Kinetics of oxidation of acetylsalicylic acid (Aspirin) by manganese(III) in pyrophosphate medium

Abstract

Manganese(III) has been stabilized in weakly acidic medium by means of pyrophosphate and the nature of the complex elucidated spectrophotometrically. Stoichiometry of manganese (III) oxidation of aspirin (acetylsalicylic acid) in pyrophosphate has been established in the <i>p</i>H range 2.3-3.5 by iodometric and spectrophotometric methods. The reaction follows

first order kinetics in [Mn(III)]_o. There is a first order dependence on aspirin in the <i>p</i>H range 2.5-3.5, while other common features include positive fractional order dependence on [H⁺], inverse fractional order depends upon[Mn(II)] in the <i>p</i>H range studied. Effects of varying ionic strength, and solvent composition have been studied. Added ions such as SO₄^2- and

ClO₄^-alter the reaction rate and mechanism by changing the formal redox potential of Mn(III)-Mn (II) couple. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanism consistent with the kinetic data has been proposed and discussed.