- Bifunctional Cs?Au/Co3O4 (Basic and Redox)-Catalyzed Oxidative Synthesis of Aromatic Azo Compounds from Anilines
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An eco-friendly alkali-promoted (Cs?Au/Co3O4) catalyst, with redox and basic properties for the oxidative dehydrogenative coupling of anilines to symmetrical and unsymmetrical aromatic azo compounds, was developed. We realized a base additive- and molecular O2 oxidant-free process (using air), with reasonable reusability of the catalyst achieved under milder reaction conditions. Notably, the enhanced catalytic activity was also linked to the increased basic site concentration, low reduction temperatures, and the effect of lattice oxygen on the nanomaterials. The increased basic strength of the cation-promoted catalyst improved the electron density of the active Au species, resulting in higher yields of the desired aromatic azo compounds.
- Akinnawo, Christianah Aarinola,Alimi, Oyekunle Azeez,Fapojuwo, Dele Peter,Meijboom, Reinout,Mogudi, Batsile M.,Onisuru, Oluwatayo Racheal,Oseghale, Charles O.
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supporting information
p. 5063 - 5073
(2021/09/30)
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- Invisible Silver Guests Boost Order in a Framework That Cyclizes and Deposits Ag3Sb Nanodots
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The infusion of metal guests into (i.e., metalating) the porous medium of metal-organic frameworks (MOFs) is a topical approach to wide-ranging functionalization purposes. We report the notable interactions of AgSbF6 guests with the designer MOF host ZrL1 [Zr6O4(OH)7(L1)4.5(H2O)4]. (1) The heavy-atom guests of AgSbF6 induce order in the MOF host to allow the movable alkyne side arm to be fully located by X-ray diffraction, but they themselves curiously remain highly disordered and absent in the strucutral model. The enhanced order of the framework can be generally ascribed to interaction of the silver guests with the host alkyne and thioether functions, while the invisible heavy-atom guest represents a new phenomenon in the metalation of open framework materials. (2) The AgSbF6 guests also participate in the thermocyclization of the vicinal alkyne units of the L1 linker (at 450 °C) and form the rare nanoparticle of Ag3Sb supported on the concomitantly formed nanographene network. The resulted composite exhibits high electrical conductivity (1.0 S/cm) as well as useful, mitigated catalytic activity for selectively converting nitroarenes into the industrially important azo compounds, i.e., without overshooting to form the amine side products. The heterogeneous/cyclable catalysis entails only the cheap reducing reagents of NaBH4, ethanol, and water, with yields being generally close to 90%.
- Ahn, Dohyun,Cheng, Shengxian,Feng, Weijin,He, Jun,Hu, Jieying,Xin, Yinger,Xu, Zhengtao,Zeller, Matthias
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p. 5757 - 5763
(2021/05/04)
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- Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline
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Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system (‘dip-catalyst’) and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20–30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H2 pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.
- Adeyeye Nafiu, Sodiq,Aziz, Abdul,Shaheen Shah, Syed,Shaikh, M. Nasiruzzaman
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p. 1956 - 1966
(2021/06/18)
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- Continuous and green microflow synthesis of azobenzene compounds catalyzed by consecutively prepared tetrahedron CuBr
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An environmentally friendly and cross-selective process intensification for the continuous synthesis of symmetric aromatic azo compounds by using self-made cuprous bromide as the catalyst under mild conditions in the microreactor was developed. A novel tetrahedron cuprous bromide catalyst which shows outstanding catalytic activity and satisfactory stability has been synthesized in continuous flow microreactor. The online immobilization of self-made cuprous bromide on the catalyst bed achieved oxidative coupling of aromatic amines (oxygen as oxidant) and high-performance gas–liquid–solid three-phase reaction, which strongly limited the possibility of undesired reaction pathways, improving product selectivity and reducing waste generation. Meanwhile, the yield of azo-coupling reaction was up to 98% under optimized condition. As compared with earlier traditional method (diazotization reaction) for synthesizing azobenzene, the designed micro-flow process displays signi?cant advances in terms of selectivity, waste emissions, sustainability and productivity. The combination of online immobilization of self-made cuprous bromide and precise and safe control through the microreactor provides a green solution for the industrial production of valuable aromatic azo compounds.
- Qin, Hong,Liu, Chengkou,Lv, Niuniu,He, Wei,Meng, Jingjing,Fang, Zheng,Guo, Kai
-
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- Selective Propargylation of Diaryl Azo Compounds Using Metallic Barium
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The Barbier-type propargylation of azo compounds with α,γ-disubstituted propargylic tosylates was achieved by using metallic barium as the promoter. Various propargylated hydrazines (α-adducts) were exclusively synthesized from the corresponding propargylic tosylates and azobenzenes (diaryldiazenes). The thus-obtained propargylic hydrazines were further efficiently converted into propargylic amines by reductive N-N bond cleavage. Benzidine rearrangement of the propargylic hydrazines was also attempted.
- Yanagisawa, Akira,Heima, Toshihiko,Watanabe, Kana,Haeno, Shun
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supporting information
p. 1817 - 1822
(2020/09/02)
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- Tandem selective reduction of nitroarenes catalyzed by palladium nanoclusters
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We report a catalytic tandem reduction of nitroarenes by sodium borohydride (NaBH4) in aqueous solution under ambient conditions, which can selectively produce five categories of nitrogen-containing compounds: anilines, N-aryl hydroxylamines, azoxy-, azo- and hydrazo-compounds. The catalyst is in situ-generated ultrasmall palladium nanoclusters (Pd NCs, diameter of 1.3 ± 0.3 nm) from the reduction of Pd(OAc)2 by NaBH4. These highly active Pd NCs are stabilized by surface-coordinated nitroarenes, which inhibit the further growth and aggregation of Pd NCs. By controlling the concentration of Pd(OAc)2 (0.1-0.5 mol% of nitroarene) and NaBH4, the water/ethanol solvent ratio and the tandem reaction sequence, each of the five categories of N-containing compounds can be obtained with excellent yields (up to 98%) in less than 30 min at room temperature. This tunable catalytic tandem reaction works efficiently with a broad range of nitroarene substrates and offers a green and sustainable method for the rapid and large-scale production of valuable N-containing chemicals.
