- Continuous Flow Synthesis of Azoxybenzenes by Reductive Dimerization of Nitrosobenzenes with Gel-Bound Catalysts
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In the search for a new synthetic pathway for azoxybenzenes with different substitution patterns, an approach using a microfluidic reactor with gel-bound proline organocatalysts under continuous flow is presented. Herein the formation of differently substituted azoxybezenes by reductive dimerization of nitrosobenzenes within minutes at mild conditions in good to almost quantitative yields is described. The conversion within the microfluidic reactor is analyzed and used for optimizing and validating different parameters. The effects of the different functionalities on conversion, yield, and reaction times are analyzed in detail by NMR. The applicability of this reductive dimerization is demonstrated for a wide range of differently substituted nitrosobenzenes. The effects of these different functionalities on the structure of the obtained azoxyarenes are analyzed in detail by NMR and single-crystal X-ray diffraction. Based on these results, the turnover number and the turnover frequency were determined.
- Schmiegel, Carsten J.,Berg, Patrik,Obst, Franziska,Schoch, Roland,Appelhans, Dietmar,Kuckling, Dirk
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p. 1628 - 1636
(2021/03/15)
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- Understanding Mechanistic Differences between 3-Diazoindolin-2-Imines and N-Sulfonyl-1,2,3-Triazoles in the Rh2(II)-Catalyzed Reactions with Nitrosoarenes
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The employment of α-iminometallocarbenes to construct valuable N-containing compounds has attracted significant research interest. Herein, the nucleophilic addition of nitrosoarenes with the α-imino rhodium carbene species (I), which is derived from Rh2(II)-catalyzed denitrogenation of 3-diazoindolin-2-imines, to produce synthetically useful 2-iminoindolin-nitrones is described. Mechanistically, the N-attack of nitrosoarenes with the carbene site of I is proposed. For the analogous Rh2(II)-catalyzed reaction of nitrosoarenes with N-sulfonyl-1,2,3-triazoles reported by Li and co-workers (Org. Lett. 2014, 16, 6394), however, the O-attack of nitrosoarenes with the carbene site of α-imino rhodium carbene species (II) is more favorable to occur than the N-attack. The subsequent transformation to yield the product of N-acylamidines is rationalized based on computational studies. The mechanistic differences for the reactions of nitrosoarenes with α-imino rhodium carbene species I and II are discussed.
- Bao, Xiaoguang,Fu, Rui,Gao, Ke,Kou, Luyao,Zhou, Shaofang
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supporting information
p. 1565 - 1572
(2021/05/28)
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- Pt nanoparticles on Ti3C2T: X -based MXenes as efficient catalysts for the selective hydrogenation of nitroaromatic compounds to amines
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The development of Pt nanocatalysts for the selective hydrogenation of nitroaromatic compounds to the corresponding amines is of great significance to solve the drawbacks associated with a low reserve of Pt. Herein, we develop a protocol for the preparation of a Pt/titanium carbide-based MXene heterostructure for the selective reduction of nitroaromatic compounds. In the heterostructure, well-defined and nano-sized metallic Pt crystallites are uniformly decorated on Ti3C2Tx nanosheets using a mild reducing agent of ammonia borane without additional stabilizing agents. The selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) was employed as a model reaction to investigate the catalytic performance of the as-synthesized heterostructure, denoted as Pt/Ti3C2Tx-D-AB. Notably, this catalyst can catalyze the complete conversion of p-CNB to p-CAN with 99.5% selectivity, superior to that of Pt/Ti3C2Tx-D-SB synthesized with sodium borohydride. The high performance of the present catalytic system can be ascribed to the well-dispersed Pt nanoparticles, the abundant surface electron-efficient Pt(0), and the synergistic catalysis between Pt/Ti3C2Tx-D-AB and water. This catalyst also shows generality toward the selective hydrogenation of a series of nitroaromatic compounds to the corresponding amines with high efficiency. The present study provides a strategy to synthesize efficient catalysts for catalytic applications.
- Chen, Qian,Fan, Guangyin,Jiang, Weidong
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supporting information
p. 14914 - 14920
(2020/11/11)
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- Tungstate-supported silica-coated magnetite nanoparticles: a novel magnetically recoverable nanocatalyst for green synthesis of nitroso arenes
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Tungstate ion was heterogenized on the silica-coated magnetite nanoparticles and applied for the selective oxidation of anilines to nitroso arenes—with hydrogen peroxide/urea as oxidant in dimethyl carbonate as solvent—in moderate–good yields (40–96%). The catalyst was characterized using different techniques including Fourier-transform infrared spectroscopy, X-ray powder diffraction, vibrating sample magnetometry, scanning electron microscopy, energy dispersive X-ray and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst was easily recovered using an external magnet and reused for six times.
- Jadidi Nejad, Masoume,Yazdani, Elahe,Kazemi Miraki, Maryam,Heydari, Akbar
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p. 1575 - 1583
(2019/09/09)
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- A Photoswitchable Agonist for the Histamine H3 Receptor, a Prototypic Family A G-Protein-Coupled Receptor
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Spatiotemporal control over biochemical signaling processes involving G protein-coupled receptors (GPCRs) is highly desired for dissecting their complex intracellular signaling. We developed sixteen photoswitchable ligands for the human histamine H3 receptor (hH3R). Upon illumination, key compound 65 decreases its affinity for the hH3R by 8.5-fold and its potency in hH3R-mediated Gi protein activation by over 20-fold, with the trans and cis isomer both acting as full agonist. In real-time two-electrode voltage clamp experiments in Xenopus oocytes, 65 shows rapid light-induced modulation of hH3R activity. Ligand 65 shows good binding selectivity amongst the histamine receptor subfamily and has good photolytic stability. In all, 65 (VUF15000) is the first photoswitchable GPCR agonist confirmed to be modulated through its affinity and potency upon photoswitching while maintaining its intrinsic activity, rendering it a new chemical biology tool for spatiotemporal control of GPCR activation.
