- 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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- Nitrate promoted mild and versatile Pd-catalysed C(sp2)-H oxidation with carboxylic acids
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A nitrate-promoted Pd-catalysed mild cross-dehydrogenative C(sp2)-H bond oxidation of oximes or azobenzenes with diverse carboxylic acids has been developed. In contrast to the previous catalytic systems, this protocol features mild conditions (close to room temperature for most cases) and a broad substrate scope (up to 64 examples), thus constituting a versatile method to directly prepare diverse O-aryl esters. Moreover, the superiority of the nitrate additive in this mild transformation was further determined by experimental and computational evidence.
- Hao, Hong-Yan,He, Yu-Ting,Lou, Shao-Jie,Luo, Gen,Mao, Yang-Jie,Xiong, Xue,Xu, Dan-Qian,Xu, Zhen-Yuan
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supporting information
p. 6732 - 6737
(2020/09/21)
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- Modulating the catalytic behavior of non-noble metal nanoparticles by inter-particle interaction for chemoselective hydrogenation of nitroarenes into corresponding azoxy or azo compounds
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Aromatic azoxy compounds have wide applications and they can be prepared by stoichiometric or catalytic reactions with H2O2 or N2H4 starting from anilines or nitroarenes. In this work, we will present the direct chemoselective hydrogenation of nitroarenes with H2 to give aromatic azoxy compounds under base-free mild conditions, with a bifunctional catalytic system formed by Ni nanoparticles covered by a few layers of carbon (Ni@C NPs) and CeO2 nanoparticles. The catalytic performance of Ni@C-CeO2 catalyst surpasses the state-of-art Au/CeO2 catalyst for the direct production of azoxybenzene from nitrobenzene. By means of kinetic and spectroscopic results, a bifunctional mechanism is proposed in which, the hydrogenation of nitrobenzene can be stopped at the formation of azoxybenzene with >95% conversion and >93% selectivity, or can be further driven to the formation of azobenzene with >85% selectivity. By making a bifunctional catalyst with a non-noble metal, one can achieve chemoselective hydrogenation of nitroarenes not only to anilines, but also to corresponding azoxy and azo compounds.
- Liu, Lichen,Concepción, Patricia,Corma, Avelino
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p. 312 - 323
(2018/12/11)
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- Visible-light triggered selective reduction of nitroarenes to azo compounds catalysed by Ag@organic molecular cages
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Herein, a new Ag nanoparticle (Ag NP) loaded organic molecular cage is reported. The obtained Ag@1 can act as a highly efficient heterogeneous catalyst for the selective reduction of nitroarenes to azo compounds under visible-light irradiation.
- Chen, Gong-Jun,Xin, Wen-Ling,Wang, Jing-Si,Cheng, Jun-Yan,Dong, Yu-Bin
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supporting information
p. 3586 - 3589
(2019/03/26)
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- Transition Metal-Free Oxidative Coupling of Primary Amines in Polyethylene Glycol at Room Temperature: Synthesis of Imines, Azobenzenes, Benzothiazoles, and Disulfides
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A transition metal-free protocol has been developed for the oxidative coupling of primary amines to imines and azobenzenes, thiols to disulfides, and 2-aminothiophenols to benzothiazoles, offering excellent yields. The advantageous features of the present environmentally benign methodology include the usage of biocompatible and green reaction conditions such as, solvent, room temperature reactions and transition metal-free approach. Moreover, it offers a broader substrate scope.
- Hudwekar, Abhinandan D.,Verma, Praveen K.,Kour, Jaspreet,Balgotra, Shilpi,Sawant, Sanghapal D.
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p. 1242 - 1250
(2019/01/09)
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- Super electron donor-mediated reductive transformation of nitrobenzenes: A novel strategy to synthesize azobenzenes and phenazines
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The transformation of nitrobenzenes into azobenzenes by pyridine-derived super electron donor 2 is described. This method provides an efficient synthesis of azobenzenes because of not requiring the use of expensive transition-metals, toxic or flammable reagents, or harsh conditions. Moreover, when using 2-fluoronitrobenzenes as substrates, phenazines were found to be obtained. The process affords a novel synthesis of phenazines.
