Kinetics of the Reduction of Colloidal MnO2 by Citric Acid in the Absence and Presence of Ionic and Non-ionic Surfactants

Perez-Benito and his coworkers [1] found first time quantitatively that water soluble colloidal manganese dioxide, prepared from reduction of aqueous potassium permanganate by sodium thiosulphate under neutral condition [2,3], was perfectly transparent and stable for several months. Manganese dioxide (as aqueous suspension) has been used as an oxidizing [4-7] and catalytic [8,9] agent of inorganic/organic compounds. The transparent sols of manganese dioxide too are of importance due to their involvement as active autocatalysts in many permanganate oxidations [10-12]. Surfactants are referred to as amphiphilic, amphipathic, heteropolar or polar/nonpolar compounds due to the characteristic of possessing distinct hydrophobic (water-repelling) and hydrophilic (water-loving) regions in their molecules. The interest in using surfactants as reaction media is that they affect rates, products and, in some cases, stereochemistry of the reactions [13-15]. Studies of chemical reactions in micellar media could provide understanding even about the reactions taking place at Inorganic Reaction Mechanisims, Vol. 5, pp. 151-166 © 2005 Old City Publishing, Inc. Reprints available directly from the publisher Published by license under the OCP Science imprint, Photocopying permitted by license only a member of the Old City Publishing Group.