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The catalytic properties of in situ formed copper(II) complexes of N,N,N′,N′-tetramethylethylenediamine (TMEDA), rac-1,2-diaminocyclohexane (DACH) and 9,10-diaminophenantrene (DAPHEN) were investigated under optimized reaction conditions in the oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) with molecular oxygen in alkaline aqueous solutions. The kinetics of the reaction, catalytic species and their deactivation were studied, in order to clarify the reasons for low conversions in Cu(TMEDA) and Cu(DACH) catalyzed reactions. The most active catalyst was the scarcely soluble Cu(DAPHEN) with turn over number 5700 in the oxidation of veratryl alcohol. The catalytic precursors in Cu(TMEDA) catalyzed reactions is binuclear hydroxyl bridged complex (LCu-μ-(OH)2-CuL)2+. The main reason for the deactivation of these catalysts according to our results is the reactivity of the ligands under reaction conditions.

Catalytic activities of 189 metal–ligand combinations in aqueous alkaline solution were studied in the oxidation of veratryl alcohol with molecular oxygen. The parallel screening revealed high oxidation activity of copper ions with dimethylglyoxime, 2,2′-bipyridine and 1,10-phenanthroline ligands. Further study with these in situ prepared catalysts indicated that ionic complexes with two ligands are probably the most active. The maximum activities of the three catalysts were achieved at different pH and metal–ligand molar ratio. In 3 h reaction with catalyst–substrate molar ratio 1:1000, the highest turnover numbers obtained were 420 for the Cu-dimethylglyoxime catalyst, 830 for Cu-bipyridine and 760 for Cu-phenanthroline. These most effective Cu-complexes catalysed not only the oxidation of lignin model compounds but also the depolymerisation of the carbohydrate model compound dextran. Results achieved in oxygen delignification of softwood pulp were in accordance with the model compound studies; the catalysts effectively lowered the kappa number, but they also tended to damage the cellulose fibres.