- Nozawa-Kumada, Kanako,Abe, Erina,Ito, Shungo,Shigeno, Masanori,Kondo, Yoshinori
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supporting information
p. 3095 - 3098
(2018/05/22)
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- Synthesis of Azobenzenes Using N-Chlorosuccinimide and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)
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A convenient method for the synthesis of symmetrical azobenzenes is reported. This one-step procedure involves treatment of anilines with N-chlorosuccinimide (NCS) and organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). A wide range of commercially available substituted anilines readily participate in this reaction to produce the corresponding azobenzenes in moderate-to-excellent yields in minutes.
- Antoine John, Alford,Lin, Qing
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p. 9873 - 9876
(2017/09/23)
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- Kinetics and thermodynamics of oxidation of some meta-substituted anilines by tetrabutylammonium bromochromate in aqueous acetic acid medium
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The tetrabutylammonium bromochromate (TBABC) oxidation of anilines, in an aqueous acetic acid medium in the presence of perchloric acid is described. The reaction is first order with respect to aniline, TBABC and acid. The reaction rate has been determined at different temperatures and activation parameters calculated. The TBABC oxidation of meta-substituted anilines obeys Hammett relationships.
- Jabir, Shaik,Asghar, Basim H.,Mansoor, S. Sheik
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p. 288 - 295
(2017/03/17)
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- Electrocatalytic Z → E Isomerization of Azobenzenes
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A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo) switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z → E) by the same wavelength of light, which normally triggers E → Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
- Goulet-Hanssens, Alexis,Utecht, Manuel,Mutruc, Dragos,Titov, Evgenii,Schwarz, Jutta,Grubert, Lutz,Bléger, David,Saalfrank, Peter,Hecht, Stefan
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supporting information
p. 335 - 341
(2017/05/16)
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- Synchronous double C-N bond formation via C-H activation for a novel synthetic route to phenazine
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A novel synthetic strategy for phenazine formation is reported following self-coupling of anilines by Pd-Ag binary nanocluster-catalysed synchronous double C-N bond formation via non-radical mode of ortho-aryl C-H activation.
- Seth, Kapileswar,Raha Roy, Sudipta,Chakraborti, Asit K.
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supporting information
p. 922 - 925
(2016/01/16)
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- The palladium and copper contrast: A twist to products of different chemotypes and altered mechanistic pathways
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A novel contrast in palladium and copper catalysis is revealed to form products of different chemotypes resulting in a phenazine to azoarene twist through an altered mechanistic pathway (from non-radical C-H activation mode of C-N coupling to radical N-N coupling) during the oxidative self-coupling of anilines catalysed by Pd-Ag and Cu-Ag nanoclusters.
- Seth, Kapileswar,Roy, Sudipta Raha,Kumar, Asim,Chakraborti, Asit K.
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p. 2892 - 2896
(2016/05/24)
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- Palladium-Catalyzed Oxidative Synthesis of Unsymmetrical Azophenols
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A straightforward palladium-catalyzed oxidative hydroxylation of azobenzenes is reported. The developed methodology tolerates various functional groups and allows the synthesis of diverse unsymmetrical azophenols under mild conditions in good to excellent yields. A complementary procedure was also investigated by in situ generation of PIFA. This study represents the first general method for the synthesis of o-hydroxyazobenzenes starting from simple azoarenes.
- Nguyen, Thi Hong Long,Gigant, Nicolas,Delarue-Cochin, Sandrine,Joseph, Delphine
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p. 1850 - 1857
(2016/03/15)
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- Rhenium-Catalyzed [4 + 1] Annulation of Azobenzenes and Aldehydes via Isolable Cyclic Rhenium(I) Complexes
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The first Re-catalyzed [4 + 1] annulation of azobenzenes with aldehydes was developed to furnish 2H-indazoles via isolable and characterized cyclic ReI-complexes. For the first time, the acetate-acceleration effect is showcased in Re-catalyzed C-H activation reactions. Remarkably, mechanistic studies revealed an irreversible aldehyde-insertion step, which is in sharp contrast to those of previous Rh- and Co-systems. (Chemical Presented).
