Kinetics and Mechanism of Fading of Victoria Blue Dye in Alkaline Medium

Abstract

The kinetics of fading of Victoria Blue (VB) in sodium hydroxide was studied spectrophotometrically via pseudo-first order kinetics at 616nm with the view to ascertaining the rate of reaction and possibly to propose a plausible mechanism for the reaction . The reaction showed first order dependence with respect to [VB] and also first order to  [OH-]. Michaelis-Menten plot suggested the presence of an intermediate complex. The presence of +1 and -1 charges on the reactant ions at the rate determining step was shown by the ionic strength dependence. The activation energy (Ea), ΔH‡, ΔS‡  , ΔG‡  were 52.32 kJmol-1, 50.14 kJmol-1, -0.13 kJK-1mol-1, 88.88 kJmol-1 respectively. Stoichiometric result indicated that one mole of Victoria blue dye consumed one mole of the hydroxyl ion in solution. Product analysis revealed carbinol as the major reaction product. A plausible mechanism in consonance with the kinetic and spectroscopic data was proposed. Keywords: Victoria Blue(VB), Sodium hydroxide, Potassium nitrate, Absorbance(A) Fading, Kinetics and Mechanism