- 1,2-Eliminations in a novel reductive coupling of nitroarenes to give azoxy arenes by sodium bis(trimethylsilyl)amide
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(Chemical Equation Presented) Symmetric azoxy arenes were successfully prepared in one step from 2 equiv of the corresponding nitroarenes by use of sodium bis-(trimethylsilyl)amide as the deoxygenating agents in THF at 150°C in a sealed tube.
- Jih, Ru Hwu,Das, Asish R.,Chia, Wei Yang,Huang, Jiann-Jyh,Hsu, Ming-Hua
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- Zr(OH)4-Catalyzed Controllable Selective Oxidation of Anilines to Azoxybenzenes, Azobenzenes and Nitrosobenzenes
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The selective oxidation of aniline to metastable and valuable azoxybenzene, azobenzene or nitrosobenzene has important practical significance in organic synthesis. However, uncontrollable selectivity and laborious synthesis of the expensive required catalysts severely hinders the uptake of these reactions in industrial settings. Herein, we have pioneered the discovery of Zr(OH)4 as an efficient heterogeneous catalyst capable of the selective oxidation of aniline, using either peroxide or O2 as oxidant, to selectively obtain various azoxybenzenes, symmetric/unsymmetric azobenzenes, as well as nitrosobenzenes, by simply regulating the reaction solvent, without the need for additives. Mechanistic experiments and DFT calculations demonstrate that the activation of H2O2 and O2 is primarily achieved by the bridging hydroxyl and terminal hydroxyl groups of Zr(OH)4, respectively. The present work provides an economical and environmentally friendly strategy for the selective oxidation of aniline in industrial applications.
- Long, Yu,Luo, Nan,Ma, Jiantai,Qin, Jiaheng,Sun, Fangkun,Wang, Wei David,Zhou, Pan-Pan
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supporting information
(2021/12/09)
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- SO2F2-mediated oxidation of primary and tertiary amines with 30% aqueous H2O2 solution
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A highly efficient and selective oxidation of primary and tertiary amines employing SO2F2/H2O2/base system was described. Anilines were converted to the corresponding azoxybenzenes, while primary benzylamines were transformed into nitriles and secondary benzylamines were rearranged to amides. For tertiary amine substrates quinolines, isoquinolines and pyridines, their oxidation products were the corresponding N-oxides. The reaction conditions are very mild and just involve SO2F2, amines, 30% aqueous H2O2 solution, and inorganic base at room temperature. One unique advantage is that this oxidation system is just composed of inexpensive inorganic compounds without the use of any metal and organic compounds.
- Liao, Xudong,Zhou, Yi,Ai, Chengmei,Ye, Cuijiao,Chen, Guanghui,Yan, Zhaohua,Lin, Sen
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supporting information
(2021/11/01)
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- Selective Oxidation of Anilines to Azobenzenes and Azoxybenzenes by a Molecular Mo Oxide Catalyst
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Aromatic azo compounds, which play an important role in pharmaceutical and industrial applications, still face great challenges in synthesis. Herein, we report a molybdenum oxide compound, [N(C4H9)4]2[Mo6O19] (1), catalyzed selective oxidation of anilines with hydrogen peroxide as green oxidant. The oxidation of anilines can be realized in a fully selectively fashion to afford various symmetric/asymmetric azobenzene and azoxybenzene compounds, respectively, by changing additive and solvent, avoiding the use of stoichiometric metal oxidants. Preliminary mechanistic investigations suggest the intermediacy of highly active reactive and elusive Mo imido complexes.
- Han, Sheng,Cheng, Ying,Liu, Shanshan,Tao, Chaofu,Wang, Aiping,Wei, Wanguo,Yu, Han,Wei, Yongge
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supporting information
p. 6382 - 6385
(2021/02/09)
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- Iron-Catalyzed Hydrogen Transfer Reduction of Nitroarenes with Alcohols: Synthesis of Imines and Aza Heterocycles
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A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology. This protocol led specifically to imines in 30-91% yields, with a good functional group tolerance. Noticeably, starting from o-nitroaniline derivatives, in the presence of alcohols, benzimidazoles can be obtained in 64-72% yields when the reaction was performed with an additional oxidant, DDQ, and quinoxalines were prepared from 1,2-diols in 28-96% yields. This methodology, unprecedented at iron for imines, also provides a sustainable alternative for the preparation of quinoxalines and benzimidazoles.
- Wu, Jiajun,Darcel, Christophe
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supporting information
p. 1023 - 1036
(2021/01/09)
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- Light-Promoted C–N Coupling of Aryl Halides with Nitroarenes
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A photochemical C–N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step-economic extension to the widely used Buchwald–Hartwig C–N coupling reaction. The method tolerates coupling partners with steric-congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI/NiIII cycle, to a nitrosoarene intermediate.