- Geng, Xiaoyu,Wang, Congyang
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supporting information
p. 2434 - 2437
(2015/05/27)
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- An efficient catalyst-free and chemoselective synthesis of azobenzenes from nitrobenzenes
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NaOH mediated reaction of nitrobenzenes in EtOH was performed at 80 °C temperature affording azobenzenes in excellent yield. This methodology presents an easy synthesis of a wide variety of azo compounds from readily available nitrobenzene derivatives. This journal is
- Gund, Sitaram H.,Shelkar, Radheshyam S.,Nagarkar, Jayashree M.
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p. 42947 - 42951
(2015/02/19)
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- Kinetics and mechanism of meso-tetraphenyl-porphyriniron (III) chloride catalyzed oxidation of aniline and its substituents by oxone in aqueous acetic acid medium
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Metalloporphyrins are present naturally in cytochromes and hemoglobins. Perhaps the most interesting feature of heme-enzymes, such as cytochromes P450, is their ability to perform extremely difficult oxidations with high selectivity. The present work is undertaken with the aspiration of designing the mechanistic studies on meso-tetraphenylporphyriniron(III) chloride catalyzed oxidation of anilines by potassium peroxymonosulfate (oxone) in aqueous acetic acid medium. The study of oxidation with respect to the catalyst reveals that there is degradation of the catalyst. The concentration-protonated aniline (a less reactive species) increases due to the increase in [H+], which inhibits the rate of the reaction. The thermodynamic parameters for the oxidation have been determined and discussed. It confirms the Exner relationship and also the activation parameters to the isokinetic relationships. The oxone oxidation with 12 meta- and para-substituted anilines complies with the isokinetic relationship but not with any of the linear free energy relationships. The solvent interaction plays a major role in governing the reactivity. A suitable mechanism is proposed for this reaction.
- Raja,Karunakaran
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p. 580 - 587
(2013/08/23)
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- Study of halogen-mediated weak interactions in a series of halogen-substituted azobenzenes
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The azobenzenes, known for their various importance in the industry, have been chosen as model compounds to understand the role of weak interactions involving the C-X (X = F, Cl, and Br) bond using single-crystal X-ray diffraction technique, especially in the absence of other stronger intermolecular forces such as hydrogen bonds. The fluorinated compounds have been found to pack in the lattice by utilizing C-H···F hydrogen bonds, whereas the chlorinated and brominated analogues have been found to prefer C-X···X-C, C-X···π, and π···π interactions while packing in the lattice. The stabilization energy offered by the C-H···F hydrogen bonds and the C-X···X-C interactions have been estimated by computational methods using Gaussian 09, and the topological properties have been determined by using the AIM2000 package. The lattice energy decomposition has been done using semiclassical density sums (SCDS) PIXEL method. Our studies indicate that the stabilization energy offered by each C- H···F hydrogen bond lies in the range from -0.8 to -1.0 kcal/mol, while that for the C-X···X-C interaction has been found to be -0.35 kcal/mol for the X = Cl interaction and -0.73 kcal/mol for the X = Br interaction. Further, the analysis of these interaction by atoms in molecules (AIM) theory indicates that the electron densities (ρc) at the bond critical points (BCP) for C-H···F and C-X···X-C (X = Cl and Br), calculated using the AIM2000 package, are small (-3), and the values of Laplacian (?2ρc) are positive. This indicates that these interactions are of the hydrogen bond type. A detailed study of these interactions by experimental and computational methods has been described in the manuscript.
- Karanam, Maheswararao,Choudhury, Angshuman Roy
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p. 4803 - 4814
(2013/12/04)
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- Meso-tetraphenylironporphyrin(III) chloride catalyzed oxidation of aniline and its substituents by m-chloroperbenzoic acid
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The most fascinating feature of heme-enzymes such as cytochromes P450 is their ability to carry out oxidations with high selectivity. Metalloporphyrin complexes are used as replicate compounds for cytochrome P450. A kinetic analysis has been carried out with the aim of understanding the mechanistic studies on oxidation of anilines by m-chloroperbenzoic acid catalyzed by meso-tetraphenylironporphyrin(III) chloride in aqueous acetic acid medium. The order of the reaction is found to be second order with respect to the substrate and first order with respect to the catalyst and oxidant. Product analysis proves that azobenzene is the sole product in the catalytic oxidation. The increase of [H+] in this oxidation retards the rate of the reaction. The effects of substituents on the oxidation rate are studied with 19 ortho-, meta- and para- substituted anilines at five different temperatures. The thermodynamic parameters for the oxidation have been determined and discussed. The catalysed m-chloroperbenzoic acid oxidation with substituted anilines fulfills the isokinetic relationship and Exner correlation but not to any of the linear free energy relationships. The solvent interaction also plays a major role in leading the reactivity. Based on the kinetic results and product analysis a probable mechanism is proposed.
