- Electrochemically initiated transformation of 4-nitrophenylhydroxylamine into 4,4′-dinitroazobenzene
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Based on controlled potential electrolysis and cyclic voltammetry, the chain reaction of 4,4′-dinitroazobenzene formation was shown to be initiated during the electrochemical reduction of 4-nitrophenylhydroxylamine in DMF.
- Syroeshkin, Mikhail A.,Mikhalchenko, Ludmila V.,Leonova, Marina Yu.,Mendkovich, Andrei S.,Rusakov, Alexander I.,Gul'Tyai, Vadim P.
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- Kinetics and Mechanism of Oxidation of 2,4-Dinitrophenylhydrazine, p-Nitrophenylhydrazine, and p-Tolylhydrazine with Potassium Hexacyanoferrate(III) in Acidic Perchlorate Media
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The kinetics of oxidation of 2,4-dinitrophenylhydrazine (dnph), p-nitrophenylhydrazine (pnph), and p-tolylhydrazine (pth) with hexacyanoferrate(III) have been studied in acidic perchlorate solutions.The oxidation of pnph has no dependence on +> in the range 0.15-2.0 mol dm-3.In the oxidation of dnph complex formation with 3- occurs, and the reaction is independent of +> in the range 0.025-2.5 mol dm-3.The oxidation of pth in the range 0.01-1.6 mol dm-3 has been found to obey the rate low -d3->/dt = 33->1''/K1''+>) + k2'' + k3''K2''+>>, where K1'' and K2'' are the first and second protonation constants of pth, and k1'', k2'', and k3'' are the second-order rate constants for the unprotonated, monoprotonated, and diprotonated species respectively.The oxidations occur via aryldiazene and diazonium ion intermediates, to produce substituted azobenzenes and anilines as final products.In the oxidations 2-3 mol of 3- are consumed by each mol of arylhydrazine, depending on the conditions; under specific conditions, the stoicheiometry is exact.
- Gupta, Ashok K.,Gupta, Bharati,Gupta, Abhay K.,Gupta, Yugul K.
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- Correlation studies in the oxidation of Vanillin Schiff bases by acid bromate - A kinetic and semi-empirical approach
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Kinetics and mechanistic aspects of oxidation of Vanillin Schiff bases (obtained from Vanillin and p-substituted anilines) by bromate in acid medium has been studied at 313 ?K. The reaction exhibited first order in [bromate] and less than unity order each in [Vanillin Schiff base] and [acid]. The increase in the rate of reaction with decrease in dielectric constant of the medium is observed with all the studied substrates. The reaction failed to induce the polymerization of acrylonitrile. Electron withdrawing substituents in the aniline ring moiety of Vanillin Schiff base accelerate the rate of oxidation to a large extent and electron releasing substituents retard the rate. The order of reactivity is found to be p-nitro ?> ?p-bromo ?> ?p-chloro ?> ?–H ?> ?p-fluoro ?> ?p-methyl ?> ?p-methoxy ?> ?p-ethoxy and the sensitivity of the substrates towards the reaction rate is further supported by the semi-empirical calculation of electronic properties and global descriptors of the substrates (Vanillin Schiff bases) with different substituents in the aniline ring moiety. The observed trend in the reactivity of the substrates was correlated with the calculated descriptors like electronegativity, chemical potential, electrophilicity index, chemical hardness and frontier molecular orbitals. The linear free-energy relationship is characterized by a straight line in the Hammett's plot of log k versus σ. The ρ values are positive and increase with increase in temperature. From the Exner and Arrhenius plots, the isokinetic relationship is discussed. Oxidation products identified are p-substituted azobenzene and vanillic acid. Based on the experimental observations, a plausible mechanism is proposed and rate law is derived.
- Sathish,Teja, P. Ravi,Ramudu, M. Parusha,Manjari, P. Sunitha,Rao, R. Koteshwar
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- Azo synthesis meets molecular iodine catalysis
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A metal-free synthetic protocol for azo compound formation by the direct oxidation of hydrazine HN-NH bonds to azo group functionality catalyzed by molecular iodine is disclosed. The strengths of this reactivity include rapid reaction times, low catalyst loadings, use of ambient dioxygen as a stoichiometric oxidant, and ease of experimental set-up and azo product isolation. Mechanistic studies and density functional theory computations offering insight into this reactivity, as well as the events leading to azo group formation are presented. Collectively, this study expands the potential of main-group element iodine as an inexpensive catalyst, while delivering a useful transformation for forming azo compounds.