- Yan, Ziqiang,Xie, Xiaoyu,Song, Qun,Ma, Fulei,Sui, Xinyu,Huo, Ziyu,Ma, Mingming
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supporting information
p. 1301 - 1307
(2020/03/11)
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- Synthesis of 2 - fluoro aniline compounds of the method
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The invention discloses a method for synthesizing 2 - fluoro aniline compounds of the method, the method is: shown in formula Ia aniline compound of formula Ib α and β shown aniline compound as raw materials, through coupling reaction shown [...] azobenzene compound II, then the type II shown azobenzene compound with a palladium catalyst, fluorination reagent, additive, organic solvent, in the 30 - 150 °C temperature closed agitating the fluorination reaction, [...] compound of formula III, type III compounds are shown in the reaction under the action of a reducing [...] shown IV 2 - fluoro aniline compounds; this invention synthetic 2 - fluoro aniline compounds substrate wide adaptability, mild reaction conditions, the operation is simple, fluorinated and good selectivity, [...] aniline compounds is prepared by many drug molecule is an important intermediate and starting material, wide application prospects.
- -
-
Paragraph 0092; 0094
(2019/05/15)
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- Method for catalytically synthesizing azobenzene compound through double-metal composite oxide
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The invention discloses a method for catalytically synthesizing an azobenzene compound through a double-metal composite oxide and belongs to the technical field of catalytic synthesis of azobenzene. According to the method disclosed by the invention, under the action of the double-metal composite oxide, air or oxygen is used as an oxidant, so that amines containing different substituent groups aredirectly oxidized and coupled under a moderate condition to synthesize the azobenzene compound. A catalysis system adopted by the method has moderate reaction conditions and high selectivity; the synthesis of the azobenzene compound can be efficiently catalyzed by carrying out reacting at 60 DEG C and in the air; transition metal which is cheap and easy to obtain and contains iron, cobalt, nickel, aluminum, manganese and copper is used as the double-metal composite oxide, so that the availability of a double-metal composite oxide catalyst is improved.
- -
-
Paragraph 0061; 0062
(2019/03/08)
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- Conversion of anilines into azobenzenes in acetic acid with perborate and Mo(VI): correlation of reactivities
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Azobenzenes are extensively used to dye textiles and leather and by tuning the substituent in the ring, vivid colours are obtained. Here, we report preparation of a large number of azobenzenes in good yield from commercially available anilines using sodium perborate (SPB) and catalytic amount of Na2MoO4 under mild conditions. Glacial acetic acid is the solvent of choice and the aniline to azobenzene conversion is zero, first and first orders with respect to SPB, Na2MoO4 and aniline, respectively. Based on the kinetic orders, UV–visible spectra and cyclic voltammograms, the conversion mechanism has been suggested. The reaction rates of about 50 anilines at 20–50?°C and their energy and entropy of activation conform to the isokinetic or Exner relationship and compensation effect, respectively. However, the reaction rates, deduced by the so far adopted method, fail to comply with the Hammett correlation. The specific reaction rates of molecular anilines, obtained through a modified calculation, conform to the Hammett relationship. Thus, this work presents a convenient inexpensive non-hazardous method of preparation of a larger number of azobenzenes, and shows the requirement of modification in obtaining the true reaction rates of anilines in acetic acid and the validity of Hammett relationship in the conversion process, indicating operation of a common mechanism.
- Karunakaran,Venkataramanan
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p. 375 - 385
(2019/02/14)
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- Aerobic Oxidative coupling of aniline catalyzed by one-dimensional manganese hydroxide nanomaterials
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The aerobic oxidative coupling of aniline is an effective process for producing aromatic azo compounds, which are widely used in the organic chemical industry. The development of heterogeneous catalysts for this reaction would be advantageous because of their recyclability and convenience in posttreatment. In this work, one-dimensional Mn(OH) 2 nanostructure with various shapes were synthesized through the adjustment of various surfactants. The as-synthesized Mn(OH) 2 nanobelts and nanowires showed superior catalytic activity in the activation of oxygen and aniline. Aromatic azo compounds with a variety of substituents were produced through the coupling of the corresponding anilines without additives under ambient conditions.
- Miao, Hui,Ma, Kelong,Hu, Shiwei,Li, Ruiqian,Sun, Lin,Cui, Yumin
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supporting information
p. 552 - 556
(2019/03/08)
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- Visible-light-promoted oxidative dehydrogenation of hydrazobenzenes and transfer hydrogenation of azobenzenes
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Azo compounds are widely used in the pharmaceutical and chemical industries. Here, we report the use of a non-metal photo-redox catalyst, Eosin Y, to synthesize azo compounds from hydrazine derivatives. The use of visible-light with air as the oxidant makes this process sustainable and practical. Moreover, the visible-light-driven, photo-redox-catalyzed transfer hydrogenation of azobenzenes is compatible with a series of hydrogen donors such as phenyl hydrazine and cyclic amines. Compared with traditional (thermal/transition-metal) methods, our process avoids the issue of over-reduction to aniline, which extends the applicability of photo-redox catalysis and confirms it as a useful tool for synthetic organic chemistry.
