A kinetic study of the reaction between colloidal manganese dioxide and formic acid in aqueous perchloric acid solution in the presence of surface active agents

The kinetics of the reaction between colloidal manganese dioxide (obtained by reduction of potassium permanganate with sodium thiosulfate) and formic acid at 25 degrees C and constant ionic strength in aqueous perchloric acid solution were studied in the presence of surface active agents, such as ca tionic cetyltrimethylammoniumbromide (CTAB), anionic sodium lauryl sulfate (SDS), non-ionic Triton X-100. The reaction rate was followed spectrophotometrically by measuring the chan ges in absorbance at 500 nm. The results were analyzed by means of the fixe d time method. Cationic surfactants cause flocculation of the oppositely charged colloidal MnO2 and could not be used, whereas anionic micellar systems were found to be ineffective on the reaction rate. No noticeable effect of SDS on the re action rate was observed, even at high concentrations. This reaction was fo und to be accelerated by non-ionic micelles of Triton X-100. The reaction w as first-order with and without surfactants, and the rate constant, k, incr eased as Triton X-100 concentration increased and reached a plateau at high er concentrations. (C) 1999 Elsevier Science B.V. All rights reserved.