Kinetics and mechanism of oxidation of ascorbic acid by cobalt(III) complexes in micellar media

Abstract

The kinetics of oxidation of L-ascorbic acid (H₂A) by Co(bipy)₃³⁺, Co(edta)^- and Co(atda) (tmd) complexes have been studied spectrophotometrically in the presence of cationic, cetyl trimethylammonium bromide (CTAB) and anionic sodium dodecylsulphate (SDS) surfactants in weakly acidic and basic media. The rate of ascorbic acid oxidation is influenced by the ionic nature of the micelle, hydrophobicity of the coordinated ligands and the overall charge of the complex used. Ascorbic acid oxidation by Co(bipy)₃³⁺ is slowed down in the presence of SDS while rate acceleration is observed in CTAB micellar medium. CTAB micelles also lead to rate enhancement in ascorbic acid oxidation by Co(edta)^- complex. However. micellar effect is not very pronounced in the case of neutral Co(atda) (tmd) complex as oxidant. Based on kinetic results it can be inferred that the hydrophobic interactions are dominant in the case of Co(bipy)₃³⁺ and electrostatic interactions play an important role for Co(edta)^- complex.