrite with a variety of organic molecules which include a biologically important functionality have been examined to construct a simple model for the peroxynitrite-induced in vivo transformations as well as a chemical probe for the active species involved therein. Phenols were found to undergo hydroxylation, nitration, oxidative dimerization, and oxidation to cyclohexadienones and quinones. The ring nitration of catechol was confirmed for the first time in the in vitro reaction of peroxynitrite. Dealkylation and N-oxide formation were the major reaction modes observed for N,N-dimethyl-p-toluidine. 1,2-Phenylenediamine gave benzotriazole in high yield. The electron-deficient C-C double bond in 1,4-naphthoquinone underwent epoxidation, while the electron-rich C-C double bond in α-methylstyrene suffered oxidative cleavage to acetophenone. The activated double bond in trans-stilbene underwent oxidative cleavage and epoxidation in parallel to give benzaldehyde and trans-stilbene oxide as the major products. The triple bond in diphenylacetylene was simply oxygenated to form benzil, together with trace amounts of ring nitration products. 1-Phenylethanol, imidazole, 2′-deoxyadenosine, and 2′-deoxyguanosine were all quite slow to react, while uracil and cytosine were almost inert to peroxynitrite. The reaction modes exhibited by peroxynitrite are too widespread and complicated to explain the whole mechanistic pathway in terms of a single active species. All reaction modes observed for the peroxynitrite to date could be classified into five categories according to their types: i) electron transfer type, ii) O-electrophilic type, iii) N-electrophilic type, iv) O-nucleophilic type, and v) radical type. Some of these may compete under certain conditions. The active species involved in each of these types of reactions are as follows: i) NO+, NO2, and OH, ii) ONOOH, iii) ONOOH and NO+, iv) OOH- and ONOO-, and v) NO2 and OH.
- Nonoyama, Nobuaki,Oshima, Hiroshi,Shoda, Chizuru,Suzuki, Hitomi
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p. 2385 - 2395
(2007/10/03)
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- Reaction of Sulfur with 2,6-Di-tert-butylphenol in Dipolar Aprotic Solvenys
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In dipolar aprotic solvents 2,6-di-tert-butylphenol reversibly reacts with elemental sulfur to form a mixture of bis(3,5-di-tert-butyl-4-hydroxyphenyl) polysulfides. The reverse process is initiated by hydrogen sulfide, and removal of the latter from the reaction mixture makes possible the polysulfides to be obtained in nearly quantitative yield.
- Bukharov, S. V.,Konoshenko, L. V.,Solov'eva, S E.,Gainullin, V. I.,Syakaev, V. V.,Mannanov, T. G.,Chugunov, Yu. V.,Samuilov, Ya. D.
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p. 126 - 129
(2007/10/03)
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- Isolation of cross-coupling products in model studies on the photochemical modification of proteins by tiaprofenic acid
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To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C-C- and C-O-connected p-cresol 'dimers', together with DTPA hydrodimers. The p-cresol-DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of 'dimers' can be related to protein photo-crosslinking, through the coupling of two tyrosine units. On the other hand, phenol-(D)TPA cross-coupling may be relevant to the understanding of drug-protein photobinding.
- Miranda, Miguel Angel,Perez-Prieto, Julia,Lahoz, Agustin,Morera, Isabel M.,Sarabia, Zaideth,Martinez-Manez, Ramon,Castell, Jose V.
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p. 497 - 502
(2007/10/03)
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- Rapid conversion of phenols to p-benzoquinones under acidic conditions with lead dioxide
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Treatment of 4-unsubstituted and 4-halogenated phenols with PbO2 and 70% HClO4 in AcOH afforded the corresponding p-benzoquinones in fair to high yields. The oxidation of 4-substituted 2,6-di-tertbutylphenols 6 with PbO2 and 70% HClO4 in acetone gave 2,6-di-tert-butyl-p-benzoquinone (2).