- Li, Gang,Yang, Liu,Liu, Jian-Jun,Zhang, Wei,Cao, Rui,Wang, Chao,Zhang, Zunting,Xiao, Jianliang,Xue, Dong
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supporting information
p. 5230 - 5234
(2021/02/05)
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- Chemoselective electrochemical reduction of nitroarenes with gaseous ammonia
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Valuable aromatic nitrogen compounds can be synthesized by reduction of nitroarenes. Herein, we report electrochemical reduction of nitroarenes by a protocol that uses inert graphite felt as electrodes and ammonia as a reductant. Depending on the cell voltage and the solvent, the protocol can be used to obtain aromatic azoxy, azo, and hydrazo compounds, as well as aniline derivatives with high chemoselectivities. The protocol can be readily scaled up to >10 g with no decrease in yield, demonstrating its potential synthetic utility. A stepwise cathodic reduction pathway was proposed to account for the generations of products in turn.
- Chang, Liu,Li, Jin,Wu, Na,Cheng, Xu
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supporting information
p. 2468 - 2472
(2021/04/02)
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- Selective Photoinduced Reduction of Nitroarenes to N-Arylhydroxylamines
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We report the selective photoinduced reduction of nitroarenes to N-arylhydroxylamines. The present methodology facilitates this transformation in the absence of catalyst or additives and uses only light and methylhydrazine. This noncatalytic photoinduced transformation proceeds with a broad scope, excellent functional-group tolerance, and high yields. The potential of this protocol reflects on the selective and straightforward conversion of two general antibiotics, azomycin and chloramphenicol, to the bioactive hydroxylamine species.
- Kallitsakis, Michael G.,Ioannou, Dimitris I.,Terzidis, Michael A.,Kostakis, George E.,Lykakis, Ioannis N.
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supporting information
p. 4339 - 4343
(2020/06/08)
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- Efficient and Selective Oxidation of Aromatic Amines to Azoxy Derivatives over Aluminium and Gallium Oxide Catalysts with Nanorod Morphology
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Aluminium oxide and gallium oxide nanorods were identified as highly efficient heterogeneous catalysts for the selective oxidation of aromatic amines to azoxy compounds using hydrogen peroxide as environmentally friendly oxidant. This is the first report of the selective oxidation of aromatic amines to their azoxy derivatives without using transition metal catalysts. Among the tested transition-metal-free oxides, gallium oxide nanorods with small dimensions (9–52 nm length and 3–5 nm width) and fully accessible, high surface area (225 m2 g?1) displayed the best catalytic performance in terms of substrate versatility, activity and azoxybenzene selectivity. Furthermore, the catalyst loading, hydrogen peroxide type (aqueous or anhydrous), and the amount of solvent were tuned to optimise the catalytic performance, which allowed reaching almost full selectivity (98 %) towards azoxybenzene at high aniline conversion (94 %). Reusability tests showed that the gallium oxide nanorod catalyst can be recycled in consecutive runs with complete retention of the original activity and selectivity.
- Singh, Bhawan,Mandelli, Dalmo,Pescarmona, Paolo P.
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p. 593 - 601
(2019/11/13)
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- Preparation of azoxy benzene (by machine translation)
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[A] good workability and safety, cost, and, efficient production of the azoxy benzene azoxy benzene can be produced. [Solution] nitrobenzene ones, having the photocatalytic function with a dye, a reducing agent such as a fluorine resin or a transparent resin material is a mixed solution of 1 mm in diameter are inserted into the tube 4 does not inhibit the reaction, 4 LED lamp 5 emits visible from the outside of the tube moves within the tube 4 is provided with visible light within the tube 4 by a photocatalyst reaction mixed solution so as to obtain azoxy benzene compounds. Figure 2 [drawing] (by machine translation)
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Paragraph 0029; 0032
(2020/05/21)
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- Green and highly efficient approach for the reductive coupling of nitroarenes to azoxyarenes using the new mesoporous Fe3O4@SiO2@Co–Zr–Sb catalyst
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Efficient, green, simple and environmentally friendly approach for the straightforward reductive coupling of nitroarenes to the corresponding azoxyarenes has been developed in the presence of Fe3O4@SiO2@Co–Zr–Sb as a novel recyclable nanocatalyst. The Co–Zr–Sb trimetallic nanoparticles immobilized on silica-layered magnetite have been prepared by the co-precipitation method. The mesoporous catalyst has been characterized by FT-IR, SEM, EDX, VSM, TEM and XRD analyses. The chemoselective hydrogenation of nitrobenzenes was carried out successfully in refluxing water to afford the corresponding azoxybenzenes within 2–10?min in good to high yields. The reusability of the heterogeneous nanocatalyst has also been studied using the FT-IR and SEM analyses. The catalyst was utilized four times in sequential runs without significant loss of activity. The current research includes remarkable advantages of short reaction times, absence of hazardous organic solvents, mild reaction conditions, high yields, using water as a green solvent and the ability to utilize the recyclable nanomagnetic catalyst.
- Zeynizadeh, Behzad,Gilanizadeh, Masumeh
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p. 2969 - 2984
(2020/04/10)
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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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- Catalytic Selective Oxidative Coupling of Secondary N-Alkylanilines: An Approach to Azoxyarene
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Azoxyarenes are among important scaffolds in organic molecules. Direct oxidative coupling of primary anilines provides a concise fashion to construct them. However, whether these scaffolds can be prepared from secondary N-alkylanilines is not well explored. Here, we present a catalytic selective oxidative coupling of secondary N-alkylaniline to afford azoxyarene with tungsten catalyst under mild conditions. In addition, azoxy can be viewed as a bioisostere of alkene and amide. Several "azoxyarene analogues" of the corresponding bioactive alkenes and amides showed comparable promising anticancer activities.
