- A complete vibrational study on a potential environmental toxicant agent, the 3,3′,4,4′-tetrachloroazobenzene combining the FTIR, FTRaman, UV-Visible and NMR spectroscopies with DFT calculations
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In this study 3,3′,4,4′-tetrachloroazobenzene (TCAB) was prepared and then characterized by infrared, Raman, multidimensional nuclear magnetic resonance (NMR) and ultraviolet-visible spectroscopies. The density functional theory (DFT) together with the 6-
- Castillo, María V.,Pergomet, Jorgelina L.,Carnavale, Gustavo A.,Davies, Lilian,Zinczuk, Juan,Brandán, Silvia A.
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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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- 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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- Oxidation of dichloroanilines and related anilides catalyzed by iron(III) tetrasulfonatophthalocyanine
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We investigated the degradation of polychlorinated pollutants, such as dichloroanilines and related anilides, catalyzed by iron(III) tetrasulfonatophthalocyanine (FePcS) with potassium monopersulfate or hydrogen peroxide as oxidant. The reaction is influenced by the positions of the two chloro-substituents and by the nature of the oxidant. The FePcS- catalyzed oxidation of 3,5-dichloroaniline with potassium monopersulfate leads to the formation of more biodegradable products (carboxylic acids) and to potentially toxic dimers (azo and azoxy compounds). The oxidation of 3,4- dichloroaniline by FePcS/H2O2 converts this pollutant into coupling products. The formation of dimers in the catalytic oxidation of dichloroanilines can be avoided by acylation of the amine function.
- Hadasch, Anke,Meunier, Bernard
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p. 2319 - 2325
(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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- Towards the synthesis of aminodibenzo[b,e][1,4]dioxin derivatives via cationic ruthenium complexes
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Double nucleophilic aromatic substitution reactions between N-substituted (η6-1,2-dichlorobenzene)RuCp+ salts and substituted 1,2-benzenediols have been carried out under mild conditions to prepare N-substituted (η6-dibenzo[b,e][1,4]dioxin)ruthenium(II) complexes. The dibenzodioxin ligands were subsequently liberated by photolysis, with radiation from a sunlamp or from a medium pressure Hg lamp (300 nm).
- Cambie, Richard C.,Clark, George R.,Coombe, Sheryl L.,Coulson, Sally A.,Rutledge, Peter S.,Woodgate, Paul D.
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- Catalytic selective oxidation of amines with hydroperoxides over molecular sieves: Investigations into the reaction of alkylamines, arylamines, allylamines and benzylamines with H2O2 and TBHP over TS-1 and CrS-2 as the new catalyst
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The liquid phase oxidation of various substituted amines with dil H2O2 and tert-butyl hydroxyperoxide (TBHP) has been investigated over titanium and chromium silicates respectively. While TS-1/H2O2 combination exhibits a remarkable activity and selectivity in the oxidation of arylamines to produce the symmetrical azoxybenzenes, CrS-2 catalyzes the selective oxidation of various substituted amines to the corresponding nitro compounds by oxidation with 70% TBHP. The nature of the reactive intermediates during the oxidation of anilines to nitrobenzenes has been established using cyclic voltammetry experiments. Further, amines possessing α C-H bonds are selectively oxidized to either oximes or the carbonyl compounds on reaction with H2O2 catalyzed by TS-1.
- Suresh,Joseph,Jayachandran,Pol,Vinod,Sudalai,Sonawane,Ravindranathan
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p. 11305 - 11318
(2007/10/02)
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- DETERMINATION OF 3,3',4,4'-TETRACHLOROAZOBENZENE IN WATER BY ISOTOPE DILUTION GAS CHROMATOGRAPHY/HIGH RESOLUTION MASS SPECTROMETRY
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A methodology, based on gas chromatography/high resolution mass spectrometry selected ion monitoring (GC/HRMS SIM) has been developed for the determination of 3,3',4,4'-tetrachloro-azobenzene (TCAB), a potential carcinogen, in water. As internal standard we prepared labelled TCAB, from labelled benzene. TCAB was extracted from water by hexane followed by a cleanup column chromatography over basic alumina. Recoveries of TCAB range from 80.0-88.3 percent. The detection limit of TCAB is about 50 fg of TCAB or 5 ppq in 1,000 mL of water.
- Schneider, Serge,Hashimoto, Shunji,Yamamoto, Takashi,Morita, Masatoshi
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- Competitive Base-Induced α-Elimination and Methanolysis of N-Aryl-O-pivaloylhydroxylamines
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The N-aryl-O-pivaloylhydroxylamines 1a-c are quite stable in MeOH under neutral conditions, but under mildly basic conditions (0.05 M Et2NH or Et3N) they undergo rapid decomposition (t1/2 = ca. 3-5 h at 25 deg C) by two competitive processes: apparent α-elimination to generate the nitrenes 2a-c and pivalic acid and basic ester methanolysis to generate the hydroxylamines 3a-c and methyl pivalate.The nitrenes decompose into the corresponding anilines 5 and azobenzenes 7, while the hydroxylamines undergo nitrene-mediated oxidation into the corresponding azoxybenzenes 6.The mechanism of this latter process was probed by addition of excess hydroxylamine, and a mechanism for the oxidation consistent with available data (Scheme II) is proposed.It was also found that the nitrosobenzenes 8 undergo nucleophilic attack by conjugate bases 4a-c of the title compounds to produce one of the two possible isomeric nonsymmetrical azoxybenzenes.
- Novak, Michael,Martin, Kristy A.,Heinrich, Julie L.,Peet, Kristine M.,Mohler, Linda K.
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p. 3023 - 3028
(2007/10/02)
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- Barium Manganate Oxidation in Organic Synthesis: Part I - Oxidation of Aromatic Primary Amines
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Aromatic primary amines undergo oxidative coupling to form azo compounds in the presence of barium manganate under heterogenous conditions.
- Srivastava, Ram Gopal,Pandey, Ram Lakhan,Venkataramani, Pudukkottai S.
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p. 995 - 996
(2007/10/02)
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