Oxidations by manganese VII

The kinetics of the oxidation of Fe(CN)6 - by permanganate have been examined in phosphate buffers over the pH range 1.6-6.3. The stoichiometry 

30 and = 0.0933 M, the rate coefficient k is 2.64x lO l.mole . sec . This value was verified by monitoring the rate of formation of Fe(CN)g at 420 m/i, by which method k = 2.56x 10 l.mole .sec . Increase in acid concentration increases the rate of reaction activation parameters are quoted at low and high acidities. In the range pH 5-6 the rate-controlling step may involve an ion-pair formed with (or Na ) from the buffer 

As the pH is reduced to pH 3 the rate increases, and eventually achieves a limiting value at pH 2.5. The following scheme, with protonated species, is suggested as likely at pH 1-2. 

The ratio of unreduced to reduced cobalt is variable and is dependent on the concentration of Mn04 , viz. 

By way of contrast, oxidation of the organic ligand in oxalatopentaamminecobalt-and p-aldehydobenzoatopentaamminecobalt(lll) is accompanied by reduction of the cobalt(IIl) centre in the case of one-equivalent oxidants, e.g. Ce(lV), but not in the case of two-equivalent oxidants e.g. CI2). The rate law is simple 

---