- Wang, Xianya,Wang, Xianjin,Xia, Chungu,Wu, Lipeng
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supporting information
p. 4189 - 4193
(2019/08/07)
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- Au@zirconium-phosphonate nanoparticles as an effective catalytic system for the chemoselective and switchable reduction of nitroarenes
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In the present paper, a novel inorganic-organic layered material, a zirconium phosphate aminoethyl phosphonate, ZP(AEP), bearing aminoethyl groups on the layer surface, was used to immobilize AuNPs by a two-step procedure. The gold-based catalyst, Au1@ZP(AEP), containing 1 wt% Au, was characterized in terms of physico-chemical properties and TEM analysis revealed that the AuNPs have a spherical shape and an average size of 7.8 (±2.4) nm. Au1@ZP(AEP) proved its high efficiency for the chemoselective reduction of nitroarenes under mild conditions. Both batch and flow condition protocols have been defined. The catalytic system has been proven to be able to easily switch chemoselectivity allowing the control of the reduction of a series of nitroaromatics towards their corresponding azoxyarenes (2a-k) or anilines (2a-l) in 96% EtOH or abs EtOH, respectively, by using NaBH4 as a reducing agent, in good to excellent yields. Recovery and reuse of the catalytic system has been investigated proving the benefits of the flow approach.
- Ferlin, Francesco,Cappelletti, Matteo,Vivani, Riccardo,Pica, Monica,Piermatti, Oriana,Vaccaro, Luigi
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supporting information
p. 614 - 626
(2019/02/13)
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- Immobilized antimony species on magnetite: A novel and highly efficient magnetically reusable nanocatalyst for direct and gram-scale reductive-coupling of nitroarenes to azoarenes
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In this study, magnetic nanoparticles of Fe3O4@SbFx from the immobilization of SbF3 on magnetite were synthesized. The prepared nanocomposite system was then characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry and inductively coupled plasma optical emission spectroscopy. Next, the catalytic activity of Fe3O4@SbFx MNPs was highlighted by one-pot reductive-coupling of aromatic nitro compounds to the corresponding azoarene materials with NaBH4. The reactions were carried out in refluxing EtOH within 6-25 min to afford the products in high yields. The reusability of the Sb-magnetite system was also studied for 6 consecutive cycles without significant loss of catalytic activity. This synthetic protocol provided several advantages in terms of introducing a novel catalytic system based on antimony species for direct and gram-scale preparation of azoarenes from nitroarenes, low loading of the nanocatalyst, mild reaction conditions, using ethanol as a green and economic solvent and high yield of the products.
- Zeynizadeh, Behzad,Faraji, Fariba
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p. 13112 - 13121
(2019/05/10)
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- Visible-light triggered selective reduction of nitroarenes to azo compounds catalysed by Ag@organic molecular cages
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Herein, a new Ag nanoparticle (Ag NP) loaded organic molecular cage is reported. The obtained Ag@1 can act as a highly efficient heterogeneous catalyst for the selective reduction of nitroarenes to azo compounds under visible-light irradiation.
- Chen, Gong-Jun,Xin, Wen-Ling,Wang, Jing-Si,Cheng, Jun-Yan,Dong, Yu-Bin
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supporting information
p. 3586 - 3589
(2019/03/26)
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- Rh(III)-catalyzed [4?+?1]-annulation of azobenzenes with α- carbonyl sulfoxonium ylides toward 3-acyl-(2H)-indazoles
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A Rh(III)-catalyzed [4 + 1]-annulation of azobenzenes with α- carbonyl sulfoxonium ylides was developed to access 2H-indazoles in moderate to excellent yields with good functional group compatibilities. It proceeded with the sequential insertion of the Rh(III) carbene to the C?H bond and cyclization steps, where sulfoxonium ylides served as efficient and stable carbene precursor.
- Zhu, Jiawei,Sun, Song,Cheng, Jiang
-
supporting information
p. 2284 - 2287
(2018/05/23)
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- Super electron donor-mediated reductive transformation of nitrobenzenes: A novel strategy to synthesize azobenzenes and phenazines
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The transformation of nitrobenzenes into azobenzenes by pyridine-derived super electron donor 2 is described. This method provides an efficient synthesis of azobenzenes because of not requiring the use of expensive transition-metals, toxic or flammable reagents, or harsh conditions. Moreover, when using 2-fluoronitrobenzenes as substrates, phenazines were found to be obtained. The process affords a novel synthesis of phenazines.
- Nozawa-Kumada, Kanako,Abe, Erina,Ito, Shungo,Shigeno, Masanori,Kondo, Yoshinori
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supporting information
p. 3095 - 3098
(2018/05/22)
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- Method for preparing azobenzene compound with continuous flow
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The invention discloses a method for preparing an azobenzene compound with continuous flows. The method comprises the following steps: (1) carrying out on-line filling of a columnar microreactor withcuprous bromide prepared with continuous flows; (2) carrying out on-line water washing and ethanol washing on the columnar microreactor filled with the cuprous bromide; (3) dissolving aromatic amine and pyridine into a solvent so as to obtain a mixed solution; (4) respectively inputting and mixing the mixed solution and oxygen into a casing type flow reactor simultaneously so as to obtain a gas-liquid mixture; (5) pumping the gas-liquid mixture into the columnar microreactor of the step (2) to carry out an oxidative coupling reaction, thereby obtaining an azobenzene compound. By adopting the method, integration of preparation, on-line filling and washing of a cuprous bromide catalyst and synthesis of an azo product in a synthesis process of the azobenzene compound is achieved, oxidation ofthe cuprous bromide in preparation and manual filling processes and a process of joining in catalytic synthesis of the azobenzene compound is reduced, and the mixing efficiency of three phases of gases, liquids and solids is improved.
