Electrochemical study of binuclear manganese complexes as catalysts in Kraft pulp bleaching

Abstract

The redox behaviour, stability and catalytic properties of various binuclear manganese–ligand complexes was examined by electrochemical thin layer and potential measurements. Some of the complexes studied were irreversibly degraded by oxidation at high potentials, while others were dissociated in aqueous media to give the monomeric form. Otherwise, most of these complexes occur in acid–base equilibria, namely through protonation of the ligand amino functions. The manganese–Tris-(2-methyl pyridyl) amine complex is stable without dissociation at pH 3–5 and temperatures of 15–80°C. The results show that after several successive scans in the 0–1 V range the complex can be oxidised or reduced without irreversible degradation; it can be used in catalytic amounts (0.1 g of complex per g Kraft pulp) for lignin oxidation by hydrogen peroxide.