Kinetics of the reduction of water soluble colloidal MnO2 by mandelic acid in the absence and presence of non-ionic surfactant triton X-100

Kinetics of the title reaction has been studied spectrophotometrically in presence of perchloric acid at 30A degrees C both in the absence and presence of Triton X-100 (TX-100). The reaction-time curves suggest the involvement of non-autocatalytic and autocatalytic reaction paths. The reaction follows first-order kinetics with respect to colloidal MnO2 and mandelic acid. The reaction has acid-dependent and acid-independent paths and, in the former case, the order is fractional in [H+]. Addition of nonionic surfactant (TX-100) catalysed the reaction which is explained on the basis of hydrogen bonding between the oxygen of polyoxyethylene chains of TX-100 and hydroxy groups of mandelic acid/colloidal MnO2. The kinetic data are rationalized in terms of model proposed by Tuncay et al. On the basis of the observed results, a possible mechanism has been proposed and discussed.