CHARACTERIZATION OF THE REACTION OF COBALT(II) ACETATE, DIOXYGEN AND ACETIC-ACID, AND ITS SIGNIFICANCE IN AUTOXIDATION REACTIONS

When cobalt(II) acetate is added to an oxygenated solution of acetic acid at reflux, a reaction occurs producing cobalt(III) acetate, carbon dioxide, carbon monoxide, methane, methyl acetate and water. Evidence is presented that this reaction is initiated by a trace amount of adventitious peroxide in acetic acid and is then is propagated via a free radical chain reaction. A balanced set of reactions is given which are consistent with the products observed. It is suggested that this is the initiation step in cobalt-catalyzed autoxidations in acetic acid. Of the first row metal acetates from calcium to zinc, only cobalt(II) acetate undergoes this reaction. It is shown that cobalt is, by far, the most active autoxidation catalyst toward p-toluic acid in acetic acid. The author concludes that the Co(OAc)2/O2/HOAc reaction is one of the reasons for cobalt's unique character as an autoxidation catalyst in carboxylic solvents.