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Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

100%

Puttaswamy, Jagadeesh R., Vaz N.

Open Chemistry

2005

vol. 3

issue 2

326-346

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO4 was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT]o, fractional-order in [substrate]o, and inverse fractional-order in [H+]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D2O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH3C6H4SO2NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.

Effect of Boronizing on the Oxidation Resistance of 316L Stainless Steel

88%

Khenifer M., Allaoui O., Taouti M.

Acta Physica Polonica A

2017

vol. 132

issue 3

518-520

The effect of boronizing treatment on oxidation at high temperature on 316L stainless steel was studied at 850, 900, 950, and 1000°C in air, for holding times between 0.25 and 24 h. The oxidation resistance of unboronized and boronized specimens was studied isothermally by thermogravimetric analyzer. The oxidation rate constant represented as a parabolic rate constant K_{p} was evaluated. Optical microscopy, X-ray diffraction, and the scanning electron microscopy were used for surface characterizations. The experimental results show that boronized coating increases the resistance of stainless steel 316l about twice and prevents oxygen from penetrating into the stainless steel substrate at the temperatures between 850 and 1000°C.

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1 Acta Physica Polonica A

1 Open Chemistry

1 2017

1 2005

1 Allaoui O.

1 Jagadeesh R.

1 Khenifer M.

1 Puttaswamy

1 Taouti M.

1 Vaz N.

Search results

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

Effect of Boronizing on the Oxidation Resistance of 316L Stainless Steel