Kinetic Study of the Oxidation of Formate by Iodine in Micellar Solutions of Alkyltrimethylammonium Chlorides

Article abstract of DOI:10.1246/bcsj.56.75

The spectrophotometric study was made of the oxidation of formate by iodine in micellar solutions of decyl- and dodecyltrimethylammonium chlorides.In the presence of the cationic surfactant micelles, the reaction was found to take place only at the micellar surface according to the same mechanism as in water.The experimental second-order rate constant rose steeply to a maximum at the critical micelle concentration and then decreased monotonously with increasing surfactant concentration.A tentative estimation based on a charged-phase separation model led to the true second-order rate constant in micellar phase of 0.03-0.07 mol^-1 dm³ s^-1 at 30 deg C, which is comparable with that in water.Thus the observed rate enhancement in cationic surfactant solutions can be interpreted in terms of an increase in surface concentration of the formate ion arising from an electrostatic interaction with the micellar ion.The micellar effects on the formation constant of triiodide ion are also discussed.