Iron-Manganese Redox Processes and Synergism in the Mechanism for Manganese-Catalyzed Autoxidation of Hydrogen Sulfite.

The mechanism for manganese-catalyzed aqueous autoxidation of hydrogen sulfite at pH 2.4 has been revised on the basis of previous comprehensive kinetic studies and thermodynamic data for iron-manganese redox processes and manganese(II) and -(III) protolysis equilibria. The catalytically active manganese species is concluded to be an oxo- (or hydroxo-) bridged mixed-valence complex of composition (OH)Mn(III)OMn(II)(aq) with a formation constant beta' of (3 +/- 1) x 10(4) M(-)(1) from kinetics or ca.