- Rowshanpour, Rozhin,Dudding, Travis
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p. 7251 - 7256
(2021/02/26)
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- Metal-Organic Capsules with NADH Mimics as Switchable Selectivity Regulators for Photocatalytic Transfer Hydrogenation
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Switchable selective hydrogenation among the groups in multifunctional compounds is challenging because selective hydrogenation is of great interest in the synthesis of fine chemicals and pharmaceuticals as a result of the importance of key intermediates. Herein, we report a new approach to highly selectively (>99%) reducing C=X (X = O, N) over the thermodynamically more favorable nitro groups locating the substrate in a metal-organic capsule containing NADH active sites. Within the capsule, the NADH active sites reduce the double bonds via a typical 2e- hydride transfer hydrogenation, and the formed excited-state NAD+ mimics oxidize the reductant via two consecutive 1e- processes to regenerate the NADH active sites under illumination. Outside the capsule, nitro groups are highly selectively reduced through a typical 1e- hydrogenation. By combining photoinduced 1e- transfer regeneration outside the cage, both 1e- and 2e- hydrogenation can be switched controllably by varying the concentrations of the substrates and the redox potential of electron donors. This promising alternative approach, which could proceed under mild reaction conditions and use easy-to-handle hydrogen donors with enhanced high selectivity toward different groups, is based on the localization and differentiation of the 2e- and 1e- hydrogenation pathways inside and outside the capsules, provides a deep comprehension of photocatalytic microscopic reaction processes, and will allow the design and optimization of catalysts. We demonstrate the advantage of this method over typical hydrogenation that involves specific activation via well-modified catalytic sites and present results on the high, well-controlled, and switchable selectivity for the hydrogenation of a variety of substituted and bifunctional aldehydes, ketones, and imines.
- Wei, Jianwei,Zhao, Liang,He, Cheng,Zheng, Sijia,Reek, Joost N. H.,Duan, Chunying
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supporting information
p. 12707 - 12716
(2019/09/04)
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- Conversion of anilines into azobenzenes in acetic acid with perborate and Mo(VI): correlation of reactivities
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Azobenzenes are extensively used to dye textiles and leather and by tuning the substituent in the ring, vivid colours are obtained. Here, we report preparation of a large number of azobenzenes in good yield from commercially available anilines using sodium perborate (SPB) and catalytic amount of Na2MoO4 under mild conditions. Glacial acetic acid is the solvent of choice and the aniline to azobenzene conversion is zero, first and first orders with respect to SPB, Na2MoO4 and aniline, respectively. Based on the kinetic orders, UV–visible spectra and cyclic voltammograms, the conversion mechanism has been suggested. The reaction rates of about 50 anilines at 20–50?°C and their energy and entropy of activation conform to the isokinetic or Exner relationship and compensation effect, respectively. However, the reaction rates, deduced by the so far adopted method, fail to comply with the Hammett correlation. The specific reaction rates of molecular anilines, obtained through a modified calculation, conform to the Hammett relationship. Thus, this work presents a convenient inexpensive non-hazardous method of preparation of a larger number of azobenzenes, and shows the requirement of modification in obtaining the true reaction rates of anilines in acetic acid and the validity of Hammett relationship in the conversion process, indicating operation of a common mechanism.
- Karunakaran,Venkataramanan
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p. 375 - 385
(2019/02/14)
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- Rh(III)-catalyzed [4?+?1]-annulation of azobenzenes with α- carbonyl sulfoxonium ylides toward 3-acyl-(2H)-indazoles
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A Rh(III)-catalyzed [4 + 1]-annulation of azobenzenes with α- carbonyl sulfoxonium ylides was developed to access 2H-indazoles in moderate to excellent yields with good functional group compatibilities. It proceeded with the sequential insertion of the Rh(III) carbene to the C?H bond and cyclization steps, where sulfoxonium ylides served as efficient and stable carbene precursor.
- Zhu, Jiawei,Sun, Song,Cheng, Jiang
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supporting information
p. 2284 - 2287
(2018/05/23)
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- When Do Strongly Coupled Diradicals Show Strongly Coupled Reactivity? Thermodynamics and Kinetics of Hydrogen Atom Transfer Reactions of Palladium and Platinum Bis(iminosemiquinone) Complexes
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The 2,2′-biphenylene-bridged bis(iminosemiquinone) complexes (tBuClip)M [tBuClipH4 = 4,4′-di-tert-butyl-N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2′-diaminobiphenyl; M = Pd, Pt] can be reduced to the bis(aminophenoxide) complexes (tBuClipH2)M by reaction with hydrazobenzene (M = Pd) or by catalytic hydrogenation (M = Pt). The palladium complex with one aminophenoxide ligand and one iminosemiquinone ligand, (tBuClipH)Pd, is generated by comproportionation of (tBuClip)Pd with (tBuClipH2)Pd in a process that is both slow (0.06 M-1 s-1 in toluene at 23 °C) and only modestly favorable (Kcom = 1.9 in CDCl3), indicating that both N-H bonds have essentially the same bond strength. The mono(iminoquinone) complex (tBuClipH)Pt has not been observed, indicating that the platinum analogue shows no tendency to comproportionate (Kcom tBuClipH2)Pt to (tBuClip)Pd occurring with ?G° = ?8.9 kcal mol-1. The palladium complex (tBuClipH2)Pd reacts with nitroxyl radicals in two observable steps, with the first hydrogen transfer taking place slightly faster than the second. In the platinum analogue, the first hydrogen transfer is much slower than the second, presumably because the N-H bond in the monoradical complex (tBuClipH)Pt is unusually weak. Using driving force-rate correlations, it is estimated that this bond has a BDFE of 55.1 kcal mol-1, which is 7.1 kcal mol-1 weaker than that of the first N-H bond in (tBuClipH2)Pt. The two radical centers in the platinum, but not the palladium, complex thus act in concert with each other and display a strong thermodynamic bias toward two-electron reactivity. The greater thermodynamic and kinetic coupling in the platinum complex is attributed to the stronger metal-ligand ? interactions in this compound.
- Conner, Kyle M.,Arostegui, AnnaMaria C.,Swanson, Daniel D.,Brown, Seth N.
