MICELLAR EFFECTS ON THE IONIC-REDOX REACTION BRO3- BR- IN ACID-MEDIUM/

The redox reaction between bromate and bromide ions in aqueous acid me dium was studied in the absence and presence of cationic and anionic s urfactants. The rate equation in water was found to be v = k(3)(w)[BrO 3-][Br-][H+](2). The cationic surfactant, tetradecyltrimethylammonium bromide, catalyzes the reaction, using either HBr or HNO3 as the sourc e of H+; nevertheless, the observed rate constant decreases slightly, goes through a minimum, and increases again as the tetradecyltrimethyl ammonium nitrate concentration increases. The anionic surfactant, sodi um dodecyl sulfate, strongly inhibits the reaction when its concentrat ion is increased, reaching a leveling off at high surfactant concentra tion; but hydrogen dodecyl sulfate catalyzes the reaction. These micel lar effects are quantitatively explained on the basis of the pseudopha se ion exchange model: tetradecyltrimethylammonium bromide increases t he Br concentration, while sodium dodecyl sulfate decreases the H+ con centration (through the exchange with Na+ counterions) in the water ph ase where the reaction takes place.