- -
-
Paragraph 0047; 0048; 0085; 0086; 0088
(2018/11/03)
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- Kinetics and thermodynamics of oxidation of some meta-substituted anilines by tetrabutylammonium bromochromate in aqueous acetic acid medium
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The tetrabutylammonium bromochromate (TBABC) oxidation of anilines, in an aqueous acetic acid medium in the presence of perchloric acid is described. The reaction is first order with respect to aniline, TBABC and acid. The reaction rate has been determined at different temperatures and activation parameters calculated. The TBABC oxidation of meta-substituted anilines obeys Hammett relationships.
- Jabir, Shaik,Asghar, Basim H.,Mansoor, S. Sheik
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p. 288 - 295
(2017/03/17)
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- Substrate-Controlled Transformation of Azobenzenes to Indazoles and Indoles via Rh(III)-Catalysis
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Rh(III)-catalyzed substrate-controlled transformation of azobenzenes to indazoles and 2-acyl (NH) indoles is achieved via C-H functionalization. Generally, good functional groups tolerance, satisfying yields, and excellent regio-selectivity are achieved in this reaction. Mechanistically, the reaction with acrylates undergoes β-hydride elimination, while the reaction with vinyl ketones or acrylamides undergoes nucleophilic addition. Copper acetate was supposed to play different roles in the β-hydride elimination to furnish indazoles and nucleophilic addition of C-Rh bond to deliver 2-acyl (NH) indoles.
- Cai, Shangjun,Lin, Songyun,Yi, Xiangli,Xi, Chanjuan
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p. 512 - 520
(2017/04/26)
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- Palladium-Catalyzed Carbonylative Cyclization of Azoarenes
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In this communication, we established an interesting palladium-catalyzed carbonylation protocol for the intramolecular cyclization of azoarenes. With Mo(CO)6 as the solid CO source and through C(sp2)?H bond activation, a series of azoarenes were transformed into the corresponding 2-arylindazolones in moderate to good yields. Notably, not only symmetrical azoarenes, but also unsymmetrical substrates underwent the reaction with excellent regioselectivity.
- Wang, Zechao,Yin, Zhiping,Zhu, Fengxiang,Li, Yahui,Wu, Xiao-Feng
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p. 3637 - 3640
(2017/10/13)
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- Aromatic amine oxidation process for preparing aromatic azobenzene method
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The invention relates to a method for preparing an aromatic azo compound by utilizing aromatic amine oxidation. In the method, air or oxygen serves as an oxygen source, and under the effect of a catalyst, aromatic amine is oxidized into the aromatic azo compound. The method is high in oxidization efficiency and product yield; the air or the oxygen serves as the oxygen source, and the method is economical and environmentally friendly. The product and the catalyst can be separated easily, and the aftertreatment is simple. The catalyst is easy to reuse, and the method has very good application prospect.
- -
-
Paragraph 0013; 0017
(2017/10/11)
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- Oxidative coupling of anilines to azobenzenes using heterogeneous manganese oxide catalysts
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We herein report the transition metal oxide-catalyzed synthesis of azobenzenes through the oxidative coupling of anilines. An octahedral molecular sieve of manganese oxide, OMS-2, exhibited the best activity and selectivity. Nine examples of symmetric azobenzenes and twenty unsymmetric ones were synthesized with 62-99% conversion and 64-99% selectivity. In the aniline cross-coupling reactions, the difference of the Hammett constants of two substituted groups (Δσ) determines the selectivity to unsymmetric azobenzenes, which are the major products at Δσ 0.32. In-depth studies reveal that the surface defect sites of the mixed-valence manganese oxide play a key role in facilitating electron transfer and activating molecular oxygen. The single-electron transfer (SET) reaction mechanism is proposed based on electron paramagnetic resonance and X-ray powder diffraction characterization.
- Wang, Min,Ma, Jiping,Yu, Miao,Zhang, Zhe,Wang, Feng
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p. 1940 - 1945
(2016/04/05)
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- Method for synthesizing aromatic azo compounds
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The invention disclose a method for synthesizing aromatic azo compounds and especially relates to a method for synthesizing aromatic azo compounds by catalyzing oxidation of aromatic aniline compounds to carry out coupled dehydrogenations by themselves by adopting a manganese oxide compound synthesized by potassium permanganate and manganese nitrate in an alkaline solution as the catalyst. The method can be used to conveniently synthesize symmetrical and dissymmetrical azo compounds; reaction conditions of the method are mild, the air is utilized as an oxygen source, and no additive is added therein; thus, the method has the characteristic of simple operation, strong universality of the catalyst system as well as high yield and selectivity.
- -
-
Paragraph 0028; 0029
(2016/11/17)
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- The palladium and copper contrast: A twist to products of different chemotypes and altered mechanistic pathways
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A novel contrast in palladium and copper catalysis is revealed to form products of different chemotypes resulting in a phenazine to azoarene twist through an altered mechanistic pathway (from non-radical C-H activation mode of C-N coupling to radical N-N coupling) during the oxidative self-coupling of anilines catalysed by Pd-Ag and Cu-Ag nanoclusters.
- Seth, Kapileswar,Roy, Sudipta Raha,Kumar, Asim,Chakraborti, Asit K.
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p. 2892 - 2896
(2016/05/24)
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- Formal [4+2] cycloaddition of 3-ethoxycyclobutanones with azo compounds
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Azobenzenes reacted with 3-ethoxycyclobutanoes to give 2,3-dihydro-pyridazin-4(1H)-ones by using EtAlCl2as a Lewis acid. Thus, ring cleavage of 3-ethoxycyclobutanones took place to form a zwitterionic intermediate by activation with EtAlCl2, and intermolecular formal [4+2] cycloaddition of the zwitterionic intermediate proceeded with azobenzenes to give 2,3-dihydro-pyridazin-4(1H)-ones after elimination of ethanol. Regioselectivity for cycloaddition of unsymmetrical azobenzenes, ring contraction and chemoselective reduction of 2,3-dihydro-pyridazin-4(1H)-ones, and [4+2] cycloaddition to 4-phenyl-1,2,4-triazolin-3,5-dione are also described.