- Ke, Lei,Zhu, Guirong,Qian, Hui,Xiang, Guangya,Chen, Qin,Chen, Zhilong
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p. 4008 - 4013
(2019/06/04)
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- Low-temperature catalytic oxidation of aniline to azoxybenzene over an Ag/Fe2O3 nanoparticle catalyst using H2O2 as an oxidant
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An in situ modified hydrothermal synthesis of Ag/Fe2O3 nanoparticles (NPs) and studies of their catalytic activity as a simple, eco-friendly and recyclable catalyst for one-pot conversion of aniline to azoxybenzene were performed. The as-synthesized nanostructured material was characterised by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), SEM-mapping, temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherms (BET), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), ultraviolet-visible spectroscopy (UV-vis) and vibrating sample magnetometer spectroscopy (VSM). The most active and recyclable catalyst with 2-5 nm diameters of the metallic Ag particles supported on 10-50 nm Fe2O3 nanoparticles was formed with a silver loading of 1.8 wt%. A high turnover number of ～592 was achieved with 92% conversion of aniline and 94% selectivity towards the target product azoxybenzene under atmospheric conditions. The effects of various reaction parameters including the reaction time, temperature and substrate to H2O2 molar ratio were screened and studied in detail. The results reveal the role of a synergistic effect between the surface Ag nanoparticles and Fe2O3 nanospheres for high catalytic activity.
- Paul, Bappi,Sharma, Sachin K.,Adak, Shubhadeep,Khatun, Rubina,Singh, Gurmeet,Das, Dipak,Joshi, Vedant,Bhandari, Sahil,Dhar, Siddhartha Sankar,Bal, Rajaram
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p. 8911 - 8918
(2019/06/18)
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- Niobium oxide prepared through a novel supercritical-CO2-assisted method as a highly active heterogeneous catalyst for the synthesis of azoxybenzene from aniline
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High-surface area Nb2O5 nanoparticles were synthesised by a novel supercritical-CO2-assisted method (Nb2O5-scCO2) and were applied for the first time as a heterogeneous catalyst in the oxidative coupling of aniline to azoxybenzene using the environmentally friendly H2O2 as the oxidant. The application of scCO2 in the synthesis of Nb2O5-scCO2 catalyst resulted in a significantly enhanced catalytic activity compared to a reference catalyst prepared without scCO2 (Nb2O5-Ref) or to commercial Nb2O5. Importantly, the Nb2O5-scCO2 catalyst achieved an aniline conversion of 86% (stoichiometric maximum of 93% with the employed aniline-to-H2O2 ratio of 1?:?1.4) with an azoxybenzene selectivity of 92% and with 95% efficiency in H2O2 utilisation in 45 min without requiring external heating (the reaction is exothermic) and with an extremely low catalyst loading (weight ratio between the catalyst and substrate, Rc/s = 0.005). This performance largely surpasses that of any other heterogeneous catalyst previously reported for this reaction. Additionally, the Nb2O5 catalyst displayed high activity also for substituted anilines (e.g. methyl or ethyl-anilines and para-anisidine) and was reused in consecutive runs without any loss of activity. Characterisation by means of N2-physisorption, XRD, FTIR and TEM allowed the correlation of the remarkable catalytic performance of Nb2O5-scCO2 to its higher surface area and discrete nanoparticle morphology compared to the aggregated larger particles constituting the material prepared without scCO2. A catalytic test in the presence of a radical scavenger proved that the reaction follows a radical pathway.
- Tao, Yehan,Singh, Bhawan,Jindal, Vanshika,Tang, Zhenchen,Pescarmona, Paolo P.
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p. 5852 - 5864
(2019/11/11)
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- Sustainable Protocol for the Reduction of Nitroarenes by Heterogeneous Au@SBA-15 with NaBH4 under Flow Conditions
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A gold-incorporated SBA-15 catalyst was prepared by a solvent-free ball-milling approach. The catalyst showed high reactivity and selectivity in the reduction of a variety of nitroarenes to anilines operating in absolute EtOH with NaBH4 as reducing agent. The catalyst was reused in batch conditions over five consecutive runs without any losses of activity or selectivity. Considering the high chemical stability and reusability of the catalytic system, a continuous-flow protocol was also investigated and defined to minimize the generation of waste and optimize the continuous reuse of the catalyst. Benefits of flow conditions were proven by turnover numbers that increased from 47.5 to 1902 and also by the minimization of both leaching (9.5 vs. 1 ppm) and E-factor values (8 vs. 23 in batch).
