Catalytic and induced reactions. Part II.—Catalytic and induced oxidation in the presence of salts of iron

The reactions comprised under this heading include many example of physiological importance and others well known to chemists—e. g. , the separation of iodine from potassium iodide in the presence of ferrous salts and hydrogen peroxide, first discovered by Schönbein, the process being known consequently as “Schönbein’s reaction”; and the oxidation of certain organic compounds in the presence of Fenton’s reagent (ferrous sulphate and hydrogen peroxide). Explanations of the observed phenomena have usually been based upon the hypothesis of an intermediate compound of iron; they have remained some-what tentative, however, since direct evidence of the formation of such compounds has not been forthcoming. Manchot, who investigated Schönbein’s reaction in a quantitative manner (1), came to the conclusion that hydrogen peroxide acted upon ferrous sulphate in neutral solution forming the perxide Fe2 O5 , since one equivalent of ferrous iron liberates two equivalents of iodine from potassium iodide, the latter being present in excess; allowing for the equivalent of oxygen necessary to transform ferrous iron into ferric, we obtain the total of three equivalents, or a formula of Fe2 O5 for the intermediate compound. He reached a similar conclusion from the study of the action of chromic and permanganic acids upon ferrous sulphate in the presence of acceptors; he was nevertheless quite unsuccessful in any attempt to isolate the postulated peroxides, nor have subsequent investigators fared better. Manchot decided, however, that their formation must be supposed in order to explain his results; and some such hypothesis would appear to be necessary in order to account for the reactions investigated by Fenton and others (2).