Oxidative Degradation of Methyl Green Dye by Cyanide Ion in Aqueous Perchloric Acid Medium; Kinetics, Thermodynamic and Mechanistic Approach

Abstract

The Kinetics of the redox reaction of methyl green (MG 2+) and Cyanide ion (CN-) in aqueous HClO 4 has been investigated spectrophotometrically at [H + ] = 2.0 x 10-3 mol/dm 3 , µ = 0.196 mol/dm 3 , T = 31±1 o C and λ max = 630 nm. The reaction is first order in (oxidant: reductant). With second order overall, with stoichiometry of 1:2 (Oxidant:Reductant). The observed rate constants were not affected by changes in acid concentration, but enhanced by change in ionic strength concentration. The rate constant was catalyzed mildly with varying dielectric constant of the reaction medium. Added anions have no effect the reaction while cations inhibit the reaction rate. The reaction obeys the rate law: − [ 2+ ] = k 2 [MG 2+ ][CN-] k 2 = (4.00±0.06) x 10-1 dm 3 /mol/s Evidence from Spectroscopic study suggests the absence of stable intermediate complexes at the course of the reaction. Also, the activation enthalpy (ΔH* = +24.942 kJ /K/mol) and entropy (ΔS* =-0.173 KJ/K/mol) were determined in favour of endothermic reaction. Plausible mechanism involving an outer-sphere complex has been proposed to explain the results.