- Hauwert, Niels J.,Mocking, Tamara A. M.,Da Costa Pereira, Daniel,Lion, Ken,Huppelschoten, Yara,Vischer, Henry F.,De Esch, Iwan J. P.,Wijtmans, Maikel,Leurs, Rob
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supporting information
p. 4531 - 4535
(2019/03/07)
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- Novel Phenyldiazenyl Fibrate Analogues as PPAR α/γ/δ Pan-Agonists for the Amelioration of Metabolic Syndrome
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The development of PPARα/γ dual or PPARα/γ/δ pan-agonists could represent an efficacious approach for a simultaneous pharmacological intervention on carbohydrate and lipid metabolism. Two series of new phenyldiazenyl fibrate derivatives of GL479, a previously reported PPARα/γ dual agonist, were synthesized and tested. Compound 12a was identified as a PPAR pan-agonist with moderate and balanced activity on the three PPAR isoforms (α, γ, δ). Moreover, docking experiments showed that 12a adopts a different binding mode in PPARγ compared to PPARα or PPARδ, providing a structural basis for further structure-guided design of PPAR pan-agonists. The beneficial effects of 12a were evaluated both in vitro, on the expression of PPAR target key metabolic genes, and ex vivo in two rat tissue inflammatory models. The obtained results allow considering this compound as an interesting lead for the development of a new class of PPAR pan-agonists endowed with an activation profile exploitable for therapy of metabolic syndrome.
- Giampietro, Letizia,Laghezza, Antonio,Cerchia, Carmen,Florio, Rosalba,Recinella, Lucia,Capone, Fabio,Ammazzalorso, Alessandra,Bruno, Isabella,De Filippis, Barbara,Fantacuzzi, Marialuigia,Ferrante, Claudio,MacCallini, Cristina,Tortorella, Paolo,Verginelli, Fabio,Brunetti, Luigi,Cama, Alessandro,Amoroso, Rosa,Loiodice, Fulvio,Lavecchia, Antonio
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supporting information
p. 545 - 551
(2019/03/19)
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- Easily Accessible, Highly Potent, Photocontrolled Modulators of Bacterial Communication
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External control of bacterial communication—quorum sensing—allows for the regulation of a multitude of biological processes. Herein, we describe the development of a new synthetic methodology, as well as the characterization, photoisomerization, and biological evaluation of a privileged series of novel photoswitchable quorum-sensing agonists and antagonists. The presented method allows for the rapid and convenient synthesis of previously unknown photoswitchable agonists with up to 70% quorum-sensing induction and inhibitors reaching up to 40% inhibition, which significantly extends the level of photocontrol over bacterial communication achieved before. Remarkably, for the lead photoswitchable agonist, a >700-fold difference in activity was observed between the irradiated and non-irradiated forms, which allows for antagonism-to-agonism switching upon exposure to light, showing levels of control unprecedented in photopharmacology. Finally, utilizing this system, we were able to regulate toxin production in Pseudomonas aeruginosa with light. Photopharmacology is an emerging approach aimed at the regulation of biological function with light. Herein, the application of molecular photoswitches allows for the reversible switching between two distinct structural states of bioactive compounds. Bacterial communication (quorum sensing) is an interesting target for photopharmacology, from the perspective of both clinical and basic research, because of its implications for pathogenicity of bacteria and complex biological mechanism of action. By the novel synthesis and application of photoswitchable modulators, we were able to reversibly control bacterial communication with light. Remarkably, one of our lead compounds allows the control of bacterial communication with very high selectivity, switching from a quorum-sensing inhibitor to a quorum-sensing activator upon irradiation with light, which was further exemplified by the control of quorum-sensing-regulated toxin production in Pseudomonas aeruginosa. By applying the photopharmacological approach, bacterial communication can be controlled with light through the application of photoswitchable modulators. Interestingly, one of the lead photoswitchable modulators of bacterial communication, presented herein, shows a remarkable (>700-fold) difference in activity between the non-irradiated and irradiated states. The photoresponsive quorum-sensing modulators can be used to control toxin production in Pseudomonas aeruginosa and have a promising outlook as next-generation research tools.
- Hansen, Mickel J.,Hille, Jacques I.C.,Szymanski, Wiktor,Driessen, Arnold J.M.,Feringa, Ben L.
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supporting information
p. 1293 - 1301
(2019/05/06)
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- Enantioselective Oxidative Coupling of β-Ketocarbonyls and Anilines by Joint Chiral Primary Amine and Selenium Catalysis
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An enantioselective primary amine-catalyzed total N-selective nitroso aldol reaction (N-NA) was achieved through the oxidation of primary aromatic amines to the corresponding nitrosoarenes catalyzed by selenium reagents and 30% H2O2. This protocol provides a facile and highly efficient access to α-hydroxyamino carbonyls bearing chiral quaternary centers under exceedingly mild and green reaction conditions with high chemo-and enantiocontrol.
- Chen, Wanting,Wang, Yanni,Mi, Xueling,Luo, Sanzhong
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supporting information
p. 8178 - 8182
(2019/10/16)
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- A toolbox of molecular photoswitches to modulate the CXCR3 chemokine receptor with light
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We report a detailed structure–activity relationship for the scaffold of VUF16216, a compound we have previously communicated as a small-molecule efficacy photoswitch for the peptidergic chemokine GPCR CXCR3. A series of photoswitchable azobenzene ligands was prepared through various synthetic strategies and multistep syntheses. Photochemical and pharmacological properties were used to guide the design iterations. Investigations of positional and substituent effects reveal that halogen substituents on the ortho-position of the outer ring are preferred for conferring partial agonism on the cis form of the ligands. This effect could be expanded by an electron-donating group on the para-position of the central ring. A variety of efficacy differences between the trans and cis forms emerges from these compounds. Tool compounds VUF15888 (4d) and VUF16620 (6e) represent more subtle efficacy switches, while VUF16216 (6f) displays the largest efficacy switch, from antagonism to full agonism. The compound class disclosed here can aid in new photopharmacology studies of CXCR3 signaling.
- Gómez-Santacana, Xavier,De Munnik, Sabrina M.,Mocking, Tamara A.M.,Hauwert, Niels J.,Sun, Shanliang,Vijayachandran, Prashanna,De Esch, Iwan J.P.,Vischer, Henry F.,Wijtmans, Maikel,Leurs, Rob
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supporting information
p. 2509 - 2523
(2019/12/11)
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- Metal-Free Sequential C(sp2)-H/OH and C(sp3)-H Aminations of Nitrosoarenes and N-Heterocycles to Ring-Fused Imidazoles
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Hydrogen bond assisted ortho-selective C(sp2)-H amination of nitrosoarenes and subsequent α-C(sp3)-H functionalization of aliphatic amines is achieved under metal-free conditions. The annulation of nitrosoarenes and 2-hydroxy-C-nitroso compounds with N-heterocycles provides a facile excess to a wide range of biologically relevant ring-fused benzimidazoles and structurally novel polycyclic imidazoles, respectively. Nucleophilic aromatic hydrogen substitution (SNArH) was found to be preferred over classical SNAr reaction during the C(sp2)-H amination of halogenated nitrosoarenes.