- Shima, Yusuke,Matsuo, Jun-ichi
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supporting information
p. 4066 - 4069
(2016/08/18)
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- Single-atom dispersed Co-N-C catalyst: Structure identification and performance for hydrogenative coupling of nitroarenes
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Co-N-C catalysts are promising candidates for substituting platinum in electrocatalysis and organic transformations. The heterogeneity of the Co species resulting from high-temperature pyrolysis, however, encumbers the structural identification of active sites. Herein, we report a self-supporting Co-N-C catalyst wherein cobalt is dispersed exclusively as single atoms. By using sub-?ngstr?m-resolution HAADF-STEM in combination with XAFS and DFT calculation, the exact structure of the Co-N-C is identified to be CoN4C8-1-2O2, where the Co center atom is coordinated with four pyridinic N atoms in the graphitic layer, while two oxygen molecules are weakly adsorbed on Co atoms in perpendicular to the Co-N4 plane. This single-atom dispersed Co-N-C catalyst presents excellent performance for the chemoselective hydrogenation of nitroarenes to produce azo compounds under mild reaction conditions.
- Liu, Wengang,Zhang, Leilei,Yan, Wensheng,Liu, Xiaoyan,Yang, Xiaofeng,Miao, Shu,Wang, Wentao,Wang, Aiqin,Zhang, Tao
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p. 5758 - 5764
(2016/08/31)
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- Oxidation of aromatic anils in aniline moiety by meta-chloroperbenzoic acid in aqueous acitic medium
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The kinetics of oxidation of aromatic anils in aniline moiety by meta-chloroperbenzoic acid (m-CPBA) has been studied in aqueous acitic medium. The order of reaction was found to be second order with respect to aromatic anil and first order with respect to m-chloroperbenzoic acid. The increase of [H+] in this oxidation retards the rate of reaction. The effects of substituents on the oxidation rate were studied with 3 meta- and 5 para-substituted anils at five different temperatures. Thermodynamic parameters for the oxidation have been determined and discussed. meta-Chloroperbenzoic acid oxidation with substituted anils fulfills the isokinetic relationship and Exner relationship but not to any of the linear free energy relationships. The deviation of Hammett plot was noted and a concave downward curve was obtained for the anils with substituents in aniline moiety.
- Venkatesh,Karunakaran
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p. 2851 - 2855
(2015/12/12)
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- Copper-Promoted Tandem Reaction of Azobenzenes with Allyl Bromides via N=N Bond Cleavage for the Regioselective Synthesis of Quinolines
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A copper-promoted tandem reaction of a variety of azobenzenes and allyl bromides via N=N bond cleavage to regioselectively construct quinoline derivatives has been developed. The azobenzenes act as not only construction units but also an oxidant for quinoline formation.
- Yi, Xiangli,Xi, Chanjuan
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supporting information
p. 5836 - 5839
(2015/12/11)
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- Deoxygenative coupling of nitroarenes for the synthesis of aromatic azo compounds with CO using supported gold catalysts
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A facile and efficient catalytic system based on a mesostructured ceria-supported gold (Au/meso-CeO2) catalyst was developed for the synthesis of various aromatic azo compounds by the reductive coupling of the corresponding nitroaromatics, using CO as the sole deoxygenative reagent, under additive-free and mild reaction conditions.
- Li, Hai-Qian,Liu, Xiang,Zhang, Qi,Li, Shu-Shuang,Liu, Yong-Mei,He, He-Yong,Cao, Yong
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supporting information
p. 11217 - 11220
(2015/07/07)
-
- Photocatalytic reduction of nitroarenes to azo compounds over N-doped TiO2: Relationship between catalysts and chemical reactivity
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This work deals with selective reduction of aromatic nitro compounds to corresponding symmetrical substituted azo compounds using nitrogen-doped TiO2 nanoparticles as photocatalyst in the presence of a catalytic amount of formic acid. Various azo compounds containing additional reducible substituents including halogens, and carboxyl and phenol functions have been synthesized in a single step by use of this catalyst. The conversion was reasonably fast, clean, and high yielding at room temperature. A mechanism of formation for the azo compounds is proposed. The behavior of the N/TiO2 catalyst is of particular interest because this is the first time, as far as we know, that formation of azo compounds has been catalyzed by an N-doped TiO2 photocatalyst. Nitrogen-doped TiO2 was prepared by a simple modified sol-gel process with urea as nitrogen source. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy, and transmission electron microscopy. The chemical nature of N was identified by XPS as N-Ti-O in the anatase TiO2 lattice.
- Wang, Huqun,Yang, Xiaofeng,Xiong, Weifeng,Zhang, Zhimin
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p. 3981 - 3997
(2015/06/08)
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- Oxidation of aromatic anils by sodium perborate in aqueous acetic Acid Medium
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The kinetics of oxidation of 9 meta- and 15 para- substituted aromatic anils by sodium perborate were investigated in aqueous acetic acid medium. The reaction was second order with respect to aromatic anil and first order with respect to the sodium perborate. The increase of [H+] in this oxidation retards the rate of the reaction. The observed rate constant for the substituents were plotted against the Hammett constant, δ and a non-linear concave downward curve was obtained for the anils with substituents in the aniline moiety. The observed break in the log kobs versus δwas attributed to the transition state whereas the non-linear concave upward curve was observed for the substituents in the benzaldehyde moiety and a non-linear concave upward curve was observed for the substituents in the combination of aniline and benzaldehyde moiety. The electron withdrawing substituents fall on one side of the curve, having a negative ρvalue and the electron releasing substituents fall on the other side, with a positive ρvalue and a suitable mechanism was proposed.
