Aerobic alcohol oxidation catalyzed by supported ruthenium hydroxides

The supported ruthenium hydroxide (Ru(OH)x) catalysts prepared with three different TiO2 supports and an Al2O3 support showed the high catalytic activity for the oxidation of alcohols with molecular oxygen. In the presence of the most active catalyst, various kinds of alcohols could be converted into the corresponding carbonyl compounds in high yields. In addition, the catalyst could be applied to the aerobic amine oxidation. The observed catalysis was truly heterogeneous and the catalyst retrieved after the reaction could be reused with keeping its high catalytic performance. A reaction mechanism involving the ruthenium alcoholate formation/hydride abstraction (β-elimination) has been proposed. The alcoholate formation and hydride abstraction are reversible reactions. The kinetic isotope effects (kH/kD = 4.9–5.3) show that the C–H bond breaking is included in the rate-determining step. The present Ru(OH)x-catalyzed aerobic alcohol oxidation was dependent on the coordination number (CN) of nearest-neighbor Ru atoms in Ru(OH)x and the suitable CN existed.