- Purkait, Anisha,Roy, Subhra Kanti,Srivastava, Hemant Kumar,Jana, Chandan K.
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supporting information
p. 2540 - 2543
(2017/05/24)
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- Rh(III)-Catalyzed bilateral cyclization of aldehydes with nitrosos toward unsymmetrical acridines proceeding with C-H functionalization enabled by a transient directing group
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A Rh(iii)-catalyzed bilateral cyclization was developed for the efficient construction of acridines proceeding with C-H functionalization whereby in situ formation and removal of an imino transient directing group in the presence of catalytic amount of BnNH2 are achieved. In this transformation, a sequential Rh(iii)-catalyzed C-H amination, cyclization, and aromatization process was involved.
- Hu, Weiming,Zheng, Qingheng,Sun, Song,Cheng, Jiang
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supporting information
p. 6263 - 6266
(2017/07/07)
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- Palladium-catalyzed annulation of 2-(aryldiazenyl) aniline with dimethyl sulfoxide to access N-aryl-1H-benzo[d]imidazol-1-amine
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A palladium-catalyzed annulation of 2-(aryldiazenyl) aniline and dimethyl sulfoxide was developed to access N-aryl-1H-benzo[d]imidazol-1-amine in moderate to good yields. Activated by 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), DMSO served as a “[dbnd]CH[sbnd]” fragment during this procedure. It represents a facile pathway leading to benzimidazoles.
- Wang, Hepan,Sun, Song,Cheng, Jiang
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supporting information
p. 3875 - 3878
(2017/09/15)
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- In situ formation of gold nanoparticles on magnetic halloysite nanotubes via polydopamine chemistry for highly effective and recyclable catalysis?
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In this study, we present a simple and green approach to fabricate a magnetic halloysite nanotube (MHNT) supported Au nanoparticle (NP) composite (MHNTs–PDA–Au) with a polydopamine functional coating for highly effective and recyclable catalysis. The fabrication of MHNTs–PDA–Au involves decoration of Fe3O4 NPs on HNTs via a one-step co-precipitation method, deposition of a polydopamine layer on the MHNTs and subsequent in situ reduction of Au NPs via polydopamine chemistry. All the processes are simple and eco-friendly without use of additional toxic reagents and complicated treatment. The obtained MHNTs–PDA–Au composite exhibits excellent and versatile catalytic activity toward the reduction of various nitrobenzene derivatives and methylene blue dye when only trace amounts of Au catalyst are used. In addition, the catalytic system can be easily recycled for several cycles based on its good magnetic properties. The synergistic combination of MHNTs, polydopamine coating and metal NPs offers a versatile platform for design of natural HNT based composite materials and will expand the applications of HNTs in heterogeneous catalysis, water purification and green chemistry.
- Wei, Qiangbing,Shi, Ruirong,Lu, Dedai,Lei, Ziqiang
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p. 29245 - 29253
(2018/05/31)
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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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- Azopyridine-imidacloprid derivatives as photoresponsive neonicotinoids
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A series of imidacloprid derivatives containing an azopyridine motif as a photoswitchable functional group were designed and synthesized. The new version of photoresponsive imidacloprid analogues showed improved solubility in comparison with their azobenzene analogues. 1.2 to 2-fold activity difference was observed for these azopyridine-imidacloprids against house fly (Musca domestica) and cowpea aphid (Aphis craccivora) upon irradiation.
- Li, Shen,Song, Run-Jiang,Wang, Dong-Hui,Tian, Xue,Shao, Xu-Sheng,Li, Zhong
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p. 635 - 639
(2016/05/19)
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- Synthesis of 1H-Indazoles from Imidates and Nitrosobenzenes via Synergistic Rhodium/Copper Catalysis
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Nitrosobenzenes have been used as a convenient aminating reagent for the efficient synthesis of 1H-indazoles via rhodium and copper catalyzed C-H activation and C-N/N-N coupling. The reaction occurred under redox-neutral conditions with high efficiency and functional group tolerance. Moreover, a rhodacyclic imidate complex has been identified as a key intermediate.
- Wang, Qiang,Li, Xingwei
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supporting information
p. 2102 - 2105
(2016/06/01)
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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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- Para-Selective Halogenation of Nitrosoarenes with Copper(II) Halides
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The para-selective direct bromination and chlorination of nitrosoarenes with copper(II) bromide and chloride is reported. Under mild reaction conditions, a range of halogenated arylnitroso compounds are obtained in moderate to good yields with high regioselectivity. Additionally, the versatility of the method is demonstrated by the development of a one-pot procedure to obtain the corresponding para-halogenated aniline- and nitrobenzene derivatives.
- Van Der Werf, Angela,Selander, Nicklas
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supporting information
p. 6210 - 6213
(2016/01/09)
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- Ipso-Nitrosation of arylboronic acids with chlorotrimethylsilane and sodium nitrite
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Nitroso compounds are versatile reagents in synthetic organic chemistry. Herein, we disclose a feasible protocol for the ipso-nitrosation of aryl boronic acids using chlorotrimethylsilane-sodium nitrite unison as nitrosation reagent system.
- Prakash, G.K. Surya,Gurung, Laxman,Schmid, Philipp Christoph,Wang, Fang,Thomas, Tisa Elizabeth,Panja, Chiradeep,Mathew, Thomas,Olah, George A.
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p. 1975 - 1978
(2014/04/03)
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- Pt-NH2-Fe3O4 catalyst with excellent catalytic performance for hydrogenation of nitroarenes in aqueous medium
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Catalytic hydrogenation of aromatic nitro compounds was carried out in neat water with Pt nanoparticles deposited on surface amine-functionalized magnetite. The hydrophilic Pt-NH2-Fe3O4 catalyst exhibited excellent activity as well as superior selectivity to the corresponding amines. 99.9% yield of p-chloroaniline (p-CAN) was obtained at 303 K under an H2 atmosphere in aqueous media; the turnover frequency value reached 500 h-1 in the absence of any additives or promoters. Furthermore, the novel nanocomposites can be readily isolated from the reaction system by a magnet and recycled at least six times without any loss in activity.