- Venkatesh,Karunakaran
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p. 739 - 744
(2014/06/09)
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- Highly efficient synthesis of azos catalyzed by the common metal copper (0) through oxidative coupling reactions
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A facile and efficient approach to synthesize symmetric, asymmetric and bridged aromatic azo compounds (AAzos) from aromatic amines was developed by using red copper as catalyst. Despite numerous efforts towards the catalytic synthesis of symmetric and asymmetric AAzos derivatives, most reactions present certain drawbacks inhibiting their industrial applications, such as laborious multi-step processes, harsh reaction conditions and expensive reagents. And the synthesis of bridged azos had low yields before. With the presence of ammonium bromide as co-catalyst, pyridine as a ligand and molecular dioxygen as a sole oxidative reagent, red copper, a common and abundant metal in nature, exhibited unexpected catalytic activity towards the preparation of AAzos in high yields via one-step reaction, making this catalyst an attractive candidate for industrial and synthetic applications.
- Wang, Jiaqing,He, Jing,Zhi, Cong,Luo, Bin,Li, Xinming,Pan, Yue,Cao, Xueqin,Gu, Hongwei
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p. 16607 - 16611
(2014/05/06)
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- Graphene oxide supported MnO2 nanorods: An efficient heterogeneous catalyst for oxidation of aromatic amines to azo-compounds
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Graphene oxide supported MnO2 nanorods (GOnc), a composite material, has been synthesized and characterized by XRD, FE-SEM, EDX, BET surface area measurement, FTIR and Raman Spectroscopy. The composite material (GOnc) was found to be a highly efficient, reusable and cost effective heterogeneous catalyst for the one-pot, selective synthesis of azo-compounds from aromatic amines under an N2 atmosphere. After completion of the reaction, the catalyst is readily recovered by filtration and can be reused at least three times without significant loss in activity. This journal is
- Kumari, Shweta,Shekhar, Amiya,Pathak, Devendra D.
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p. 61187 - 61192
(2015/02/19)
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- Schiff base complexes of rare earth metal ions: Synthesis, characterization and catalytic activity for the oxidation of aniline and substituted anilines
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Several new lanthanide complexes of Pr(III), Sm(III), Gd(III), Tb(III), Er(III) and Yb(III) with the sodium salt of the Schiff base, 2-[(5-bromo-2-hydroxy-benzylidene)-amino]-5-methyl-pentanoic acid, derived from leucine and 5-bromosalicylaldehyde have been synthesized. These complexes having general formula [Ln(HL)(NO3)2(H2O)] ·NO3 were characterized by elemental analysis, UV-vis., FT-IR, EPR, Mass spectrometry and Thermal analysis. The FT-IR spectral data suggested that the ligand behaves as a tridentate ligand with one nitrogen and two oxygen donor atoms, sequence towards central metal ion. From the analytical data, the stoichiometry of the complexes was found to be 1:1 (metal:ligand). The physico-chemical data suggested eight coordination number for Ln(III) Schiff base complexes. Thermal behaviour (TGA/DTA) and fluorescence nature of the complexes were also studied. The Gd(III) Schiff base complex was found to be an efficient catalyst for the oxidation of aniline and substituted anilines under mild conditions.
- Lekha,Kanmani Raja,Rajagopal,Easwaramoorthy
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- NOVEL BIS-CHROMONE DERIVATIVES, METHODS FOR THEIR PREPARATION AND USES THEREOF
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The invention relates to novel bis-chromone derivatives, methods for their preparation and their therapeutic application, especially in the treatment or prevention of disease involving mast cell activation, such as allergic disease. Provided is a compound according to the general Formula (I).
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- An efficient catalyst-free and chemoselective synthesis of azobenzenes from nitrobenzenes
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NaOH mediated reaction of nitrobenzenes in EtOH was performed at 80 °C temperature affording azobenzenes in excellent yield. This methodology presents an easy synthesis of a wide variety of azo compounds from readily available nitrobenzene derivatives. This journal is
- Gund, Sitaram H.,Shelkar, Radheshyam S.,Nagarkar, Jayashree M.
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p. 42947 - 42951
(2015/02/19)
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- Gold-catalyzed direct hydrogenative coupling of nitroarenes to synthesize aromatic azo compounds
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The azo linkage is a prominent chemical motif which has found numerous applications in materials science, pharmaceuticals, and agrochemicals. Described herein is a sustainable heterogeneous-gold-catalyzed synthesis of azo arenes. Available nitroarenes are deoxygenated and linked selectively by the formation of N-N bonds using molecular H2 without any external additives. As a result of a unique and remarkable synergy between the metal and support, a facile surface-mediated condensation of nitroso and hydroxylamine intermediates is enabled, and the desired transformation proceeds in a highly selective manner under mild reaction conditions. The protocol tolerates a large variety of functional groups and offers a general and versatile method for the environmentally friendly synthesis of symmetric or asymmetric aromatic azo compounds.
- Liu, Xiang,Li, Hai-Qian,Ye, Sen,Liu, Yong-Mei,He, He-Yong,Cao, Yong
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supporting information
p. 7624 - 7628
(2014/08/05)
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- One-pot preparation of azobenzenes from nitrobenzenes by the combination of an indium-catalyzed reductive coupling and a subsequent oxidation
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We demonstrated how a reduction step with a reducing system comprised of In(OTf)3 and Et3SiH and a subsequent oxidation that occurred under an ambient (oxygen) atmosphere allowed the highly selective and catalytic conversion of aromatic nitro compounds into symmetrical or unsymmetrical azobenzene derivatives. This catalytic system displayed a tolerance for the functional groups on a benzene ring: an alkyl group, a halogen, an acetyl group, an ester, a nitrile group, an acetyl group, an ester moiety, and a sulfonamide group.