- Raja,Karunakaran
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p. 1355 - 1360
(2013/06/27)
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- Selective N-oxidation of aromatic amines to nitroso derivatives using a molybdenum acetylide oxo-peroxo complex as catalyst
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The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO)3(C{triple bond, long}CPh); Cp = η5-C5H5 with H2O2, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.
- Biradar, Ankush V.,Kotbagi, Trupti V.,Dongare, Mohan K.,Umbarkar, Shubhangi B.
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p. 3616 - 3619
(2008/09/19)
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- Chemical oxidation of fluoroanilines to fluoroazobenzenes and fluorophenazines with potassium ferricyanide and potassium hydroxide
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The oxidation of several fluoroanilines with potassium ferricyanide and potassium hydroxide is described. In this oxidation, the major products are fluoroazobenzenes. In the case of 2-fluoro-substituted anilines, heterocyclic fluorophenazines were obtained in low to moderate yields. The optimal conditions for the reaction and the mechanism are presented.
- Leyva, Elisa,Medina, Concepcion,Moctezuma, Edgar,Leyva, Socorro
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p. 1712 - 1715
(2007/10/03)
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- Anti-androgenic activity of substituted azo- and azoxy-benzene derivatives.
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Substituted phenylazo and phenylazoxy compounds were systematically prepared and their anti-androgenic activity was measured in terms of (1) the growth-inhibiting effect on an androgen-dependent cell line, SC-3, and (2) the binding affinity to nuclear androgen receptor. Generally, azo/azoxy compounds showed cell toxicity, and the growth-inhibiting effects on SC-3 cells correlated with the toxicity. However, some compounds, including 4,4'-dinitroazobenzene (25), 4,4'-dimethoxyazobenzene (33), and 2,2'-dichloroazoxybenzene (47), possessed potent anti-androgenic activity without apparent cell toxicity.
- Takahashi,Ishioka,Koiso,Sodeoka,Hashimoto
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p. 1387 - 1390
(2007/10/03)
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- Oxidation of fluoroanilines to fluoroazobenzenes with potassium ferricyanide and KOH
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The oxidation of several fluoroanilines to fluoroazobenzenes with potassium ferricyanide and KOH in a solvent mixture of ethanol/water is described.
- Leyva, Elisa,Monreal, Elena,Medina, Concepcion,Leyva, Socorro
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p. 7847 - 7848
(2007/10/03)
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- Photochemistry of Fluorinated Aryl Azides in Toluene Solution and in Frozen Polycrystals
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Several fluorinated triplet aryl nitrenes have been generated in low-temperature polycrystals by photolysis of the corresponding azides.Upon extended photolysis at -196 deg C the nitrenes abstract hydrogen from frozen toluene to give anilino-benzyl radical pairs, which subsequently combine to give CH insertion products.The radical pairs and the triplet nitrenes have been detected by EPR.In toluene solution, the major reaction products are tar, the corresponding fluorinated anilines, and azo compounds.
- Leyva, Elisa,Munoz, Daniel,Platz, Matthew S.
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p. 5938 - 5945
(2007/10/02)
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- STUDIES ON THE MECHANISM OF THE OXIDATION OF AROMATIC PRIMARY AMINES WITH LEAD TETRAACETATE
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The oxidation of eight substituted anilines with lead tetraacetate gives azo derivatives and products deriving from nucleophilic nuclear attack.A ligand transfer mechanism and a reaction path via aminium radical is suggested for these oxidations.
- Benedini, Francesca,Galliani, Guido,Nali, Micaela,Rindone, Bruno,Tollari, Stefano
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p. 343 - 346
(2007/10/02)
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