- Fan, Guangyin,Wang, Yinhu
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p. 967 - 973
(2014/04/03)
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- Mechanochemically induced cross-dimerizations of nitrosobenzenes. Kinetics and solid-state isotope effects
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Mechanical treatment (milling) of crystals of aromatic nitroso dimers (azodioxides) induces their dissociation and cross-dimerizations. The mechanisms of these processes are discussed on the basis of kinetic studies and the solid-state 15 N kinetic isotope effect, which is measured for the first time. By comparison with analogous processes in cocrystals and in melts, it appears that the reactions follow similar mechanism in which the surface deformations play the crucial role. The system can also be used as a model for a more general conceptual study of solid-state reaction mechanisms. Copyright
- Maganjic, Ana,Solic, Ivan,Milovac, Srd Strok Signan,Halasz, Ivan,Biljan, Ivana,Vancik, Hrvoj
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p. 177 - 182
(2014/03/21)
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- Mechanosynthesis of nitrosobenzenes: A proof-of-principle study in combining solvent-free synthesis with solvent-free separations
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Mechanochemical Oxone oxidation of selected para-substituted anilines was used as a rapid and solvent-free route to nitrosobenzenes; besides avoiding bulk solvents and short reaction times, this method exploits high vapour pressures of nitrosobenzenes for the solvent-free separation of the product by sublimation, demonstrating an entirely solvent-free route to chemical synthesis and product isolation. The Royal Society of Chemistry.
- Huskic, Igor,Halasz, Ivan,Friscic, Tomislav,Vancik, Hrvoj
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supporting information
p. 1597 - 1600
(2013/02/23)
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- Organic-inorganic hybrid SiO2 supported gold nanoparticles: Facile preparation and catalytic hydrogenation of aromatic nitro compounds
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Highly dispersed gold nanoparticles supported on organic-inorganic hybrid silica have been successfully prepared through a novel and facile approach. In the process, 3-aminopropyltriethoxysilane was hydrolyzed in HCHO aqueous solution to prepare silica with organic functional groups (-SiCH 2CH2CH2NHCH2OH) formed through the reaction between -NH2 and HCHO, then the silica reacted with HAuCl4 in aqueous solution. Due to the reducibility of -SiCH2CH 2CH2NHCH2OH, the gold precursor was in situ reduced on the silica. The materials were characterized by powder X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy techniques. The results indicated Au nanoparticles were highly dispersed on silica with an average particles size 1.8 ± 0.5 nm. The asobtained Au/SiO2-org exhibited good catalytic activity and stability for liquid phase catalytic hydrogenation of aromatic nitro compounds with H2.
- Tan, Xiaoying,Zhang, Zhixin,Xiao, Zihui,Xu, Qiang,Liang, Changhai,Wang, Xinkui
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experimental part
p. 788 - 793
(2012/08/28)
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- Nitrosation of aryl and heteroaryltrifluoroborates with nitrosonium tetrafluoroborate
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Organotrifluoroborates have emerged as an alternative to toxic and air- and moisture-sensitive organometallic species for the synthesis of functionalized aryl and heteroaryl compounds. It has been shown that the trifluoroborate moiety can be easily converted into a variety of different substituents in a late synthetic stage. In this paper, we disclose a mild, selective, and convenient method for the ipso-nitrosation of organotrifluoroborates using nitrosonium tetrafluoroborate (NOBF4). Aryl- and heteroaryltrifluoroborates were converted into the corresponding nitroso products in good to excellent yields. This method proved to be tolerant of a broad range of functional groups.
- Molander, Gary A.,Cavalcanti, Livia N.
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experimental part
p. 4402 - 4413
(2012/06/18)
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- Control of the equilibrium between 2-phosphinoazobenzenes and inner phosphonium salts by heat, solvent, acid, and photoirradiation
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Several 2-phosphinoazobenzenes, which are in equilibrium with inner phosphonium salts, were synthesized. Effects of substituents, solvents, and acidic additives on their equilibria are described. Thermodynamic parameters of the equilibria in various solvents suggest that the acceptor character of the solvents is mainly responsible for the solvent effects. Addition of phenols changed the equilibria depending on their acidity. Substituents at the 4- and 4′-positions of the azobenzene also affected the equilibrium constants, which shifted the equilibrium toward the phosphonium salt in the order of their electron-withdrawing ability. Photoisomerization of the 2-phosphinoazobenzenes bearing electron-donating substituents at the 4- and 4′-positions, which shifted the equilibrium toward the 2-phosphinoazobenzene, proceeded successfully. While the phosphonium salt in equilibrium with the (E)-isomer of the 2-phosphinoazobenzene was protonated by perchlorophenol, the (Z)-isomer did not react with a proton source because it could not take on the form of an inner phosphonium salt. Thus, the properties and reactivity of the inner phosphonium salts in equilibrium with the phosphines can be successfully controlled by photoirradiation.
- Yamamura, Masaki,Kano, Naokazu,Kawashima, Takayuki
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experimental part
p. 110 - 123
(2012/03/07)
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- Photothermal reactions of nitrosobenzene and halonitrosobenzenes in solid-state
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Photothermal reactions of the dimers of nitrosobenzene, m-chloronitrosobenzene, and p-chloronitrosobenzene were studied in solid-state by IR spectroscopy at low temperatures and by X-ray powder diffraction. It was found for the first time that photothermal cycle (photolytic dissociation fol-lowed by thermal dimerization) could successively be performed also with Z-configured dimeric nitroso-benzene. Halonitrosobenzenes dimers with E-configuration afforded different photo behavior depending on the po-sition of halogen atom on the benzene ring: while m-halonitrosobenzenes do not dissociate under UV ir-radiation, p-chloronitrosobenzene, as well as previously studied p-bromonitrosobenzene photolyses very efficiently with recovering of the original crystal phase. Kinetics of thermal dimerization was measured in solid-state, and it was found that the reaction phase transformation occurs as a two-dimensional growth through the crystal.
- Knezevic, Anamarija,Medancic, Tina,Milovac, Srdan,Biljan, Ivana,Halasz, Ivan,Vancik, Hrvoj
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scheme or table
p. 21 - 24
(2012/02/15)
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- Reduction of nitrosobenzenes to azoarenes with SmI2
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A novel method was developed to synthesise azoarenes from nitrosobenzenes under mild conditions. Samarium (II) iodine was used to achieve the N-N coupling. The method also provides evidence for the proposed mechanism involved in the reduction of nitro compounds to the amines with SmI2.
