ELECTROCHEMICAL REDUCTION OF NITRITE AND NITRIC-OXIDE CATALYZED BY AN IRON-ALIZARIN COMPLEXONE ADSORBED ON A GRAPHITE ELECTRODE

The ligand alizarin complexone, [((3,4-dihydroxy-2-anthraquinolyl)methyl)imino]diacetic acid is strongly and irreversibly adsorbed on graphite electrode surfaces and binds ferric ions to form surface-bound metal complexes. Upon reduction, the adsorbed complex is an active electrocatalyst for the reduction of both nitrite and nitric oxide. A rotating platinum ring-graphite disk electrode was employed to detect in situ the products of nitrite reduction. The main products of this electrocatalytic nitrite reduction are believed to be NH2OH and NH3. Adducts formed between substrate and adsorbed catalyst are formed in the initial steps of the reduction on the basis of surface cyclic voltammetric behavior. The possible application of this electrocatalytic reduction in the analysis of nitrite and nitric oxide is also discussed. Four other ligands, xylenol orange, methylthymol blue, fluorexon, and thymolphthalein complexone, which have the same coordination structure of a (methylimino)diacetate group and an adjacent aromatic hydroxyl group, were also electrocatalysts for nitrite reduction.