- Ferlin, Francesco,Giannoni, Tommaso,Zuliani, Alessio,Piermatti, Oriana,Luque, Rafael,Vaccaro, Luigi
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p. 3178 - 3184
(2019/02/19)
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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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p. 614 - 626
(2019/02/13)
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- Method for synthesizing oxidized azo compound through selective oxidation of aromatic amine
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The invention discloses a method for synthesizing an oxidized azo compound through selective oxidation of an aromatic amine, wherein an aromatic amine is used as a raw material, hydrogen peroxide is used as an oxidizing agent, a titanium-silicon molecular sieve or a metal modified titanium-silicon molecular sieve is used as a catalyst, and the aromatic amine is subjected to selective catalytic oxidation to prepare the corresponding oxidized azobenzene compound. According to the present invention, the method has advantages of environmental protection, good selectivity, high product yield, easyseparation and recycling of the catalyst, simple instrument required by the reaction, and easy operation.
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Paragraph 0027-0051; 0052-0055
(2019/02/13)
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- Room temperature catalytic reduction of nitrobenzene to azoxybenzene over one pot synthesised reduced graphene oxide decorated with Ag/ZnO nanocomposite
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We report herein, a one-pot synthetic route for the synthesis of reduced graphene oxide decorated Ag/ZnO nanocomposite and studied its catalytic activity as simple, recyclable and efficient catalyst for one-pot conversion of nitrobenzene to azoxybenzene. It was observed that 5–10 nm Ag-nanoparticles supported on 40–60 nm ZnO nanorod decorated on reduced graphene oxide was formed with a silver loading of 1.6 wt%. The effect of different reaction parameters were investigated and studied in detail. A nitrobenzene conversion of 96% with 98% selectivity of azoxybenzene was achieved without the use of any external additives.
- Paul, Bappi,Vadivel,Yadav, Nishant,Dhar, Siddhartha Sankar
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- Highly selective reduction of nitrobenzenes to azoxybenzenes with a copper catalyst
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A convenient protocol for highly selective delivery of azoxybenzenes from reduction of nitrobenzenes was developed by utilizing a copper catalyst. A variety of functional groups and substitution were well tolerated.
- Chen, Zhichao,Qiu, Yatao,Wu, Xiaoxing,Ni, Yong,Shen, Li,Wu, Jun,Jiang, Sheng
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supporting information
p. 1382 - 1384
(2018/03/06)
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- Efficient Solar-Driven Hydrogen Transfer by Bismuth-Based Photocatalyst with Engineered Basic Sites
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Photocatalytic organic conversions involving a hydrogen transfer (HT) step have attracted much attention, but the efficiency and selectivity under visible light irradiation still needs to be significantly enhanced. Here we have developed a noble metal-free, basic-site engineered bismuth oxybromide [Bi24O31Br10(OH)] that can accelerate the photocatalytic HT step in both reduction and oxidation reactions, i.e., nitrobenzene to azo/azoxybenzene, quinones to quinols, thiones to thiols, and alcohols to ketones under visible light irradiation and ambient conditions. Remarkably, quantum efficiencies of 42% and 32% for the nitrobenzene reduction can be reached under 410 and 450 nm irradiation, respectively. The Bi24O31Br10(OH) photocatalyst also exhibits excellent performance in up-scaling and stability under visible light and even solar irradiation, revealing economic potential for industrial applications.
- Dai, Yitao,Li, Chao,Shen, Yanbin,Zhu, Shujie,Hvid, Mathias S.,Wu, Lai-Chin,Skibsted, J?rgen,Li, Yongwang,Niemantsverdriet, J. W. Hans,Besenbacher, Flemming,Lock, Nina,Su, Ren
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supporting information
p. 16711 - 16719
(2018/12/11)
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- Reductive Denitration of Nitroarenes
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The Pd-catalyzed reductive denitration of nitroarenes has been achieved via a direct cleavage of the C-NO2 bonds. The catalytic conditions reported exhibit a broad substrate scope and good functional-group compatibility. Notably, the use of inexpensive propan-2-ol as a mild reductant suppresses the competitive formation of anilines, which are normally formed by other conventional reductions. Mechanistic studies have revealed that alcohols serve as efficient hydride donors in this reaction, possibly through β-hydride elimination from palladium alkoxides.
- Kashihara, Myuto,Yadav, M. Ramu,Nakao, Yoshiaki
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p. 1655 - 1658
(2018/03/23)
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- Organocatalytic oxidation of substituted anilines to azoxybenzenes and nitro compounds: Mechanistic studies excluding the involvement of a dioxirane intermediate
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An organocatalytic and environmentally friendly approach for the selective oxidation of substituted anilines was developed. Utilizing a 2,2,2-trifluoroacetophenone-mediated oxidation process, substituted anilines can be transformed into azoxybenzenes, while a simple treatment with MeCN and H2O2 leads to the corresponding nitro compounds, providing user-friendly protocols that can be easily scaled up. Various substitution patterns and functional groups were tolerated leading to products in high to excellent yields. Mechanistic studies utilizing HRMS provide clear evidence for the distinct mechanistic intermediates that are involved. This study constitutes an indirect proof excluding the involvement of a dioxirane intermediate in the green organocatalytic oxidation, utilizing 2,2,2-trifluoroacetophenone as the catalyst.
- Voutyritsa, Errika,Theodorou, Alexis,Kokotou, Maroula G.,Kokotos, Christoforos G.