- Ye, Wei,Ding, Wenbo,Hu, Zhang,Yu, Yongping,Zou, Hongbin
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body text
p. 214 - 215
(2010/07/08)
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- Nitrosobenzene cross-dimerization: Structural selectivity in solution and in solid state
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Possibility of nitrosobenzenes to form dimeric molecular structures (azodioxides) is used as a model for intermolecular selectivity investigations in solution as well as in solid state. Cross-dimerization of different combinations of p- and m-substituted nitrosobenzene pairs was studied by variable temperature 1H NMR, solid-state NMR (CP MAS), IR, and ab initio calculations. It is evident that p-nitronitrosobenzene behaves nonselectively because it forms dimers with all the studied nitrosobenzene partners. In contrast, p-methoxynitrosobenzene in most cases does not form dimers. The evidence that ability to form dimers is different in solution than in the solid state can be explained by influence of molecular arrangements in the crystal lattice.
- Biljan, Ivana,Cvjetojevic, Gorana,Smrecki, Vilko,Novak, Predrag,Mali, Gregor,Plavec, Janez,Babic, Darko,Mihalic, Zlatko,Vancik, Hrvoj
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body text
p. 22 - 26
(2010/09/16)
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- Preparation of azobenzenealkanethiols for self-assembled monolayers with photoswitchable properties
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A series of azobenzenealkanethiol compounds with the structure p-RC 6H4N=NC6H4(CH2) nSH (n = 3, 4) was synthesized using a divergent strategy with the two anilines H2NC6H4(CH2) nSAc as central compounds. This strategy provides fast access to a broad variety of the respective azobenzenethiols without (note!) an oxygen atom in the alkyl chain, thus permitting the self-assembly of these compounds onto gold in a predictable conformation, also taking advantage of the previously found odd-even effect in aromatic-aliphatic hybrid systems. Initial experiments indicate that all of these molecules indeed form dense monolayers, in which the orientation of the azobenzene unit is determined by the number of methylene groups in the aliphatic part of the molecules. CSIRO 2010.
- Krakert, Simone,Terfort, Andreas
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body text
p. 303 - 314
(2011/06/23)
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- N-Oxidation of arylamines to nitrosobenzenes using chloroperoxidase purified from Musa paradisiaca stem juice
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N-Oxidation of arylamines to their corresponding nitrosobenzenes using a new chloroperoxidase purified from Musa paradisiaca stem juice has been examined. The enzymatic characteristics of the stem chloroperoxidase using 4-chloroaniline as substrate were determined. The Km values for 4-chloroaniline and H2O2 were 770 μM and 154 μM respectively, while the pH and temperature optima were 4.4 and 30°C respectively. The substrate specificities of the enzyme for the arylamines 3,4-dichloroamine, p-aminobenzoic acid, p-toluidine, p-anisidine, m-anisidine, p-aminophenol, o-aminophenol and m-aminophenol have been characterized. The feasibility of using concentrated M. paradisiaca stem juice for the specific conversion of 4-chloroaniline to 4-chloronitrosobenzene has been demonstrated. This enzyme can be used for the N-oxidation of other arylamines.
- Yadav, Pratibha,Sharma, Jitendra K.,K. Singh, Vinod,Yadav, Kapil D. S.
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body text
p. 222 - 226
(2011/12/04)
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- Influence of 1,3-dichloroacetone on the regularities of decay of arylnitroso oxides
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The decay kinetics of isomeric forms of a series of arylnitroso oxides in the presence of 1,3-dichloroacetone in acetonitrile was studied by the flash photolysis technique. The regularities observed are explained by the complex formation between the molecules of nitroso oxide and additive.
- Chainikova,Safiullin
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p. 2437 - 2442
(2014/05/06)
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- Multiphase oxidation of aniline to nitrosobenzene with hydrogen peroxide catalyzed by heteropolyacids
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Keggin-type heteropolyacids have been used as catalyst for high-yielding oxidation reactions in multiphase conditions. This simple and efficient procedure promoted the conversion of anilines to the corresponding nitroso and nitro derivatives. In comparison with homogeneous system the oxidation from anilines to nitroso compounds and nitro compounds were more effective and the solvents used were not toxic. Georg Thieme Verlag Stuttgart.
- Tundo,Romanelli,Vázquez,Loris,Aricò
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experimental part
p. 967 - 970
(2009/04/06)
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- A highly stereoselective organocatalytic tandem aminoxylation/aza-Michael reaction for the synthesis of tetrahydro-1,2-oxazines
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(Chemical Equation Presented) A facile stereoselective synthesis of multifunctionalized tetrahydro-1,2-oxazines (THOs) has been achieved by the organocatalyzed asymmetric tandem α-aminoxylation/aza-Michael reaction for the C-O/C -N bond formations in moderate to good yields with excellent diastereo- (>99:1 dr) and enantioselectivities (92% to >99% ee).
- Zhu, Di,Lu, Min,Chua, Pei Juan,Tan, Bin,Wang, Fei,Yang, Xinhao,Zhong, Guofu
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supporting information; experimental part
p. 4585 - 4588
(2009/05/13)
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- In situ generation of nitroso compounds from catalytic hydrogen peroxide oxidation of primary aromatic amines and their one-pot use in hetero-Diels-Alder reactions
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A method for in situ generation of nitroso compounds from organoselenium-catalyzed oxidation of anilines by hydrogen peroxide was developed. The generated nitroso compounds were subsequently used in hetero-Diels-Alder reactions. A variety of oxazines were synthesized in reasonable to good yields by this one-pot procedure using primary aromatic amines with different substituents and various conjugated dienes. This strategy might facilitate the current methodologies for nitroso chemistry since no isolation or purification of the nitroso compounds is required. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Zhao, Dongbo,Johansson, Mikael,Baeckvall, Jan-E.
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p. 4431 - 4436
(2008/04/13)
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- Tungsten- and molybdenum-based coordination polymer-catalyzed N-oxidation of primary aromatic amines with aqueous hydrogen peroxide
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Recyclable tungsten- and molybdenum-based coordination polymers efficiently catalyzed the oxidation of primary aromatic amines to the corresponding nitroso derivatives with 30% aqueous hydrogen peroxide in high yields at room temperature.
