Kinetic and Mechanistic Study of Oxidation of Metoprolol in Basic Potassium Permanganate

The kinetics and mechanism of oxidation of metoprolol by alkaline potassium permanganate were studied spectrophotometrically under pseudo-first-order conditions. The reaction exhibited a strong dependence on substrate, oxidant, hydroxide ion concentration, temperature, solvent polarity and ionic strength. Increase in metoprolol, permanganate and hydroxide ion concentrations enhanced the rate of oxidation, confirming the involvement of these species in the reaction mechanism. The temperature dependence of the reaction obeyed Arrhenius equation and thermodynamic parameters suggested the formation of an ordered activated complex during oxidation. Solvent studies indicated that the reaction rate decreases with decreasing solvent polarity, which supports the participation of polar activated complexes and ion–dipole interactions. Salt effect studies showed that chloride and nitrate ions enhanced oxidation and iodide ions retarded the reaction. The oxidation proceeded via a complex-mediated inner-sphere electron-transfer mechanism involving formation of a transient manganate ester intermediate. The stoichiometric ratio of metoprolol to permanganate was found to be 1:1, and the oxidation product was identified as 1-(isopropylamino)-3-(4-(2-methoxyethyl)phenoxy)-propan-2-one. The conversion of the secondary alcoholic group of metoprolol into the corresponding ketone derivative was confirmed by FT-IR spectral analysis. In general, the study determines the kinetic behavior and mechanism of metoprolol oxidation in alkaline potassium permanganate media.