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supporting information
p. 1291 - 1298
(2017/06/06)
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- A Highly Selective Amidation of Azoxybenzenes with Sulfonamides via Rhodium(III)-Catalyzed C-H Activation
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A new amidation of azoxybenzenes with sulfonamides catalyzed by a rhodium(III) salt has been developed. This sulfonamidation proceeds efficiently under mild reaction conditions to generate new C-N bonds through C-H bond activation and functionalization, affording the corresponding 2-sulfonamidoazoxybenzenes in good yields with high regioselectivity.
- Li, Hongji,Deng, Hong
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supporting information
p. 2711 - 2720
(2017/06/13)
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- Aromatic amine oxidation process for preparing aromatic liquid discharge method
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The invention relates to a preparation method for aromatic-azoxybenzene by oxidizing aromatic amine. According to the method, air or oxygen is used as an oxygen source, and aromatic amine is oxidized to be aromatic-azoxybenzene under the effect of metal oxide catalyst. The method has the advantage of high product yield and is easy to separate the catalyst.
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Paragraph 0014; 0015; 0016; 0017; 0018; 0019; 0020-0024
(2017/08/26)
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- Synthesis of Azoxybenzenes by Reductive Dimerization of Nitrosobenzene
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Herein we report an effective and simple preparation method of substituted azoxybenzenes by reductive dimerization of nitrosobenzenes. This procedure requires no additional catalyst/reagent and can be applied to substrates with a wide range of substitution patterns.
- Chen, Yu-Feng,Chen, Jing,Lin, Li-Jen,Chuang, Gary Jing
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p. 11626 - 11630
(2017/11/10)
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- Titania-Supported Gold Nanoparticles Catalyze the Selective Oxidation of Amines into Nitroso Compounds in the Presence of Hydrogen Peroxide
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In this article, the catalytic activity of titania-supported gold nanoparticles (Au/TiO2) was studied for the selective oxidation of amines into nitroso compounds using hydrogen peroxide (H2O2). Gold nanoparticles deposited on Degussa P25 polymorphs of titania (TiO2) have been found to promote the selective formation of a variety of nitroso arenes in high yields and selectivities, even in a large-scale synthesis. In contrast, alkyl amines are oxidized to the corresponding oximes under the examined conditions. Kinetic studies indicated that aryl amines substituted with electron-donating groups are oxidized faster than the corresponding amines bearing an electron-withdrawing functionality. A Hammett-type kinetic analysis of a range of para-X-substituted aryl amines implicates an electron transfer (ET) mechanism (ρ=-1.15) for oxidation reactions with concomitant formation of the corresponding N-aryl hydroxylamine as possible intermediate. We also show that the oxidation protocol of aryl amines in the presence of 1,3-cyclohexadiene leads in excellent yields to the corresponding hetero Diels-Alder adducts between the diene and the in situ formed nitrosoarenes.
- Fountoulaki, Stella,Gkizis, Petros L.,Symeonidis, Theodoros S.,Kaminioti, Eleni,Karina, Athanasia,Tamiolakis, Ioannis,Armatas, Gerasimos S.,Lykakis, Ioannis N.
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supporting information
p. 1500 - 1508
(2016/05/19)
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- Selective reduction of nitroaromatics to azoxy compounds on supported Ag-Cu alloy nanoparticles through visible light irradiation
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The selective hydrogenation of aromatic nitrocompounds to their corresponding azoxy compounds is challenging in organic synthesis, which are typically performed under harsh reaction conditions. The core issue involved in this reduction is to finely control the product selectivity. Herein, we report an efficient photocatalytic process using supported silver-copper alloy nanoparticles (Ag-Cu alloy NPs) to selectively transform nitrobenzene to azoxybenzene by visible light irradiation under green mild reaction conditions. Ag-Cu alloy NPs can absorb visible light, causing excited hot-electrons due to the localized surface plasmon resonance (LSPR) effect, and the excited electrons can activate the reactant molecule adsorbed on the NP surface to induce a reaction. The photocatalytic performance was affected by the Ag-Cu ratio, and the catalyst with an Ag-Cu molar ratio of 4-1 exhibited the optimal performance. Tuning the wavelength of incident light manipulated the product selectivity between azoxybenzene and aniline. Compared to pure Ag NPs, the alloying of Cu was found to be responsible for the product selectivity shifting from azobenzene to azoxybenzene. The reaction pathway was investigated to explain the selectivity difference and thus a tentative reaction pathway was proposed.