- Bordoloi, Ankur,Halligudi
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p. 2085 - 2088
(2008/09/18)
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- Simple preparation of nitroso benzenes and nitro benzenes by oxidation of anilines with H2O2 catalysed with molybdenum salts
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Nitroso arenes 2a-k are prepared in 53-80% yield from anilines 1a-k by oxidation with H2O2 catalysed with MoO3/KOH, ammonium molybdate or other molybdenum salts. Further oxidation to nitro arenes 3a,d j in 66-90% is also described.
- Defoin, Albert
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p. 706 - 710
(2007/10/03)
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- Reactions of nitrosoarenes containing electron-withdrawing substituents with coordinated CO. Synthesis and structure of complexes Pd2(OAc) 2(p-ClC6H4N[p-ClC6H 3NO])2 and Pd2(OAc)2(o-ClC 6H4N[o-ClC6H3NO])2
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The reaction of tetranuclear Pd4(μ-COOCH3) 4(μ-CO)4 cluster (1a) with p- and o- chloronitrosobenzenes was found to give dinuclear nitrosoamide complexes, Pd2(OAc)2(p-ClC6H4N[p-ClC 6H3NO])2 (4) and Pd2(OAc) 2(o-ClC6H4N[o-ClC6H 3NO])2 (5), respectively. The formation of complexes 4 and 5 is accompanied by evolution of CO2, resulting from oxidation of CO coordinated in cluster 1. Complexes 4 and 5 were characterized by elemental analysis and IR and 1H NMR spectroscopy; their structures were studied by EXAFS. The reactions of dinuclear complex 4 with molecular hydrogen and CO were studied. The major products of reduction of 4 with hydrogen include metallic palladium, acetic acid, cyclohexanone, and molecular nitrogen. Treatment of complex 4 with CO under mild conditions (1 atm, 20°C) affords p-chlorophenyl isocyanate.
- Orlova,Stromnova,Kazyul'kin,Boganova,Kochubey,Novgorodov
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p. 819 - 824
(2007/10/03)
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- An exceptionally stable Ti superoxide radical ion: A novel heterogeneous catalyst for the direct conversion of aromatic primary amines to nitro compounds
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A matrix-bound superoxide radical anion, generated by treating Ti(OR)4 (R =iPr, nBu) with H2O2, is a selective heterogeneous catalyst for the oxidation of anilines to the corresponding nitroarenes with 50 % aqueous H2O2 [Eq. (1)]. Yields of 82-98 % are obtained, even with anilines bearing electron-withdrawing substituents (R = NO2, COOH).
- Dewkar, Gajanan K.,Nikalje, Milind D.,Ali, Iliyas Sayyed,Paraskar, Abhimanyu S.,Jagtap,Sudalai
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p. 405 - 408
(2007/10/03)
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- Nonlinear Hammett relationships in the reaction of peroxomonosulfate anion (HOOSO-3) with meta-and para-substituted anilines in alkaline medium
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The HOOSO-3 oxidation of eleven meta-and para-substituted anilines to the corresponding nitrosobenzenes at pH ≈ 11 was characterized by the rate equation v = kK[OX][An]/(1 + K[An]). Formation constant of the reactive intermediate and its rate of decomposition were evaluated separately for ascertaining the structure-reactivity relationships. Under the experimental conditions the dianion, -O-O-SO-3 is probably the effective electrophile. Kinetic data can be rationalized by a bimolecular process which involves the attack of nucleophilic nitrogen atom on the peroxidic oxygen. The highlight of the study is the opposite curvatures observed in the nonlinear Hammett plots of first-order rate constant k and the "equilibrium" constant K, being concave downward and upward, respectively.
- Meenakshisundaram, Subbiah,Sockalingam, Ramanathan
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p. 897 - 911
(2007/10/03)
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- Reaction of dimethyldioxirane with aniline hydrohalides
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Oxidation of aromatic amine hydrohalides (aniline hydrochloride, hydrobromide, and hydrofluoride; 4-methylaniline hydrochloride and hydrobromide; 3-methylaniline and N,N-diethylaniline hydrochlorides) with dimethyldioxirane was studied. The product composition was analyzed in relation to the reactant ratio.
- Ivanova,Grabovskii,Kabal'nova,Shereshovets
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p. 2101 - 2105
(2007/10/03)
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- Structural investigations of C-nitrosobenzenes. Part 1. Solution state 1H NMR studies
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Ambient and low temperature 1H NMR spectra of a wide range of 3- and 4-monosubstituted, and some di- and tri-substituted C-nitrosobenzenes have enabled -N=O substituent constants for the static and rotating ring molecules to be calculated. This has provided information on the shielding anisotropy of the N=O group which in turn leads to the firm identification of the monomeric and dimeric solution species. In all cases lowering the solution temperature enhances the relative populations of dimers to monomers, with the (Z)-azodioxy dimer being preferred over the (E)-form, irrespective of the nature of the solid state dimeric structure.
- Fletcher, Daniel A.,Gowenlock, Brian G.,Orrell, Keith G.
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p. 2201 - 2205
(2007/10/03)
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- Reduction of nitro aromatic compounds by zero-valent iron metal
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The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product. Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 x 10-2, 3.4 x 10-2, and 8.8 x 10- 3 min-1, respectively, in the presence of 33 g/L acid-washed, 18-20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ± 0.2 x 10-2 min-1 m-2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing rate (rpm), suggest that the observed reaction rates were controlled by mass transfer of the NAC to the metal surface. The decrease in reduction rate for nitrobenzene with increased concentration of dissolved carbonate and with extended exposure of the metal to a particular carbonate buffer indicate that the precipitation of siderite on the metal inhibits nitro reduction.
- Agrawal, Abinash,Tratnyek, Paul G.
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p. 153 - 160
(2007/10/03)
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- A Remarkable Synergic Effect of Polymer-anchored Bimetallic Palladium-Ruthenium Catalysts in the Selective Hydrogenation of p-Chloronitrobenzene
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A synergic effect of the polymer-anchored bimetallic palladium-ruthenium catalysts can lead to a remarkable increase in the selectivity for p-chloroaniline in the selective hydrogenation of p-chloronitrobenzene under atmospheric pressure and in the presence of a small amount of base.
