Korean Journal of Chemical Engineering, Vol.33, No.2, 697-706, February, 2016
Oxidative conversion of anilines to azobenzenes with alkaline chloramine-T
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Anilines are widely used in the manufacture of dyes, medicinals, plastics and perfumes. Anilines are readily oxidized to give products depending on reaction conditions. Conversion of anilines to azobenzene is important in organic synthesis. In the course of this research, optimum conditions for the facile oxidative conversion of anilines to azobenzenes have been established in very good yields. The kinetics of oxidation of aniline, p-methoxyaniline, p-methylaniline, p-carboxylicaniline and p-nitroaniline by chloramine-T (CAT) in NaOH medium shows identical kinetics with a first-order dependence of rate on [CAT]o, fractional-order on [Aniline]o, and an inverse-fractional order on [OH.]. Activation parameters and decomposition constants have been determined. Oxidation products were characterized by NMR spectral studies. Isokinetic temperature is 415 K indicating enthalpy as a controlling factor. The rates increased in the order: p-methoxyaniline>p-methylaniline>aniline>p-carboxylicani- line>p-nitroaniline. A Hammett linear free energy relationship is observed for the reaction with ρ=.0.52. Reaction scheme and kinetic rate law were deduced. We have developed a simple and efficient protocol for the synthesis of azobenzenes by anilines in good yields and hence we believe that this methodology will be a valuable addition to the existing methods.
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