Autooxidation of catechols in solutions of copper(II) surfactants and hydrated metal ions in sodium dodecyl sulphate

The rates of the autooxidation of catechols in [Cu(R-tmed)X₂] (where R-tmed = N,N,N′-trimethyl-N′-alkylethylenediamine) and [Cu(R-tmed) (acac)X] micelle solutions and in transition metal ions in the presence of sodium dodecyl sulphate (SDS) were studied at 25°C in the acidic pH region. The surface-active [Cu(R-tmed)X₂] complex was found to be the most potent catalyst, with the catalytic activity increasing with the increase in the chain length of the alkyl group and with the change in the anion from chloride to bromide. The dramatic salt effect on the observed rate constants shows how an increase in the degree of micellization of the copper(II) complex with a concomitant decrease in the inter-head group distance would increase the rate of oxidation of catechol by molecular oxygen. SDS enhances the rate of copper(II) ion-catalyzed autooxidation but inhibits the manganese (II), nickel(II) and cobalt(II) ion-catalyzed reactions. The implication of the observation is discussed.