- Liu, Zhe,Huang, Yiming,Xiao, Qi,Zhu, Huaiyong
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supporting information
p. 817 - 825
(2016/02/12)
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- Room temperature selective oxidation of aniline to azoxybenzene over a silver supported tungsten oxide nanostructured catalyst
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Heterogeneous catalysts comprising silver nanoparticles supported on nanostructured tungsten oxide were applied for room temperature oxidative coupling of aniline to azoxybenzene, an important chemical intermediate and a chemical of industrial interest. The catalytic protocol features high activity and selectivity to the target product azoxybenzene with a turnover number of ～368. The catalyst was characterized by XRD, XPS, ICP-AES, FT-IR, TGA, EXAFS, SEM and TEM. The silver-tungsten nanomaterial acts as an excellent catalyst for selective oxidation of aniline to azoxybenzene using H2O2 as an oxidant. An aniline conversion of 87% with 91% selectivity of azoxybenzene was achieved without the use of any external additives. Moreover, a high stability and recyclability of the catalyst is also observed under the investigated conditions. This journal is
- Ghosh, Shilpi,Acharyya, Shankha S.,Sasaki, Takehiko,Bal, Rajaram
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p. 1867 - 1876
(2015/03/18)
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- Mild and selective catalytic oxidation of organic substrates by a carbon nanotube-rhodium nanohybrid
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A heterogeneous catalyst was assembled by stabilization of rhodium nanoparticles on carbon nanotubes. The nanohybrid was used for the catalytic aerobic oxidation of diverse substrates such as hydroquinones, hydroxylamines, silanes, hydrazines and thiols, at room temperature. The system proved very efficient on the investigated substrates and demonstrated high selectivity.
- Donck, Simon,Gravel, Edmond,Li, Alex,Prakash, Praveen,Shah, Nimesh,Leroy, Jocelyne,Li, Haiyan,Namboothiri, Irishi N. N.,Doris, Eric
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p. 4542 - 4546
(2015/09/01)
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- Ionic liquid effect: Selective aniline oxidative coupling to azoxybenzene by TiO2
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Simple commercially available TiO2 in ionic liquids (ILs) promotes the oxidative catalytic coupling of anilines to diazo compounds. For example, the reaction of aniline with molecular oxygen (5 bars) in the presence of TiO2 and functionalised imidazolium-based ILs affords azoxybenzene in up to 85% selectivity. The catalytic selectivity and activity are mainly related to the viscosity, oxygen solubility, and stability of the superoxide ion (O2-) and ionic species provided by the IL (IL effect). This effect is evident since most of the reactions performed in the presence of ILs gave as major products the azoxybenzene zwitterions. This is in opposition to that performed in toluene, which gave almost exclusively azobenzene.
- Qadir, Muhammad I.,Scholten, Jackson D.,Dupont, Jairton
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p. 1459 - 1462
(2015/04/14)
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- Ultrasound-accelerated selective oxidation of primary aromatic amines to azoxy derivatives with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane catalyzed by Preyssler acid-mediated nano-TiO2
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Preyssler-type heteropolyacid supported on TiO2 nanoparticles has been explored as an efficient catalyst in selective oxidation of primary aromatic amines to azoxy derivatives using trans-3,5-dihydroperoxy-3,5-dimethyl- 1,2-dioxolane as oxidant. The reactions proceeded smoothly under mild and green ultrasound-accelerated conditions to afford the products in high yields. The catalyst recovered from the reaction mixture exhibits long-term stability with no significant drop in its catalytic activity. Graphical abstract: [Figure not available: see fulltext.].
- Azarifar, Davood,Khatami, Seyed-Mola,Najminejad, Zohreh
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p. 587 - 592
(2014/04/03)
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- Mesoporous titania microspheres composed of exposed active faceted nanosheets and their catalytic activities for solvent-free synthesis of azoxybenzenes
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Mesoporous titania microspheres composed of nanosheets with exposed active facets were prepared by hydrothermal synthesis in the presence of hexafluorosilicic acid. They exhibited superior catalytic activity in the solvent-free synthesis of azoxybenzene by oxidation of aniline and could be used for 7 cycles with slight loss of activity. The Royal Society of Chemistry.
- Yang, Liuliu,Shi, Guodong,Ke, Xuebin,Shen, Ruwei,Zhang, Lixiong
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p. 1620 - 1624
(2014/03/21)
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- Copper nanoparticles on graphene support: An efficient photocatalyst for coupling of nitroaromatics in visible light
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Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm-2) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the N=O bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene. Green, light-assisted catalysis: Graphene-supported copper nanoparticles are used as photocatalysts. The photocatalysts can controllably reduce nitroaromatics to corresponding azoxy and azo compounds (see picture) under visible-light irradiation. Copyright
- Guo, Xiaoning,Hao, Caihong,Jin, Guoqiang,Zhu, Huai-Yong,Guo, Xiang-Yun
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p. 1973 - 1977
(2014/03/21)
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- Highly selective and controllable synthesis of arylhydroxylamines by the reduction of nitroarenes with an electron-withdrawing group using a new nitroreductase BaNTR1
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A new bacterial nitroreductase has been identified and used as a biocatalyst for the controllable reduction of a variety of nitroarenes with an electron-withdrawing group to the corresponding N-arylhydroxylamines under mild reaction conditions with excellent selectivity (>99%). This method therefore represents a green and efficient method for the synthesis of arylhydroxylamines.