- Sakai, Norio,Asama, Shun,Anai, Satsuki,Konakahara, Takeo
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p. 2027 - 2033
(2014/03/21)
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- Kinetic investigation of oxidation of aromatic anils by potassium peroxymonosulfate in aqueous acidic medium
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The kinetics of oxidation of aromatic anils to benzaldehyde and azobenzene by potassium peroxymonosulfate has been studied in aqueous acetic acid medium. The low dielectric constant of the medium facilitates the reactivity. It has been found that the variation in the ionic strength of the reaction has a negligible effect on the rate. Similarly, polymerization was not observed when acrylonitrile was added to the reaction mixture. This observation rules out the formation of any free radical in the reaction. The added Mn(II) increases the rate of the reaction, which indicates the involvement of two-electron transfer. Highly negative ΔS# values indicate a structured transition state. The deviation of the Hammett plot was noted, and a concave downward curve was obtained for the anils with substituents in the aniline moiety. The observed break in the log kobs versus σ is attributed to the transition state whereas the concave upward curve was observed for the substituents in the benzaldehyde moiety and in the combination of aniline and benzaldehyde moieties, and a suitable mechanism was proposed.
- Venkatesh,Karunakaran
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p. 542 - 550
(2013/07/26)
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- Room temperature activation of oxygen by monodispersed metal nanoparticles: Oxidative dehydrogenative coupling of anilines for azobenzene syntheses
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It is highly challenging but desirable to develop efficient catalysts for the activation of oxygen under mild conditions. Here, we report that various monodispersed metal nanoparticles (Ag, Pt, Co, Cu, Ni, Pd, and Au) efficiently activated molecular oxygen under mild conditions, illustrated by the aerobic oxidation of anilines to form either symmetric or asymmetric aromatic azo compounds. This discovery indicates that exploiting the catalytic power of nanoparticles could enable sustainable chemistry suitable for important oxidation reactions.
- Cai, Shuangfei,Rong, Hongpan,Yu, Xiaofei,Liu, Xiangwen,Wang, Dingsheng,He, Wei,Li, Yadong
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p. 478 - 486
(2013/05/22)
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- Design, synthesis, and inhibitory activity of potent, photoswitchable mast cell activation inhibitors
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Allergic reactions affect millions of people worldwide. The need for new and effective antiallergic agents is evident, and insight into the underlying mechanisms that lead to allergic events is necessary. Herein, we report the design, synthesis, and activity of photoswitchable mast cell activation inhibitors. In mast cell degranulation assays, these inhibitors possess significantly greater potency than an original, chromone-based antiallergic agent. Furthermore, one of the photoswitchable inhibitors shows a significant difference in inhibitory activity between its two photoisomeric forms. Further optimization could ultimately lead to a photoswitchable compound suitable for studying mechanisms involved in allergic reactions in a novel manner, with activity addressable by light and with precise spatiotemporal control over events at the molecular level.
- Velema, Willem A.,Van Der Toorn, Marco,Szymanski, Wiktor,Feringa, Ben L.
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p. 4456 - 4464
(2013/07/19)
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- Kinetics and mechanism of meso-tetraphenyl-porphyriniron (III) chloride catalyzed oxidation of aniline and its substituents by oxone in aqueous acetic acid medium
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Metalloporphyrins are present naturally in cytochromes and hemoglobins. Perhaps the most interesting feature of heme-enzymes, such as cytochromes P450, is their ability to perform extremely difficult oxidations with high selectivity. The present work is undertaken with the aspiration of designing the mechanistic studies on meso-tetraphenylporphyriniron(III) chloride catalyzed oxidation of anilines by potassium peroxymonosulfate (oxone) in aqueous acetic acid medium. The study of oxidation with respect to the catalyst reveals that there is degradation of the catalyst. The concentration-protonated aniline (a less reactive species) increases due to the increase in [H+], which inhibits the rate of the reaction. The thermodynamic parameters for the oxidation have been determined and discussed. It confirms the Exner relationship and also the activation parameters to the isokinetic relationships. The oxone oxidation with 12 meta- and para-substituted anilines complies with the isokinetic relationship but not with any of the linear free energy relationships. The solvent interaction plays a major role in governing the reactivity. A suitable mechanism is proposed for this reaction.
- Raja,Karunakaran
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p. 580 - 587
(2013/08/23)
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- Mild, selective and switchable transfer reduction of nitroarenes catalyzed by supported gold nanoparticles
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A highly versatile and flexible gold-based catalytic system has been developed for the controlled and selective transfer reduction of nitroarene using 2-propanol as a convenient hydrogen source under mild conditions. Depending on the specific reaction conditions, multiple products including azoxyarenes, symmetric or asymmetric azoarenes and anilines can be obtained respectively via a controlled reduction of the nitro aromatics with good to excellent yields in the presence of a reusable mesostructured ceria-supported gold (Au/meso-CeO2) catalyst. The overall operational simplicity, high chemoselectivity, functional-group tolerance and reusability of the catalyst make this approach an attractive and reliable tool for organic and process chemists. The Royal Society of Chemistry.
- Liu, Xiang,Ye, Sen,Li, Hai-Qian,Liu, Yong-Mei,Cao, Yong,Fan, Kang-Nian
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p. 3200 - 3206
(2013/12/04)
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- Mg/Triethylammonium formate: A useful system for reductive dimerization of araldehydes into pinacols; Nitroarenes into azoarenes and azoarenes into hydrazoarenes
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Studies are reported which describes the effectiveness of triethylammonium formate in the presence of magnesium for the efficient intermolecular pinacol coupling using MeOH as solvent, Various aromatic carbonyls underwent smooth reductive coupling to give the corresponding I ,2-diols. A series of azo compounds were obtained by the reductive coupling of nitroaromatics while azo compounds were reduced to the corresponding hydrazoarenes by this system. There was no adverse effect on the other reducible and hydrogenolysable groups such as ether linkage, hydroxy and halogens. The reactions are clean, high yielding and inexpensive. All the reactions proceeded smoothly at ambient temperature.
