The electrocatalysis of hydrogen sulfite oxidation by iron(II) complexes of 1,10-phenanthrolines

Electrocatalytic oxidation of HSO3- takes place efficiently with the catalysts of iron(II) complexes of 1,10-phenanthrolines, 2,2′:6′,2″-terpyridine and 2,2′-bipyridine. In aqueous solution, iron(II) tris(1,10-phenanthroline) is oxidized to iron(III) tris(1,10-phenanthroline) by direct electrochemical oxidation. Iron(III) tris(1,10-phenanthroline) then immediately oxidizes HSO3- to yield SO42- and S2O62- products with a rate constant of ∼105-106 M-1-1. In pH = 4.0 aqueous solution the chemical reaction of iron(III) tris(1,10-phenanthroline) with hydrogen sulfite is faster than both the hydrolysis reaction of iron(III) tris( 1,10-phenanthroline) and the reaction of hydrogen sulfite with the binuclear ion of the iron (III) phenanthroline complex. The oxidized and the hydrolyzed product of the catalyst can be reduced and returned completely to iron(II) tris(1,10-phenanthroline).