Kinetics and Mechanism of the Reduction of Potassium Trisoxalatoferrate (III) by Gallic Acid in Aqueous Hydrochloric Acid Medium

Abstract

Some of the industrial or chemical importance of the reaction between gallic acid (GH) and potassium trisoxalatoferrate (III), (K₃[Fe(C₂O₄)₃] is that the product(s) of the redox reaction is used to extend the shelf 
life of food products, corrosion prevention and pollutant degradation. The redox kinetic and mechanistic studies of the reaction between gallic acid (GH) and potassium trisoxalatoferrate (III), (K₃[Fe(C₂O₄)₃] has 
been investigated in aqueous hydrochloric acid medium. The stoichiometry of the reaction determined by the mole ratio method was observed to be 1:1. The observed rate of oxidation showed first-order dependence 
with respect to both the complex and gallic acid concentrations. The experimental data for the redox system are consistent with the following rate law:where a = 5.7 × 10^-3 mol^-1 dm³ s^-1, b = 1.81 × 10^-2 mol^-2 dm⁶ s
^-1 at 420 nm and 29.0 ± 1.0 ºC. The rate of reaction was found to increase with increase in ionic strength and hydrogen ion concentration 
in the salt and acid concentration range used. The rate of reaction was also observed to increase with decreasing dielectric constant of the reaction medium and the addition of CH3COO-, HCOO-, Li+ and K+
catalyzed the rate of the reaction. The Michaelis-Menten plot of 1/kobs versus 1/[GH] gave a straight line with an insignificant positive intercept. The addition of acrylamide to the partially reacted mixture produced a gel in the presence of excess methanol. Based on the strength of the experimental data, a plausible mechanism involving outer sphere electron transfer pathway has been proposed for the redox reaction between gallic acid and potassium trisoxalatoferrate (III). The findings in this study would give more insights into the redox behaviors of the redox species and its application as a pharmaceutical and personal 
care product among others