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p. 9696 - 9707
(2018/08/28)
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- Visible-light-driven Efficient Photocatalytic Reduction of Organic Azides to Amines over CdS Sheet–rGO Nanocomposite
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CdS sheet–rGO nanocomposite as a heterogeneous photocatalyst enables visible-light-induced photocatalytic reduction of aromatic, heteroaromatic, aliphatic and sulfonyl azides to the corresponding amines using hydrazine hydrate as a reductant. The reaction shows excellent conversion and chemoselectivity towards the formation of the amine without self-photoactivated azo compounds. In the adopted strategy, CdS not only accelerates the formation of nitrene through photoactivation of azide but also enhances the decomposition of azide to a certain extent, which entirely suppressed formation of the azo compound. The developed CdS sheet-rGO nanocomposite catalyst is very active, providing excellent results under irradiation with a 40 W simple household CFL lamp.
- Singha, Krishnadipti,Mondal, Aniruddha,Ghosh, Subhash Chandra,Panda, Asit Baran
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supporting information
p. 255 - 260
(2018/01/15)
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- Aromatic amine oxidation process for preparing aromatic azobenzene method
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The invention relates to a method for preparing an aromatic azo compound by utilizing aromatic amine oxidation. In the method, air or oxygen serves as an oxygen source, and under the effect of a catalyst, aromatic amine is oxidized into the aromatic azo compound. The method is high in oxidization efficiency and product yield; the air or the oxygen serves as the oxygen source, and the method is economical and environmentally friendly. The product and the catalyst can be separated easily, and the aftertreatment is simple. The catalyst is easy to reuse, and the method has very good application prospect.
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Paragraph 0013; 0017
(2017/10/11)
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- First use of p-tert-butylcalix[4]arene-tetra-O-acetate as a nanoreactor having tunable selectivity towards cross azo-compounds by trapping silver ions
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p-tert-Butylcalix[4]arene-tetra-O-acetate was established for the first time as a member of the nanoreactor series, even without having any -OH group. The nano range distribution of this nanoreactor was ascertained by DLS, SEM and TEM studies. The capability of this cavitand towards hosting amines in a competitive manner generates a new green pathway for cross coupling of aromatic amines to give the corresponding azo-compounds. In this context, using p-tert-butylcalix[4]arene-tetra-O-acetate as a nanoreactor and silver nitrate as a catalyst, we got the cross azo-compound in good to excellent yields in the eco-friendly solvent water. This green methodology is also applicable for the synthesis of respective homo-compounds.
- Sarkar, Piyali,Mukhopadhyay, Chhanda
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supporting information
p. 442 - 451
(2016/01/30)
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- Method for synthesizing aromatic azo compounds
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The invention disclose a method for synthesizing aromatic azo compounds and especially relates to a method for synthesizing aromatic azo compounds by catalyzing oxidation of aromatic aniline compounds to carry out coupled dehydrogenations by themselves by adopting a manganese oxide compound synthesized by potassium permanganate and manganese nitrate in an alkaline solution as the catalyst. The method can be used to conveniently synthesize symmetrical and dissymmetrical azo compounds; reaction conditions of the method are mild, the air is utilized as an oxygen source, and no additive is added therein; thus, the method has the characteristic of simple operation, strong universality of the catalyst system as well as high yield and selectivity.
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Paragraph 0036; 0037
(2016/11/17)
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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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p. 4066 - 4069
(2016/08/18)
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- Nitric Oxide Catalysis of Diazene E / Z Isomerization
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Nitric oxide is an efficient catalyst for the cis-trans (E/Z) isomerization of diazenes. We compare the effect of room temperature solutions bearing low concentrations of nitric oxide, nitrogen dioxide, or oxygen on the rate of cis-trans isomerization, CTI, of the alkene bond in stilbene and on the azo double bond in azobenzene, as well as in four azo derivatives as measured by UV-vis spectroscopy. These rate enhancements can be as large as 3 orders of magnitude for azobenzene in solution. A mechanism is proposed where catalysis is promoted by the interaction of the nitric oxide with the diazene nitrogen lone pairs. Density functional theory, B3LYP/6-311++g suggests that the binding of NO to the diazene should be weak and reversible but that its NO adduct has an E/Z isomerization barrier of 7.5 kcal/mol.
- Bohle, D. Scott,Rosadiuk, Kristopher A.
