Solvent Effect on the Oxidation of 1-Methylnaphthalene by Cobalt(III) Acetate

Abstract

The oxidation of 1-methylnaphthalene by cobalt(III) acetate has been carried out in acetic acid and in several mixtures of carboxylic acids in the absence of oxygen. The rate of oxidation in acetic acid increased fairly by adding a small amount of a strong acid, and the reduction rate of cobalt(III) acetate was related to pK_a, value of the acid added (Table 3). In the other acids with similar pK_a value to acetic acid, the rate of oxidation was smilar to that in acetic acid, and the kinds of products were the same as those in acetic acid. The molar ratios of 1-naphthylmethyl carboxylates formed as the main products were comparable to those of carboxylic acids in the solvent used (Table 5). These facts suggest that the acetate is produced by the reaction with acetate anion in the solvent and not with acetate ligands of cobalt (III) acetate. In acetonitrile-acetic acid mixtures, the reduction rate of cobalt (III) acetate decreased with increasing acetonitrile (Table 1), that is due to the substitution of the ligand of cobalt(III) ion into nitrile which has strong coordination ability (Fig.1).