The mechanism of the ferric ferricyanide reduction reaction

Abstract

The ferric ferricyanide reaction has been generally considered to depend on the reduction of ferricyanide to ferrocyanide and, in the presence of the ferric ion, the consequent production of Prussian Blue. In testing the ability of ferricyanide to prevent the azo-coupling reactions of enterochromaffin cells and of the noradrenaline islets of the adrenal medulla, ferricyanide proved to be an effective oxidant in alkaline solution, but failed to quinonize the two catechols below pH 6. Similar results are obtained in oxidative blocking of cutaneous sulphydryl sites against the ferric ferricyanide reaction and against staining by the mercaptide acid azo-coupling reaction of Lillie & Glenner (1965). Ferric ferricyanide solutions are used at pH 2–2.5 and the ferric ion is an effective quinonizing and thiol-oxidizing agent at this pH level; the ferricyanide ion is not. The ferric ferricyanide reaction depends on the reduction of ferric to ferrous ions in the presence of ferricyanide, with the production of Turnbull's Blue.