The selectivity of the water-soluble and highly active catalyst bis(o-phenanthroline)Cu in the oxygen bleaching of pulp was explored in model compound studies. The experiments were carried out under reaction conditions typical for industrial oxygen bleaching (90 degrees C, pH 12, P(O-2) 8 bar). The generation of hydrogen peroxide was an essential step in the oxidation of the lignin model compounds, veratryl alcohol and 2,2'-biphenol. Unfortunately, bis(o-phenanthroline)Cu also catalysed the depolymerisation of the carbohydrate model compound, dextran, both with oxygen and with hydrogen peroxide. The results explain well the inadequate selectivity of bis(o-phenanthroline)Cu in the oxygen bleaching of pulp. (c) 2004 Elsevier B.V. All rights reserved.