- 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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- Synthesis and characterization of azo aromatic diacyl chlorides
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A convenient and rapid method for the synthesis of azo aromatic diacyl chlorides has been developed. Eight azo aromatic diacyl chlorides have been synthesized from aromatic nitro acids by using xylene as solvent. Most reaction periods are less than 2 h and the products are obtained in excellent yields with high purity.
- Qiu, Ming Yan,Zhang, Ji Chang,Shi, Wei Yun,Jia, Qing Chao,Niu, Yong Sheng
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experimental part
p. 2295 - 2297
(2012/09/22)
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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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- 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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- 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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- 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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- 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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