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supporting information
p. 7145 - 7151
(2015/08/11)
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- Variable noninnocence of substituted azobis(phenylcyanamido)diruthenium complexes
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The synthetic chemistry of substituted 4,4′-azobis(phenylcyanamide) ligands was investigated, and the complexes [{Ru(tpy)(bpy)}2( μ-L)][PF6]2, where L = 2,2′:5,5′-tetramethyl-4,4′-azobis(phenylcyanamido) (Me4adpc2-), 2,2′-dimethyl-4,4′-azobis(phenylcyanamido) (Me2adpc2-), unsubstituted (adpc2-), 3,3′-dichloro-4,4′-azobis(phenylcyanamido) (Cl2adpc2-), and 2,2′:5,5′-tetrachloro-4,4′-azobis(phenylcyanamido) (Cl4adpc2-), were prepared and characterized by cyclic voltammetry and vis-near-IR (NIR) and IR spectroelectrochemistry. The room temperature electron paramagnetic resonance spectrum of [{Ru(tpy)(bpy)}2( μ-Me4adpc)]3+ showed an organic radical signal and is consistent with an oxidation-state description [RuII, Me4adpc?-, RuII]3+, while that of [{Ru(tpy)(bpy)}2( μ-Cl2adpc)]3+ at 10 K showed a low-symmetry RuIII signal, which is consistent with the description [RuIII, Cl2adpc2-, RuII]3+. IR spectroelectrochemistry data suggest that [{Ru(tpy)(bpy)}2( μ-adpc)]3+ is delocalized and [{Ru(tpy)(bpy)}2( μ-Cl2adpc)]3+ and [{Ru(tpy)(bpy)}2( μ-Cl4adpc)]3+ are valence-trapped mixed-valence systems. A NIR absorption band that is unique to all [{Ru(tpy)(bpy)}2( μ-L)]3+ complexes is observed; however, its energy and intensity vary depending on the nature of the bridging ligand and, hence, the complexes oxidation-state description.
- Choudhuri, Mohommad M. R.,Behzad, Mahdi,Al-Noaimi, Mousa,Yap, Glenn P. A.,Kaim, Wolfgang,Sarkar, Biprajit,Crutchley, Robert J.
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supporting information
p. 1508 - 1517
(2015/06/16)
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- Oxidation of aromatic anils in aniline moiety by meta-chloroperbenzoic acid in aqueous acitic medium
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The kinetics of oxidation of aromatic anils in aniline moiety by meta-chloroperbenzoic acid (m-CPBA) has been studied in aqueous acitic medium. The order of reaction was found to be second order with respect to aromatic anil and first order with respect to m-chloroperbenzoic acid. The increase of [H+] in this oxidation retards the rate of reaction. The effects of substituents on the oxidation rate were studied with 3 meta- and 5 para-substituted anils at five different temperatures. Thermodynamic parameters for the oxidation have been determined and discussed. meta-Chloroperbenzoic acid oxidation with substituted anils fulfills the isokinetic relationship and Exner relationship but not to any of the linear free energy relationships. The deviation of Hammett plot was noted and a concave downward curve was obtained for the anils with substituents in aniline moiety.
- Venkatesh,Karunakaran
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p. 2851 - 2855
(2015/12/12)
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- Schiff base complexes of rare earth metal ions: Synthesis, characterization and catalytic activity for the oxidation of aniline and substituted anilines
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Several new lanthanide complexes of Pr(III), Sm(III), Gd(III), Tb(III), Er(III) and Yb(III) with the sodium salt of the Schiff base, 2-[(5-bromo-2-hydroxy-benzylidene)-amino]-5-methyl-pentanoic acid, derived from leucine and 5-bromosalicylaldehyde have been synthesized. These complexes having general formula [Ln(HL)(NO3)2(H2O)] ·NO3 were characterized by elemental analysis, UV-vis., FT-IR, EPR, Mass spectrometry and Thermal analysis. The FT-IR spectral data suggested that the ligand behaves as a tridentate ligand with one nitrogen and two oxygen donor atoms, sequence towards central metal ion. From the analytical data, the stoichiometry of the complexes was found to be 1:1 (metal:ligand). The physico-chemical data suggested eight coordination number for Ln(III) Schiff base complexes. Thermal behaviour (TGA/DTA) and fluorescence nature of the complexes were also studied. The Gd(III) Schiff base complex was found to be an efficient catalyst for the oxidation of aniline and substituted anilines under mild conditions.
- Lekha,Kanmani Raja,Rajagopal,Easwaramoorthy
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- Oxidation of aromatic anils by sodium perborate in aqueous acetic Acid Medium
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The kinetics of oxidation of 9 meta- and 15 para- substituted aromatic anils by sodium perborate were investigated in aqueous acetic acid medium. The reaction was second order with respect to aromatic anil and first order with respect to the sodium perborate. The increase of [H+] in this oxidation retards the rate of the reaction. The observed rate constant for the substituents were plotted against the Hammett constant, δ and a non-linear concave downward curve was obtained for the anils with substituents in the aniline moiety. The observed break in the log kobs versus δwas attributed to the transition state whereas the non-linear concave upward curve was observed for the substituents in the benzaldehyde moiety and a non-linear concave upward curve was observed for the substituents in the combination of aniline and benzaldehyde moiety. The electron withdrawing substituents fall on one side of the curve, having a negative ρvalue and the electron releasing substituents fall on the other side, with a positive ρvalue and a suitable mechanism was proposed.
- Venkatesh,Karunakaran
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p. 739 - 744
(2014/06/09)
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- A practical synthesis of azobenzenes through oxidative dimerization of aromatic amines using tert-butyl hypoiodite
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A straightforward, convenient, and efficient synthetic method of azobenzenes through oxidative dimerization of aromatic amines using a unique and cost-effective iodinating reagent is described. This new method allows for easy access to both of symmetrical and unsymmetrical azobenzenes under extremely mild conditions. Georg Thieme Verlag Stuttgart. New York.