- Pamar, M. Geeta,Govender,Muthusamy,Krause, Ruiw M.,Nanjundaswamy
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p. 969 - 974
(2014/03/21)
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- Light-triggered self-assembly of a dichromonyl compound in water
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External control over self-assembling structures is achieved by incorporating an azobenzene photoswitch into the structure of a dichromonyl compound. The self-assembly of dichromonyl compounds into fibers leads to the formation of a hydrogel and can be triggered with visible light. The Royal Society of Chemistry 2013.
- Velema, Willem A.,Stuart, Marc C. A.,Szymanski, Wiktor,Feringa, Ben L.
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supporting information
p. 5001 - 5003
(2013/07/04)
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- Meso-tetraphenylironporphyrin(III) chloride catalyzed oxidation of aniline and its substituents by m-chloroperbenzoic acid
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The most fascinating feature of heme-enzymes such as cytochromes P450 is their ability to carry out oxidations with high selectivity. Metalloporphyrin complexes are used as replicate compounds for cytochrome P450. A kinetic analysis has been carried out with the aim of understanding the mechanistic studies on oxidation of anilines by m-chloroperbenzoic acid catalyzed by meso-tetraphenylironporphyrin(III) chloride in aqueous acetic acid medium. The order of the reaction is found to be second order with respect to the substrate and first order with respect to the catalyst and oxidant. Product analysis proves that azobenzene is the sole product in the catalytic oxidation. The increase of [H+] in this oxidation retards the rate of the reaction. The effects of substituents on the oxidation rate are studied with 19 ortho-, meta- and para- substituted anilines at five different temperatures. The thermodynamic parameters for the oxidation have been determined and discussed. The catalysed m-chloroperbenzoic acid oxidation with substituted anilines fulfills the isokinetic relationship and Exner correlation but not to any of the linear free energy relationships. The solvent interaction also plays a major role in leading the reactivity. Based on the kinetic results and product analysis a probable mechanism is proposed.
- Raja,Karunakaran
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p. 1355 - 1360
(2013/06/27)
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- Highly efficient synthesis of aromatic azos catalyzed by unsupported ultra-thin Pt nanowires
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Aromatic azos were synthesized using unsupported ultra-thin platinum nanowires as catalysts under mild reaction conditions and the reaction mechanism was proposed.
- Hu, Lei,Cao, Xueqin,Chen, Liang,Zheng, Junwei,Lu, Jianmei,Sun, Xuhui,Gu, Hongwei
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supporting information; experimental part
p. 3445 - 3447
(2012/05/20)
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- Iron(III)-salen-H2O2 as a peroxidase model: Electron transfer reactions with anilines
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Iron(III)-salen complexes catalyze the H2O2 oxidation of various ring-substituted anilines in MeCN have been studied, and [O=Fe IV(salen)]+? is proposed as the active species. Study of the kinetics of the reaction by spectrophotometry shows the emergence of a new peak at 445 nm in the spectrum which corresponds to azobenzene. Further oxidation of azobenzene by H2O2 leads to the formation of azoxybenzene. ESI-MS studies also support the formation of these products. The rate constants for the oxidation of meta- and para-substituted anilines were determined from the rate of decay of oxidant as well as the rate of formation of azobenzene, and the reaction follows Michaelis-Menten kinetics. The rate data show a linear relationship with the Hammett σ constants and yield a ρ value of -1.1 to -2.4 for substituent variation in the anilines. A reaction mechanism involving electron transfer from aniline to [O=Fe(salen)] +? is proposed. The presence of axial ligands modulates the activity of the complex. Graphical Abstract: [Figure not available: see fulltext.]
- Aslam, Adhem Mohamed,Rajagopal, Seenivasan,Vairamani, Mariappanadar,Ravikumar, Maddula
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scheme or table
p. 751 - 759
(2012/07/01)
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- A highly active nano-palladium catalyst for the preparation of aromatic azos under mild conditions
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A worm-like Pd nanocatalyst has been prepared and used in the preparation of azo compounds from nitroaromatics under mild reaction conditions. This highly dispersible nano-Pd catalyst shows high activity toward the synthesis of both symmetric aromatic azo compounds and a range of asymmetric aromatic azo compounds.
- Hu, Lei,Cao, Xueqing,Shi, Linyan,Qi, Fenqiang,Guo, Zhiqiang,Lu, Jianmei,Gu, Hongwei
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supporting information; experimental part
p. 5640 - 5643
(2011/12/04)
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- Switchable selectivity during oxidation of anilines in a ball mill
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A solvent-free method for the direct oxidation of anilines to the corresponding azo and azoxy homocoupling products by using a planetary ball mill was developed. Various oxidants and grinding auxiliaries were tested and a variety of substituted anilines were investigated. It was possible to form chemoselectively either azo, azoxy, or the nitro compounds from reaction of aromatic anilines. The selectivity of the solvent-free reaction is switchable by applying a combination of oxidant and grinding auxiliary. Furthermore, a comparison with other methods of energy input (microwave, classical heating, and ultrasound) highlighted the advantages of the ball mill approach and its high energy efficiency. Grinding reactions: Highly efficient oxidative homocoupling of aromatic amines was performed under solvent-free conditions in a planetary ball mill (see scheme). The choice of solid oxidants and grinding auxiliaries allowed selective generation of the oxidized products. Other methods of energy input are compared with respect to reaction time and energy consumption.
- Thorwirth, Rico,Bernhardt, Franziska,Stolle, Achim,Ondruschka, Bernd,Asghari, Jila
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supporting information; experimental part
p. 13236 - 13242
(2011/02/21)
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