Polymeric cobalt(II)-phthalocyanine exhibited much higher specific catalytic activity in sulfide ion oxidation than the monomeric counterpart. Cobalt disproportionation, 2Co 2 + Co 1 + + Co 3 + , was observed with the polymeric phthalocyanine in alkali medium. A concerted process of the oxidation and reduction steps over Co 1 + and Co 3 + active sites in the polymer gives rise to favourable conditions for an interstep energy compensation, thus lowering the activation energy of the reaction.