- Takeda, Youhei,Okumura, Sota,Minakata, Satoshi
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supporting information
p. 1029 - 1033
(2013/05/09)
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- Oxidative dimerization of (hetero)aromatic amines utilizing t-BuOI leading to (hetero)aromatic azo compounds: Scope and mechanistic studies
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A straightforward synthetic method of both symmetric and unsymmetric aromatic azo compounds through an efficient and cross-selective oxidative dimerization of aromatic amines using tert-butyl hypoiodite (t-BuOI) under metal-free and mild conditions has been developed. This method was also found applicable to the synthesis of heteroaromatic azo compounds. The spectroscopic study indicates the involvement of N,N-diiodoanilines in the oxidative reaction as the key intermediate.
- Okumura, Sota,Lin, Chun-Hsuan,Takeda, Youhei,Minakata, Satoshi
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p. 12090 - 12105
(2014/01/06)
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- Kinetic investigation of oxidation of aromatic anils by potassium peroxymonosulfate in aqueous acidic medium
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The kinetics of oxidation of aromatic anils to benzaldehyde and azobenzene by potassium peroxymonosulfate has been studied in aqueous acetic acid medium. The low dielectric constant of the medium facilitates the reactivity. It has been found that the variation in the ionic strength of the reaction has a negligible effect on the rate. Similarly, polymerization was not observed when acrylonitrile was added to the reaction mixture. This observation rules out the formation of any free radical in the reaction. The added Mn(II) increases the rate of the reaction, which indicates the involvement of two-electron transfer. Highly negative ΔS# values indicate a structured transition state. The deviation of the Hammett plot was noted, and a concave downward curve was obtained for the anils with substituents in the aniline moiety. The observed break in the log kobs versus σ is attributed to the transition state whereas the concave upward curve was observed for the substituents in the benzaldehyde moiety and in the combination of aniline and benzaldehyde moieties, and a suitable mechanism was proposed.
- Venkatesh,Karunakaran
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p. 542 - 550
(2013/07/26)
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- 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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- Oxidative dimerization of aromatic amines using tBuOI: Entry to unsymmetric aromatic azo compounds
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It's all the hype: An oxidative dimerization reaction of aromatic amines utilizing tert-butyl hypoiodite (tBuOI) under mild reaction conditions leads to aromatic azo compounds (see scheme). The method allows access to unsymmetric aromatic azo compounds, which are difficult to prepare by conventional synthetic methods, in a selective manner. Copyright
- Takeda, Youhei,Okumura, Sota,Minakata, Satoshi
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supporting information; experimental part
p. 7804 - 7808
(2012/09/05)
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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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- 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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- 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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- Concise preparation of azenes by oxidation of aromatic amines with molecular oxygen in subcritical water
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Reaction of organic substrates with molecular oxygen, the most abundant and accessible oxidant, has always been an attractive method for preparation of target molecules. In terms of green chemistry, non-metal-catalyzed oxidation of organic substrates is very attractive. This paper describes a general procedure for synthesis of azenes by oxidation of primary aromatic amines with molecular oxygen (3O2) in subcritical water. The reactions afforded the corresponding azenes in moderate to good yield. Springer-Verlag 2010.
- Kus, Nermin Simsek
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experimental part
p. 1089 - 1091
(2012/06/18)
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- Oxidation of anilines with hydrogen peroxide and selenium dioxide as catalyst
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A variety of substituted anilines are selectively oxidized to afford high yields of azoxyarenes by using 30% hydrogen peroxide and selenium dioxide as catalyst in methanol at room temperature. The oxidation of 4-alkoxyanilines under the same reaction conditions furnishes the corresponding 4-alkoxy-N-(4-nitrophenyl)anilines in reasonable yields, alongside other oxidation byproducts. The structure of 4-methoxy-N-(4-nitrophenyl)aniline is elucidated by X-ray crystal structure analysis. From these results, some general aspects of the reaction pathways of aniline oxidation are discussed.
- Gebhardt, Christin,Priewisch, Beate,Irran, Elisabeth,Rueck-Braun, Karola
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scheme or table
p. 1889 - 1894
(2009/04/04)
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- Reaction of aromatic nitroso compounds with chemical models of 'thiamine active aldehyde'
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Aromatic nitroso compounds in the presence of base and 2-(α-hydroxyalkyl)-3,4-dimethylthiazolium trifluoromethanesulfonate and related salts furnish in variable yields O- and N-acyl-aryl hydroxylamines and 3,4-dimethylthiazolium trifluoromethanesulfonate. A primary kinetic isotope effect of 4.9, obtained for the appropriate 2α-deuterated thiazolium salt, points to the C2α-H bond cleavage as the rate determining step. Radical species detected by ESR were unambiguously identified as phenylhydronitroxide, but attempted trapping of the corresponding C-heterocyclic radicals by TEMPO was not successful, and substrates incorporating a potential cyclopropyl radical clock gave products with the cyclopropyl ring intact. Theoretical calculations revealed a large activation energy for such reaction, which thus cannot per se exclude the intervention of such radical species. Evidence for the likely operation of two concurrent mechanisms, a radical and a preponderant ionic pathway, involving the conjugate base of the thiazolium salt, as the chemical model for 'active thiamine', and ArNO is presented for the formation of the products of the reaction.
