KINETICS OF REDUCTION OF HEXACYANOFERRATE(3) BY ASCORBIC ACID

The reduction of hexacyanoferrate(III) has been studied in an acidic medium using ascorbic acid (AH2) as the reducing agent. The reaction has been found to have first-order dependence in both AH2 and Fe(CN)63-. Acid concentrations retard the rate and the inverse order with respect to H+ is unity. The effect of addition of neutral salts like potassium chloride and potassium sulfate is positive and an increase in the dielectric constant of the medium also shows an accelerating effect on the reaction rate. The energy and entropy of activation for the reduction process have been calculated as 10.8 kcal and -39.8 cal deg-1 mol-1, respectively. A mechanism involving intermediate formation of ascorbate radical (AH•) has been proposed and the derived rate law agreed well with the experimental observations.