- Yu, Zhengkun,Liao, Shijian,Xu, Yun,Yang, Bin,Yu, Daorong
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p. 1155 - 1156
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Anilines by Hydrogen Peroxide As Catalyzed by Methylrhenium Trioxide
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The oxidation of anilines by hydrogen peroxide in methanol is catalyzed by methylrhenium trioxide, CH3ReO3.The major product of the oxidation of aniline at room temperature is nitrosobenzene.For 4-substituted N,N-dimethylanilines, the N-oxide is the only product.The rate constants for the oxidation of 4-substituted N,N-dimethylanilines follow a linear Hammett relationship with ρ = -1.19.The rate constants for the reaction between CH3Re(O)2(O2), referred to as A, and 4-XC6H4-NMe2 are as follows: 4-Me, 24.5; 4-H, 18.4; 4-F, 12.7; 4-Br, 8.7; and 4-NO2, 1.0 L mol-1 s-1.This shows that electron-withdrawing substituents inhibit the reaction.The corresponding rate constant for the oxidation of aniline is 2.04 +/- 0.11 L mol-1 s-1, whereas it is 178 +/- 11 L mol-1 s-1 for the oxidation of N-phenylhydroxylamine to nitrosobenzene.A mechanism has been assigned on the basis of the kinetics and product yields.The data are consistent with the attack of the nucleophilic nitrogen atom on one of the peroxidic oxygen atom of A.The kinetics of the reaction of CH3ReO3 and hydrogen peroxide in methanol were also investigated.The formation of the 1:1 peroxide compound A is characterized by an equilibrium constant K1 = 261 +/- 6 L mol-1.The equilibration occurs rapidly: k1 = 1150 +/- 60 L mol-1 s-1 and k-1 = 4.4 +/- 0.4 s-1 at 25.0 deg C.The bisperoxide compound, CH3Re(O)(O2)2(H2O), B, forms more slowly.The rate constant is k2 = 308 +/- 16 L mol-1 s-1, and the equilibrium constant is K2 = 814 +/- 14 L mol-1 at 25.0 deg C in methanol.B reacts with the anilines, but much more slowly than A.
- Zhu, Zuolin,Espenson, James H.
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p. 1326 - 1332
(2007/10/02)
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- The Effect of Varying Halogen Substituent Patterns on the Cytocrome P450 Catalysed Dehalogenation of 4-Halogenated Anilines to 4-Aminophenol Metabolites
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The cytochrome P450 catalysed biotransformation of 4-halogenated anilines was studied in vitro with special emphasis on the dehalogenation to 4-aminophenol metabolites. The results demonstrated that a fluorine substituent at the C4 position was more easily eliminated from the aromatic ring than a chloro-, bromo- or iodo-substituent. HPLC analysis of in vitro biotransformation patterns revealed that the dehalogenation of the C4-position was accompanied by formation of non-halogenated 4-aminophenol, without formation of NIH-shifted metabolites. Changes in the apparent Vmax for the microsomal oxidative dehalogenation appeared to correlate with the electronegativity of the halogen substituent at C4, the fluorine substituent being the one most easily eliminated. A similar decrease in the rate of dehalogenation from a fluoro- to a chloro- to a bromo- to an iodo-substituent was observed in a system with purified reconstituted cytochrome P450 IIBl, in a tertiair butyl hydroperoxide supported microsomal cytochrome P450 system as well as in a system with microperoxidase 8. This microperoxidase 8 is a haem-based mini-enzyme without a substrate binding site, capable of catalysing cytochrome P450-like reaction chemistry. Together, these results excluded the possibility that the difference in the rate of dehalogenation with a varying C4-halogen substituent arose from a change in the contribution of cytochrome P450 enzymes involved in oxidative dehalogenation with a change in the halogen substituent. Rather, they strongly suggested that the difference was indeed due to an intrinsic electronic parameter of the various C4 halogenated anilines dependent on the type of halogen substituent. Additional in vitro experiments with polyfluorinated anilines demonstrated that elimination of the C4-fluorine substituent became more difficult upon the introduction of additional electron withdrawing fluorine substituents in the aniline-ring. 19F-NMR analysis of the metabolite patterns showed that the observed decrease in 4-aminophenol formation was accompanied by a metabolic switch to 2-aminophenols and N-hydroxyanilines, while products resulting from NIH-type mechanisms were not observed. For a C4-chloro-, bromo-, or iodo-substituted 2-fluoroaniline the Vmax for the oxidative dehalogenation was reduced by the additional electron withdrawing fluorine substituent at the C2 position in a similar way. In conclusion, the results of the present study strongly indicate that the possibilities for cytochrome P450 mediated dehalogenation of 4-halogenated anilines to 4-aminophenol metabolites are dependent on: (i) the characteristics of the halogen that has to be eliminated, the most electronegative and smallest ...
- Cnubben, Nicole H. P.,Vervoort, Jacques,Boersma, Marelle G.,Rietjens, Ivonne M. C. M.
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p. 1235 - 1248
(2007/10/03)
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- Chemistry of molybdenaoxaziridines. A study of oxo(N-phenylhydroxylamido-O,N)(pyridine-2,6-dicarboxylato) (hexamethylphosphortriamide)molybdenum(VI) and its catalytic properties
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The chemistry of molybdenaoxaziridines is investigated. Oxo(N-phenylhydroxylamido-O,N)(pyridine-2,6-dicarboxylato) (hexamethylphosphortriamide)molybdenum(VI) complexes 3 are prepared in high yields by different procedures, either by a reaction between anilines and oxoperoxo(pyridine-2,6-dicarboxylato)(hexamethylphosphortriamide)molybdenum(VI) (4) or by an oxidative addition reaction of nitrosobenzenes to oxo(pyridine-2,6dicarboxylato)(hexamethylphosphortriamide)molybdenum(IV) (6). The kinetics of the reactions of a series of para-substituted anilines and 4 are studied, and a Hammett plot showed a correlation between log(k/ko) and ap with a p value of -2.29. A mechanism for the formation of 3 is proposed. The electronic structure of 3 is investigated using extended-Hückel calculations. Based on the frontier orbitals of the system, a brief discussion of the chemical properties of 3 is presented. Complex 3 decomposes to mainly azoxybenzene and dioxo(pyridine-2,6-dicarboxylato)(hexamethylphosphortriamide)molybdenum(VI) (5). A variable-temperature study leads to an Arrhenius plot for this decomposition with a AC value of 16.1 kcal·mol-1. Based on the detected decomposition products and on the observed nitroso ligand exchange reaction, a mechanism for the decomposition of 3 is proposed. Treatment of 3 with hydrogen peroxide leads to a selective formation of nitrosobenzenes and 4. This reaction is further developed to a catalytic process for the selective oxidation of various substituted anilines to the corresponding nitrosobenzenes in high yields. The influences of different solvents and of the temperature on the yields of the oxidation are also examined. Based on the kinetic experiments, mechanisms for the stoichiometric and the catalytic oxidation reactions are suggested.