- Ferreira, Luísa M.,Marques, M. Manuel B.,Glória, Paulo M.C.,Chaves, Humberto T.,Franco, Jo?o-Pedro P.,Mourato, Isabel,Antunes, José-Rafael T.,Rzepa, Henry S.,Lobo, Ana M.,Prabhakar, Sundaresan
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p. 7759 - 7770
(2008/12/21)
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- Preferential solvation effect on the kinetics of oxidation of para-substituted anilines by tetramethylammonium fluorochromate
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Tetramethylammonium fluorochromate (TMAFC) oxidation of para-substituted anilines, in varying mole fractions of benzene in 2-methylpropan-2-ol, in the presence of p-toluenesulfonic acid (PTS) is first-order in TMAFC and PTS and is zero-order with respect to substrate. The TMAFC oxidation of six para-substituted anilines at 298-308 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species-anilines reaction correlates with Brown-Okamoto's substituent constants affording negative reaction constant. The correlation of rate data with macroscopic solvent parameters such as εr and ET N is satisfactory while correlation with Kamlet-Taft's solvatochromic parameters (α, β, π*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity.
- Karthikeyan,Ghammami,Bhuvaneshwari,Elango
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p. 359 - 364
(2008/03/11)
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- Correlation analysis of reactivity in the oxidation of anilines by nicotinium dichromate in nonaqueous media
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The kinetics of oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate (NDC) in different organic solvent media in the presence of p-toluenesulfonic acid (TsOH) has been investigated. The rate of the reaction is zero order with respect to substrate, first order in NDC, and is found to increase with increase in [TsOH]. The various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species-anilines reaction (k2) correlates with Hammett's substituent constants affording negative reaction constants. The effect of paraand meta-substituents on the oxidation rates confirms to Swain et al.'s substituent constants F and R. both with negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as εr, and E TN while showing satisfactory correlation with Kamlet-Taft's solvatochromic parameters (α. β. and π*).
- Bhuvaneshwari,Elango
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p. 657 - 665
(2008/02/10)
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- Reaction of (4-nitorophenyl)nitrene with molecular oxygen in low-temperature matrices: First IR detection and photochemistry of aryl nitroso oxide
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The thermal reaction of (4-nitrophenyl)nitrene with oxygen in low-temperature matrices produced a new molecular species, which was identified as 4-nitrophenylnitroso oxide on the basis of its IR spectrum in combination with isotopic labeling with 18
- Inui, Hiroshi,Irisawa, Masatoshi,Oishi, Shigero
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p. 478 - 479
(2007/10/03)
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- Effect of preferential solvation on the kinetics and thermodynamics of oxidation of anilines by nicotinium dichromate
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The nicotinium dichromate (NDC) oxidation of anilines, in varying mole fractions of benzene/2-methylpropan-2-ol mixtures, in the presence of p-toluenesulfonic acid (TsOH) is first order in NDC and TsOH and zero order with respect to anilines in the concentration range investigated. The NDC oxidation of 15 meta- and para-substituted anilines complies with the isokinetic relationship but not to any of the linear free energy relationships. The activation free energy data failed to correlate with macroscopic solvent parameters such as εΓ and ENT. Correlation of ΔG# with Kamlet-Taft solvatochromic parameters (α, β, π*) suggests that the specific solute-solvent-solvent interactions play a major role in governing the reactivity.
- Bhuvaneshwari, Durvas S.,Elango, Kuppanagounder P.
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p. 1105 - 1111
(2008/02/05)
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- Novel route to azobenzenes via Pd-catalyzed coupling reactions of aryl hydrazides with aryl halides, followed by direct oxidations
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(Matrix presented) N-Boc aryl hydrazines undergo Pd-catalyzed coupling reactions with aryl halides to provide N-Boc diaryl hydrazines in excellent yields. The resulting N-Boc diaryl hydrazines were directly oxidized with NBS/pyridine in CH2Cls
- Lim, Young-Kwan,Lee, Kang-Sang,Cho, Cheon-Gyu
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p. 979 - 982
(2007/10/03)
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- Amination of benzylic C-H bonds by arylazides catalyzed by CoII-porphyrin complexes: A synthetic and mechanistic study
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CoII-porphyrin complexes catalyze the reaction of aromatic azides (ArN3) with hydrocarbons that contain a benzylic group (ArR1R2CH) to give the corresponding amines (ArR1R2C-HAr). When at least one of the R substituents is hydrogen, the catalytic reaction proceeds further to give the imine ArRC=NAr in good yields. The reaction mechanism has been investigated. The reaction proceeds through a reversible coordination of the arylazide to the ConII-porphyrin complex. This unstable adduct can either react with the hydrocarbon in the rate-determining step or decompose by a unimolecular mechanism to afford a putative nitrene complex, which reacts with more azide, but not with the hydrocarbon, to afford the byproduct diaryldiazene. The kinetics of the catalytic reaction have been investigated for a range of azides and substituted toluenes. Arvlazides with electron-withdrawing substituents react at a faster rate and a good correlation is found between the log(k) and the Taft parameters. On the other hand, an excellent correlation between the logarithm of the rate for substituted toluenes relative to that of toluene and a radical parameter (σJJ) alone was found, with no significant contribution by polar parameters. An explanation has been proposed for this anomalous effect and for the very high isotopic effect (kH/kD= 14) found.
- Ragaini, Fabio,Penoni, Andrea,Gallo, Emma,Tollari, Stefano,Li Gotti, Claudia,Lapadula, Marta,Mangioni, Enrica,Cenini, Sergio
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p. 249 - 259
(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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- Heterogeneous permanganate oxidations. A novel method for the deamination using solid supported iron-permanganate
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The heterogeneous use of potassium permanganate supported on ferrous(II)sulphate heptahydrate, provides a simple, efficient and selective means for oxidising aromatic amines to azo and aliphatic amines to carbonyl compounds.