- Omura, Kanji
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p. 1145 - 1148
(2007/10/03)
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- Reactivity of 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol, and (3,5-di-tert-butyl-4-hydroxybenzyl)methyl ether at oxidation by oxygen in basic solutions
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Reactivity at oxidation in basic water-ethanol solutions of the fallowing phenols: 3,5-di-tert-butyl-4-hydroxybenzaldehyde, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol, and (3,5-di-tert-butyl-4-hydroxybenzyl)methyl ether was studied as affected by α-located oxygen-containing functional groups and the base nature. It is shown that the substrate reactivity drops in the order: alcohol ≥ ether > aldehyde. In the presence of NaOH, Na2CO3, and NaHCO3 the alcohol and the ether are similar in efficiency, while in aqueous ammonia the alcohol reactivity is much higher than that of ether. Aldehyde oxidizes in ammoniak with the tenfold faster than in solutions of NaOH, Na2CO3, and NaHCO3.
- Fedulina,Klindukhov
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p. 692 - 698
(2007/10/03)
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- Stabilizer of isoprene rubber and thermoplastic compositions on its base
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The stabilizing efficiency was studied of the products of oxidative dehydration of 4-methyl-2,6-di-tert-butylphenol with 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone in SKI-3 synthetic isoprene rubber and a thermoplastic composition based on SKI-3 and polypropylene.
- Fazlieva,Mukmeneva,Bukharov,Vol'fson
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p. 1252 - 1253
(2007/10/03)
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- A mechanistic approach to the reaction of 2,6-di-tert-butylphenol with an iodinating agent in methanol: Electrophilically assisted solvolysis of intermediary 4-iodocyclohexa-2,5-dienones
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Reactions of the title phenol (1) and of 4-iodophenol 2 with an iodinating agent, I2 and H2O2, are conducted in MeOH for varying times with varying amounts of I2, and the results are compared. The reaction of 1 gives 2, 4,4′-biphenol 3, 4,4′- diphenoquinone 4, 4-methoxyphenol 5, and p-benzoquinone 6, exclusively. The yields of the phenolic products (2, 3, and 5) vary with reaction time, but they disappear or almost disappear eventually, to make 4 and 6 the almost exclusive products. The reaction of 2 always gives 4 and 6 alone. In both of the reactions of 1 and of 2, employment of a higher initial I2 concentration not only completes the formation of 4 and 6 faster but also makes the final proportion of 6 higher. However, the ultimate yield of 6 from the reaction of 1 is significantly higher than that from the reaction of 2, irrespective of the initial I2 concentration. These results are interpreted as follows. 4-Iodocyclohexa-2,5-dienone 12, the primary product of electrophilic iodination of 1, undergoes solvolysis (methanolysis), which is electrophilically assisted by I2. The solvolysis of 12 can be so fast as to overwhelm its prototropic rearrangement to give 2. 4-Methoxycyclohexa-2,5-dienone 13, which is the primary product of the methanolysis of 12 and is suggested to be detectable by 1H NMR spectroscopy, is converted into 6 via 5. Benzoquinone 6 can also arise from 4,4-diiodocyclohexa-2,5-dienone 7, the product of iodination of 2, by an analogous mechanism. The selectivity of the formation of 6 from 7 is low because the competing reaction, homolytic scission of the C-I bond in 7, predominates. The mechanism of the formation of 3 and 4 is also discussed.
- Omura, Kanji
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p. 2006 - 2012
(2007/10/03)
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- Base-catalyzed dehalogenation of 2,6-di-tert-butyl-4-iodophenol formation and structure of a new oxocyclohexadienylidene bisphenol
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2,6-Di-tert-butyl-4-iodophenol (1) does not react to the keto carbene 4 under strongly basic conditions and exclusion of oxygen, in contrast to a report in the literature. In the presence of oxygen, however, oxidation takes place. Reaction times and product pattern strongly depend on the concentration of O2. Besides biphenyl 2, diphenoquinone 3, and quinone 5, a new (oxocyclohexadienylidene)bisphenol 6 was isolated, and its molecular structure was determined by X-ray crystallography. A radical mechanism is suggested for the formation of the above products from 1. The bisphenol 6 was also synthesized by thermolysis of the quinone diazide 11 in the presence of 3. VCH Verlagsgesellschaft mbH, 1996.
