The Oxidation of o-Xylene and o-Toluic Acid in Acetic Anhydride Catalyzed by Cobalt(II) and Bromide Ions Reactivity of o-Toluic Acid

Abstract

The oxidation of o-toluic acid was studied using cobalt (II) and bromide ions as catalyst in acetic anhydride, and the reactivity was compared with that in acetic acid. In acetic anhydride, phthalic anhydride could be prepared in one step but a large amount of 3-acetoxyphthalide was also produced (Fig.4). Acetic anhydride was hydrolyzed as the oxidation proceeded, and stoichiometry of the hydrolysis suggested that the overall oxidation formula in acetic anhydride could be expressed as follows (Eq. (1), ( 2)).
In acetic acid, phthalic acid was the mai n product and phthalic anhydride as well as phthalide was also detected in the products as intermediates to phthalic acid (Fig.5). It was observed that 86% of cobalt (II) acetate added as catalyst precipitated and the bromide ion was converted to the organic bromine when the oxidation was performed in acetic anhydride (Fig.7), but not in acetic acid (Fig.8 ). Bromoacetic acid was identified as the organic br omo compound formed in acetic anhydride. However, in the oxidation of o-xylene in acetic acid, the bromide ion was once changed to organic bromine at the initial stage of the oxidation, and then the ion was regenerated with the increasing concentration of o-toluic acid formed in the reaction system (Fig.9).