- Nguyen-Tran, Hieu-Huy,Zheng, Gao-Wei,Qian, Xu-Hong,Xu, Jian-He
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supporting information
p. 2861 - 2864
(2014/03/21)
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- Silica encapsulated magnetic nanoparticles-supported Zn(II) nanocatalyst: A versatile integration of excellent reactivity and selectivity for the synthesis of azoxyarenes, combined with facile catalyst recovery and recyclability
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A novel and highly efficient zinc based nanocatalyst has been synthesized by covalent grafting of 2-acetylpyridine on amine functionalized silica@magnetite nanoparticles, followed by metallation with zinc acetate. The resulting nano-composite was found to be highly efficient for oxidation of various aromatic amines to give azoxyarenes. The prepared nanocatalyst was characterized by Electron microscopy techniques (SEM and TEM with EDS), X-ray diffraction (XRD), vibrational sampling magnetometer (VSM), Fourier transform infrared spectroscopy (FT-IR) and atomic absorption spectroscopy (AAS) techniques. High turnover number (TON), mild reaction conditions and high selectivity for azoxyarenes with sustained catalytic activity makes present protocol worthy and highly compliant as compared to the other non-magnetic heterogeneous catalytic system. The acquisition of this nanocatalyst is also exemplified by employing the catalyst in leaching and reusability test and the results from the tests showing negligible zinc leaching and recycling was achieved multiple times just by sequestering using an external magnet.
- Sharma,Monga, Yukti
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- A novel, efficient synthesis of N-aryl pyrroles via reaction of 1-boronodienes with arylnitroso compounds
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A one-pot hetero-Diels-Alder/ring contraction cascade is presented from the reaction of 1-boronodienes and arylnitroso derivatives to derive N-arylpyrroles in moderate to good yields (up to 82%).
- Tripoteau, Fabien,Eberlin, Ludovic,Fox, Mark A.,Carboni, Bertrand,Whiting, Andrew
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supporting information
p. 5414 - 5416
(2013/06/27)
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- Gold-catalyzed cyclization/oxidative [3+2] cycloadditions of 1,5-enynes with nitrosobenzenes without additional oxidants
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Golden control: The title reaction (see scheme) proceeds with high stereocontrol to generate the heterocyclic products in good yield. Experiments to probe the mechanism were performed. Copyright
- Chen, Chun-Hao,Tsai, Yen-Ching,Liu, Rai-Shung
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p. 4599 - 4603
(2013/05/21)
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- Nitrosobenzene as a hydrogen acceptor in rhodium catalysed dehydrogenation reactions of alcohols: Synthesis of aldehydes and azoxybenzenes
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Acids, esters and amides have to date been the only isolated products from the dehydrogenation of primary alcohols with [Rh(trop2N)(L)] (trop = 5-H-dibenzo[a,d]cyclohepten-5yl) type complexes. With the reported method the available product family is finally to aldehydes. Using nitrosobenzene as a hydrogen acceptor the aldehydes could be isolated in up to 96% yield with substrate to catalyst ratios of up to 1000. Nitrosobenzene was found to be reductively coupled to azoxybenzene under the reaction conditions. Several symmetrically substituted azoxybenzene derivatives could be isolated in generally high yields after 2 to 4 h reaction time using a low catalyst loading. The Royal Society of Chemistry 2012.
- Annen, Samuel P.,Gruetzmacher, Hansjoerg
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p. 14137 - 14145
(2013/01/15)
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- Ruthenium nanoparticle-catalyzed, controlled and chemoselective hydrogenation of nitroarenes using ethanol as a hydrogen source
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This communication describes a ruthenium nanoparticle-catalyzed reduction of nitroarenes giving azoxyarenes, azoarenes, or anilines in good to excellent yields using ethanol as a hydrogen source. Copyright
- Kim, Ju Hyun,Park, Ji Hoon,Chung, Young Keun,Park, Kang Hyun
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supporting information
p. 2412 - 2418
(2012/11/07)
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- Mesoporous nitrogen doped nano titania - A green photocatalyst for the effective reductive cleavage of azoxybenzenes to amines or 2-phenyl indazoles in methanol
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A new nitrogen precursor, hydrazine hydrate was used in the synthesis of nano-sized, N-doped TiO2 photocatalyst by a simple wet impregnation method. This photocatalyst was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), High resolution transmission electron microscope (HR-TEM), UV-vis diffuses reflectance spectra (DRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). XRD patterns show that the crystal structure of N-TiO2 resembles anatase phase of TiO2. The UV-vis spectra indicate an increase in absorption of visible light when compared to TiO2. Furthermore XPS analysis reveals the presence of the N atom as O-Ti-N linkage substituting the O atom in the TiO2 lattice and this causes a decrease in oxygen vacancies. N-TiO2 nanoparticles were used as a green and recyclable heterogeneous photocatalyst for rapid and efficient reductive cleavage of azoxybenzene into their corresponding amines or 2-phenylindazoles with methanol at room temperature under N2 atmosphere. Azoxybenzenes in neat methanol afforded anilines, while in aqueous methanol (20% water-80% methanol) they formed corresponding 2-phenyl indazoles. In both reductive cleavages, nano N-TiO2 is more effective than prepared TiO2, showing that the nitrogen doping could be an excellent choice to improve the photoactivity of TiO2.
- Selvam,Balachandran,Velmurugan,Swaminathan
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experimental part
p. 213 - 222
(2012/03/26)
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- Reduction of nitroarenes to azoxybenzenes by NaOH-PEG 400
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The reduction of nitroarenes to azoxybenzenes by NaOH-PEG 400 in benzene is described. The protocol is facile, economical, and effective.