- Reischl, Gerald,Maichle-Moessmer, Caecilia,Abram, Sonja,Rieker, Anton
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p. 1183 - 1186
(2007/10/03)
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- SYNTHESIS OF 2,6-DI-tert-BUTYL-4-(3,5-DI-tert-BUTYL-4-HYDROXYBENZYLIDENE)-2,5-CYCLOHEXADIENONE
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2,6-Di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2,5-cyclohexadienone has been prepared in 63-92percent yield by oxidative dehydrogenation of 4,4'-methylenebis(2,6-di-tert-butylphenol) with various quinones.The products of quinone reduction have been isolated.
- Mukmeneva, N. A.,Bukharov, S. V.,Kadyrova, V. Kh.,Zharkova, V. M.
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p. 1350 - 1351
(2007/10/02)
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- A New Synthetic Approach to Pyridinium N-Phenoxide Betaine Dyes
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The reaction of 3,5-di-tert-butyl-4-oxo-2,5-cyclohexadienylidene (3d) with pyridine affords 2,6-di-tert-butyl-4-(2,4,6-tri-tert-butylpyridinio)phenolate (1d) - which is not accessible by the classical route via pyrylium salts - in reasonable yield.Carbene 3d is generated by thermal decomposition of the corresponding quinone diazide 2d in cyclohexane.Betaine 1d shows the expected large solvatochromism. - Key Words: Betaine dye / Solvatochromism / Ylide / Carbene reaction
- Sander, Wolfram,Hintze, Frank
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p. 267 - 270
(2007/10/02)
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- Reinvestigation on the Reaction of 2,6-Di-tert-butylbenzoquinone Methide and 2,6-Di-tert-butylphenol
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The reaction of quinone methide 1 and phenol 2 in equimolar amounts was investigated in pentane at 30 deg C.Products were isolated by means of column chromatography on SiO2.There was a marked difference in product distribution between the reactions in the presence and absence of added Et3N.Dienones 3 and 10 were obtained only from the former reaction, while formation of 1,2-bis(4-hydroxyphenyl)ethane 18 and 4,4'-dihydroxybiphenyl 20 was overwhelming in the latter reaction.Other products from both reactions were relatively small quantities of 4,4'-stilbenequinone 17, 4,4'-diphenoquinone 21, and bis(4-hydroxyphenyl)methane 24, but dienone 4 was not obtained.Compounds 20 and 24 obtained from the latter reaction were formed by isomerization of dienones 19 and 23, respectively, during chromatography.The reaction is initiated by dimerization of 1 to generate biradical 11.Subsequent processes involving hydrogenation-dehydrogenation, coupling-dissociation, and dienone-phenol rearrangement account for the formation or the lack of formation of the products.The difference in product distribution is ascribed to capability of Et3N to catalyze the isomerization.Quinone methide 1 also adds to 2 to give 23.The decay of 1 in the presence of both 2 and phenol 6 gave dienone 8 additionally.The formation of 24 and 4 was facilitated by conducting the reaction of 1 and 2 in DMSO.Dehydrogenation of 10 and 3 with PbO2 afforded spirodienones 27 and 28, respectively.Compounds 27 and 28 were unstable, and their decay in solution was investigated in the presence or absence of added 2.The results show that the decay is initiated by homolytic scission of the C-C bond connecting the dienone rings in the cyclopentane (in 27) and cyclohexane (in 28) rings.Compound 28 is novel in that it bears two kinds of such C-C bonds.Reversibility of the dimerization of 1 is suggested.
- Omura, Kanji
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p. 306 - 312
(2007/10/02)
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