Kinetics and mechanism of oxidation of 1,10-phenanthroline by alkaline permanganate

The kinetics of the oxidation of 1,10-phenanthroline (1,10-phen) by permanganate were investigated in alkaline medium. A first-order, fractional-order and zero-order dependence of the rate each in [MnO4 −], [1,10-phen] and [OH−], respectively, was observed. The data suggest that the oxidation proceeds via the formation of a complex between 1,10-phen and MnO4 − which decomposes in a slow step to yield the free radical of 1,10-phen, followed by a fast step to give 2,2′-bipyridy1 3,3′-dicarboxaldehyde. The reaction constants involved in the mechanism were evaluated. There was good agreement between the observed and calculated rate constants under varying conditions of the experiments. The activation parameters were calculated with respect to the slow step of the mechanism.