- Barman, Dhiren C.,Saikia, Pramod,Prajapati, Dipak,Sandhu, Jagir S.
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p. 3407 - 3412
(2007/10/03)
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- Mechanism and reactivity in perborate oxidation of anilines in acetic acid
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Perborate but not percarbonate in acetic acid generates peracetic acid on standing and the peracetic acid oxidation of anilines is fast. The oxidation with a fresh solution of perborate in acetic acid is smooth and second order but the specific oxidation rate increases with increasing [perborate]0 or [boric acid]. Perborate on dissolution affords hydrogen peroxide and a borate; the latter assists the former in the oxidation. The oxidation rates of anilines under identical conditions do not conform to any of the linear free energy relationships but the reaction rates of molecular anilines do. Perborate oxidation proceeds via two reaction paths but the overall oxidation rates of molecular anilines conform to structure reactivity relationships; the transition states do not differ significantly. Analysis of the oxidation rates of perborate and percarbonate reveals that while perborate oxidation is faster than percarbonate it is at least as selective as the latter.
- Karunakaran, Chockalingam,Kamalam, Ramasamy
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p. 2011 - 2018
(2007/10/03)
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- Structure-reactivity correlation of anilines in acetic acid
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The oxidation of aniline in glacial acetic acid with percarbonate, a dry carrier of hydrogen peroxide, is a second-order reaction conforming to the isokinetic relationship. The hitherto followed method of correlation of the reaction rates in terms of the structure-reactivity relationships is unsatisfactory and erroneous. But the reaction rates of molecular anilines, obtained for the first time, conform to the structure-reactivity relationships.
- Karunakaran, Chockalingam,Kamalam, Ramasamy
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p. 1118 - 1124
(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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- Cooxidation of Anilides and Oxalic Acid by Chromic Acid: A One-Step, Three-Electron Oxidation
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The chromic acid oxidation of a mixture of oxalic acid and anilides proceeds much faster than that of either of the two substrates alone. The oxidation kinetics of acetanilide, p-methyl-, p-chloro-, and p-nitroacetanilides by Cr(VI) in the presence of oxalic acid in aqueous acetic acid medium follows first-order zero-order, and second-order dependence in [oxidant], [substrate], and in [oxalic acid], respectively, while the oxidation kinetics of benzanilide, p-methyl-, p-chloro-, and p-nitrobenzanilides follow first order in [oxidant] and fractional order each in [substrate] and [oxalic acid] and yields corresponding azobenzenes and benzaldehydes in the case of benzanilide and substituted benzanilides as the main products of oxidation. Aluminium ions suppress the reaction The intermediate is believed to be formed from the anilide and a chromic acid-oxalic acid complex In the proposed mechanism, the rate-limiting step involves the direct reduction of Cr(VI) to Cr(III).
- Ahamed, K. A. Basheer
-
-
- 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)
-
- Amination of benzylic C-H bonds by aryl azides catalysed by Co(II)(porphyrin) complexes. A new reaction leading to secondary amines and imines
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Co(II)(porphyrin) complexes catalyse the reaction of aromatic azides, ArN3, with hydrocarbons containing a benzylic group, R1R2R3CH, to give the corresponding amines, R1R2R3C-NHAr. When at least one of the R1-R3 substituents is hydrogen, the catalytic reaction proceeds further to give the imines R1R2C=NAr in good yields.
- Cenini,Gallo,Penoni,Ragaini,Tollari
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p. 2265 - 2266
(2007/10/03)
-
- Bis(1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane) peroxodisulfate: A mild and efficient oxidant for oxidation of thiols, sulfides and aromatic amines to the corresponding disulfides, sulfoxides and azo compounds
-
Bis(1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane) peroxodisulfate (BAABCPS) 1, readily prepared as orange solid from commercially available 1,4-diazabicyclo[2.2.2]octane (DABCO) and potassium peroxodisulfate converts thiols, sulfoxides and aromatic amines to the corresponding disulfides, sulfoxides and azo compounds respectively.
- Hajipour,Mohammadpoor Baltork,Kianfar
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p. 607 - 610
(2007/10/03)
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- Lack of linear free energy relationship: Tungsten(VI) catalyzed perborate oxidation of anilines
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Operation of linear free energy relationships in tungsten(VI) catalyzed perborate oxidation was studied with 29 para-, meta- and ortho-substituted anilines. The activation parameters were calculated from k*( = rate/[substrate]2) at 35, 40, 45, 50 and 55 °C using the Erying relationship by the method of least squares. The oxidation is not isoentropic; in an isoentropic series only enthalpy of activation determines the reactivity and the isokinetic temperature is at infinity. At the isokinetic temperature all the compounds of the reaction series react at equal rate, the variation of substituent at this temperature has no influence on the free energy of activation.