- M?ller, Eval Rud,J?rgensen, Karl Anker
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p. 11814 - 11822
(2007/10/02)
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- Catalytic Oxidation of Primary Aromatic Amines to the Corresponding Nitroso Compounds by H2O2 and (hmpa = Hexamethylphosphoric Triamide)
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1 catalyses the oxidation of primary aromatic amines to the corresponding nitroso derivatives, in the presence of H2O2 as oxidant.
- Tollari, Stefano,Cuscela, Michaela,Porta, Francesca
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p. 1510 - 1511
(2007/10/02)
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- Electrophilic intermediate in the reaction of glutathione and nitrosoarenes
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A kinetic study is reported of the reaction of glutathione (γ-L-glutamyl-L-cysteinylglycine, GSH) with nine substituted nitrosobenzenes (3,4-Me2 4-Me, 3,5-Me2, 3-Me, parent, 3-MeO, 4-Cl, 3-Cl, 3-NO2). Previous workers have shown that this reaction proceeds in parallel pathways, producing the appropriate N-arylhydroxylamine and GSSG or a sulfinanilide adduct ArNHS(O)G; a rapid equilibrium addition to form a common intermediate, a semimercaptal ArN(OH)SG, has also been observed. In the present study, equilibrium constants for the formation of this intermediate from ArNO and GSH have been measured by a kinetic method, and the kinetic behavior of the slower additional reactions of the semimercaptal have been examined in detail. For experiments carried out at constant pH and buffer concentration, the decay of ArN(OH)SG follows the rate law k2GSH[GSH] + k2(rearr). A comparison with product ratios previously reported shows that the bimolecular term with GSH represents the process forming ArNHOH and GSSG, while the unimolecular term represents the rearrangement to the sulfmanilide. The former process is found to be proportional to [OH-] for solutions near neutrality, is not buffer catalyzed, and has a ρ value of +1.4. This suggests a mechanism in which glutathione anion GS- reacts at the sulfur of the adduct displacing ArN-(OH) as a leaving group. The rearrangement reaction follows σ+ with a ρ+ value of -3.5 and has a rate law containing a pH-independent term and terms for catalysis by H+ and the acid component of the buffer. An 18O tracer study shows that the S=O oxygen in the sulfmanilide is derived from solvent, not the original N=O group. A mechanism is proposed with rate-limiting N-O cleavage, either uncatalyzed involving direct heterolysis with OH- as a leaving group or catalyzed by acids with H2O as the leaving group. The species produced is a cationic intermediate ArN+SG, a nitrenium ion stabilized by both the aryl ring and the directly attached sulfur atom. Aryl-stabilized nitrenium ions are commonly encountered in Bamberger-like rearrangements of hydroxylamine derivatives. The sulfur atom of PhN(OH)SG is shown to provide an approximately 106 rate acceleration for N-O cleavage in a comparison with the Bamberger rearrangement of PhNHOH.
- Kazanis, Sophia,McClelland, Robert A.
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p. 3052 - 3059
(2007/10/02)
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- Tetrabutylammoniumcerium(IV) nitrate: A mild oxidizing agent
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Tetrabutylammoniumcerium(IV) nitrate acts as a mild dehydrogenating agent for benzylic alcohols, dihydric phenols, hydrazobenzenes and arylhydroxylamines.It is found to be an effective reagent for oxidative coupling of thiols and also for iodination of polymethylbenzenes with tetrabutylammonium iodide.
- Muathen, H A
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p. 522 - 524
(2007/10/02)
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- Phenylazo-Substituted Triphenylmethylium Systems
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Triphenylmethanols (or their ethers) bearing phenylazo groups react with trifluoroacetic acid to give deeply colored solutions of the tritylium ions 7(+) - 9(+), (RC6H4N=NC6H4)nC(+)(C6H5)3-n (R = H, Me, Cl, NO2, MeO, H2N, Me2N), whose long wavelengths VIS absorptions and lowfield 1H-NMR signals are consistent with the existence of through-conjugated ?-electron systems.After addition of trifluoromethanesulfonic acid significant hypsochromic shifts of the VIS bands as well as additional proton deshieldings in the 1H-NMR spectrum are observed, which are in accordance with the formation of proximally azo-protonated phenylazotritylium ions 7(+)*H(+), 8(+)*2H(+), and 9(+)*3H(+), (RC6H4N=N(+)H-C6H4)nC(+)(C6H5)3-n.Fully analogous acid-strength-dependent ionisation/protonation reactions result for the overall p-substituted ions 17(+), 18(+), (RC6H4N=NC6H4)C(+)(C6H4R')2 (R,R' = Me, MeO, Me2N), as well as for the azobistritylium system 10(2+), (C6H5)2C(+)C6H4N=NC6H4C(+)(C6H5)2, and its azoxy derivative 11(2+).The linearly extended bis- and trisazo systems 19(+), 22(+), MeC6H4N=N(C6H4N=N)1,2C6H4C(+)(C6H5)2 and the (phenylazo)styryl system 20(+), MeC6H4N=NC6H4CH=CHC6H4C(+)(C6H5)2 in trifluoroacetic acid do not show any significant color changes relativ to the corresponding monofunctional parent types.In trifluoromethanesulfonic acid, however, compounds 19(+), 22(+) exhibit the usual bathochromic shifts of the longest wavelenght VIS absorption accompanying the increasing protonation of the polyazo system.In the case of the tritylium ions containing azomethine bridges, 24(+), only for the methoxy derivative 24b(+) indications for the existence of the conjugatively extended tritylium system (MeOC6H4N=CHC6H4)C(+)(C6H5)2 are found.The amide derivatives 26(+)-29(+), on the other hand, presents no clues for the existence of through-conjugated systems of the kind ArC(OH)=NC6H4C(+)Ar2 and ArN=C(OH)C6H4C(+)Ar2, respectively.
- Hellwinkel, Dieter,Fritsch, Helmut
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p. 2207 - 2226
(2007/10/02)
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