The oxidation of salicylic acid and acetylsalicylic acid by water-soluble colloidal manganese oxide in surfactant and polymer media: a kinetic and mechanistic approach

Kinetics of the oxidation of both salicylic acid and acetylsalicylic acid by colloidal manganese oxide (MnO2) have been explored spectrophotometrically by monitoring the decay in the absorbance of colloidal MnO2 at 390 nm in absence and presence of surfactants and polymers. The major goal of this research is the study of the effect of the nature of surfactants and polymers on the rate of the oxidation of salicylic acid and acetylsalicylic acid, as well as employing of Piszkiewicz and Menger-Portnoy models to explain the catalytic and inhibition effect of surfactants and polymers. However, the experimental runs have been carried out under the pseudo-first-order reaction conditions with respect to MnO2. The oxidation has been observed to be fractional-order with respect to both of salicylic acid and acetylsalicylic acid, colloidal MnO2 and H2SO4. The anionic surfactant, sodium dodecyl sulfate (SDS) and the nonionic surfactant Tween-20 have been observed to be reaction inhibitors. Whereas, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) causes flocculation with oppositely charged colloidal MnO2 and therefore could not be studied further in all cases. On the other hand, PEG 600 and 1500 have played a significant role in enhancing the rates of the reaction. On the basis of observed kinetic results, a plausible mechanism of the reaction and the expected final product have been suggested.