- Karunakaran,Palanisamy
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p. 571 - 575
(2007/10/03)
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- Interactive free energy relationship for multiple substituent effects in the oxidative cleavage of aromatic anils by N-chlorobenzamide in aqueous methanol medium
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The kinetics of the oxidation of about forty, two aromatic anils prepared from (i) unsubstituted benzaldehyde and unsubstituted aniline (ii) substituted benzaldehydes and unsubstituted aniline (iii)unsubstituted benzaldehyde and substituted anilines and (iv) substituted benzaldehydes and substituted anilines by N-chlorobenzamide in aqueous methanol medium is enhanced by electron-releasing substituents both in benzaldehydes as well as in aniline moieties while electron withdrawing substituents retarded the rate. For the series with various substituents in the ring-X (benzaldehyde) and with hydrogen in the ring-Y (aniline), the p value is -0.40. For the series with various substituents in the ring-Y and with hydrogen in the ring- X, the ρ value is -2.65. Linear plots are obtained between p(x(y)) (obtained from Hammett's plot for various substituents in the benzaldehyde moiety) and ρ(y) (substituent constants for substituents in aniline moiety) with a slope of -1.46 and between p(y(x)) (obtained from Hammett's plot for various substituents in the aniline moiety) and o (substituent constants for substituents in benzaldehyde moiety) with a slope of -1.51. This relationship has been analysed quantitatively in terms of interactive free energy relationship for multiple substituent effects.
- Mohamed Kassim,Basheer Ahamed
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p. 533 - 540
(2007/10/03)
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- Dimerization of Anilines and Benzylamines with Mercury(II) Oxide-Iodine Reagent
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By treatment with mercury(II) oxide-iodine reagent in dichloromethane at room temperature, substituted anilines were transformed to the corresponding azobenzenes. A similar treatment of benzylamines and benzhydrylamine gave N-benzylidenebenzylamines and N-benzhydrylidene-benzhydrylamine, respectively. α-Alkyl-substituted benzylamines gave diazenes and the corresponding phenyl ketones, competitively. An azine was obtained by interaction with the reagent of a benzylamine carrying an electron-withdrawing substituent at the α position, such as ethyl phenylglycinate.
- Orito, Kazuhiko,Hatakeyama, Takahiro,Takeo, Mitsuhiro,Uchiito, Shiho,Tokuda, Masao,Suginome, Hiroshi
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p. 8403 - 8410
(2007/10/03)
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- Chemical Consequences of Arylnitrenes in the Crystalline Environment
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UV photolysis of powdered crystals of several aryl azides at cryogenic temperatures afforded azo compounds predominantly. In the cases of p-(N-methylacetamido)phenyl azide and 2-azidobiphenyl, a CH insertion product or a carbazole was formed, competing with azo formation. These products can be considered to be formed through topotactic processes when the crystal structures are taken into account. The arylnitrenes generated in the azide crystals were monitored by ESR spectroscopy; they turned out to have extremely long half life-times, compared with those in the gas phase or in solution. Such high kinetic stabilities are ascribed to the inert environment around the generated nitrenes. The decay process of arylnitrenes in the initial stage obeyed a pseudo-first order kinetics; activation parameters were evaluated by Arrhenius plots. The activation enthalpies and entropies indicate that the diffusional processes of arylnitrenes may be the vital factors determining the kinetic stability and the product distribution in the crystalline environment.
- Sasaki, Akito,Mahe, Loic,Izuoka, Akira,Sugawara, Tadashi
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p. 1259 - 1275
(2007/10/03)
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- Benzyltriphenylphosphonium Peroxodisulfate (PhCH2PPh3)2S2O8: A Mild and Inexpensive Reagent for Efficient Oxidation of Organic Compounds under Nonaqueous and Aprotic Conditions
-
Benzyltriphenylphosphonium peroxodisulfate is an easily prepared and stable reagent. It could be used as an oxidant under aprotic and nonaqueous conditions in organic solvents. This reagent oxidizes different classes of alcohols to carbonyl compounds, thiols to disulfides, sulfides to sulfoxides, oximes to carbonyl compounds and aromatic amines to azo compounds efficiently. α-Hydroxy carboxylic acids and phenylacetic acids undergo oxidative decarboxylation to produce carbonyl compounds.
- Mohammadpoor-Baltork, Iraj,Hajipour, Abdol Reza,Mohammadi, Hasan
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p. 1649 - 1653
(2007/10/03)
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- An easy and efficient method for oxidation of alcohols and aromatic amines to the corresponding carbonyl and azo compounds under non-aqueous and neutral conditions
-
1-Benzyl-1-aza-4-azoniabicyclooctane periodate 1, readily prepared as an orange solid from commercially available 1,4-diazobicyclooctane, is useful for oxidation in anhydrous conditions.The reagent converts alcohols to die corresponding carbonyl compounds, α hydroxy ketones to diketones, and aromatic amines to azo compounds, in me excellent yields.The reagent ineffective in oxidising double bonds, aldehydes and ketones.
- Hajipour, A. R.,Mahboobkhah, N.
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p. 285 - 287
(2007/10/03)
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- Efficient Catalytic Oxidation of Primary Aromatic Amines to Azo Derivatives by Manganese(III) Tetraphenylporphyrin
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The oxidation of primary aromatic amines to the corresponding azo derivatives has been observed in catalytic systems containing manganese(III) tetraphenylporphyrin and sodium periodate in the presence of heterocyclic nitrogen bases acting as axial ligands.
- Habibi, Mohammad Hossein,Tangestaninejad, Shahram,Mirkhani, Valiollah
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p. 648 - 649
(2007/10/03)
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