In the presence of carbon monoxide and hydrogen, dicobalt octacarbonyl, co2(co)8, catalyzes the selective decarboxylation of phthalic acid or anhydride and substituted phthalic acids or anhydrides to yield the corresponding benzoic acids. In the case of pyromellitic acid, the co2(co)8 is consumed in the decarboxylation, becoming a reactant instead of a catalyst. By using derivatives of co2(co)8, in which one or two carbonyl groups are replaced by trialkylphosphine ligands, it is possible to preserve the catalytic activity of the complex. Such a catalyst will selectively decarboxylate benzenepolycarboxylic acids containing carboxyl groups as adjacent carbons to mixtures of isophthalic and terephthalic acids. By applying this reaction to a mixture of acids obtained by alkaline oxidation of coal, char, or other coal derivatives, it is possible to obtain a product rich in isophthalic and terephthalic acids.
I&ec Prod. Res. and Development, V. 9, No. 3, September 1970, PP. 347-350