- Liu, Yufang,Liu, Bo,Guo, Ailing,Dong, Zhenming,Jin, Shuo,Lu, Yun
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experimental part
p. 2201 - 2206
(2012/06/16)
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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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- Oxygen as moderator in the zinc-mediated reduction of aromatic nitro to azoxy compounds
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A simple and useful protocol for the reduction of nitro arenes to their corresponding azoxy derivatives by employing zinc and NH4Cl in a mixture of [bmim][BF4] and water is described. The selective reduction of nitro to azoxy is attributed to the hitherto unknown moderating effect of oxygen on zinc metal.
- Khan, Faiz Ahmed,Sudheer
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experimental part
p. 3394 - 3396
(2009/09/05)
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- Synthesis, oxidation and photophysical properties of novel derivatives of acyclic aromatic amines
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Conjugated acyclic arylamine derivatives, N-(4-methylphenyl)-N-(2-methyl-1- phenylpropyl)amine and N-(4-methoxyphenyl)-N-(2-methyl-1-phenylpropyl)amine, have been synthesized and characterized. Their photophysical properties have been investigated in polar methanol and non-polar cyclohexane solutions, and in PS and PMMA polymer matrices. The influence of the environment polarity as well as of the substituent in para-position of the aryl on the absorption, emission spectra and the fluorescence quantum yield has been studied. In the absorption and emission spectra, the observed absorption and emission band maxima were red shifted and the observed quantum yield was higher in the polar solution in comparison with the non-polar solution or polymer matrices. The distance of short- and long-wavelength absorption maxima in the methoxy derivative was larger and the emission band was red shifted in comparison with the methyl derivative. Chemical and photochemical oxidation of the prepared amines gives unstable nitroxides. High intramolecular quenching was observed in polymer matrix after photochemical oxidation of the amines.
- Kosa, Csaba,Mosnacek, Jaroslav,Bilesova, Adela,Kasak, Peter,Kronek, Juraj,Danko, Martin,Kollar, Jozef
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p. 1255 - 1268
(2008/09/20)
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- N,N,N′,N′-tetraalkylaminoazoxybenzene derivatives; convenient synthesis and mechanistic study
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N,N,N′,N′-tetraalkyaminoazoxybenzene derivatives were conveniently prepared by the coupling of N,N-dialkylnitrosoaniline in the presence of acetone and KOH. The reaction mechanism was proposed and investigated, and the structure of compound 3b was also confirmed by single crystal X-ray diffractometry.
- Lai, Long-Li,Chang, Yi-Ging,Hsu, Hui-Chu,Hsu, Shun-Ju,Luo, Dao-Wen
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p. 1639 - 1643
(2008/04/05)
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- Aqueous manganese-mediated reductive coupling of nitroarenes to azoxybenzenes
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Azoxy compounds have been prepared in good yields by reductive coupling of aromatic nitro compounds with manganese and a catalytic amount of acetic acid in aqueous conditions. Copyright Taylor & Francis Group, LLC.
- Dutta, Dilip K.
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p. 1903 - 1906
(2007/10/03)
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- Selective reduction of aromatic nitro compounds to azoxy compounds with zinc/aluminium chloride reagent
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Aromatic azoxy compounds have been prepared in good yields by the selective reduction of aromatic nitro compounds with Zn/AlCl3 reagent.
- Dutta, Dilip Kumar
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p. 672 - 673
(2007/10/03)
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- The newborn surface of dull metals in organic synthesis. Bismuth-mediated solvent-free one-step conversion of nitroarenes to azoxy- and azoarenes
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When milled together with bismuth shots, nitroarenes are readily converted to azoxy- and/or azoarenes depending on substrates and conditions employed. Simple extraction with organic solvent followed by evaporation of the resulting dark pasty solid gave the product in good yield.
- Wada, Shinobu,Urano, Mika,Suzuki, Hitomi
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p. 8254 - 8257
(2007/10/03)
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- Acidity and basicity of primary N-phenylnitramines: Catalytic effect of protons on the nitramine rearrangement
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Para-substituted N-phenylnitramines were prepared either by oxidation of diazonium salts or by nitration under alkaline or acidic conditions. Isotopic [15N-NO2] labelling indicated that the bands characteristic of the N-nitro group appear in the 1318-1323 and 1585-1607 cm-1 regions. In the nitrogen NMR spectra, the nitramino group gives two resonances at -193 ± 3 (NH) and -32 ± 3 ppm (NO2). The chemical shifts in proton and carbon NMR spectra are predictable, based on increments and the additivity rule. The spectral data indicate the lack of conjugation between the nitramino group and another substituent bound to the ring. It seems to contradict the well-known fact that substituents strongly (ρ = 4) influence the rate of nitramine rearrangement. The acidities of primary N-phenylnitramines (3.77 A B ≈ 21) are extremely low. Consequently, addition of protons to an intact nitramine molecule, as the preliminary step of the rearrangement, seems to be improbable. Migration of the N-nitro group precedes protonation; the latter process facilitates transformation of intermediates into stable final products. Copyright
- Daszkiewicz, Zdzislaw,Spaleniak, Grzegorz,Kyziol, Janusz B.
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p. 115 - 122
(2007/10/03)
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