Pd(II)-biquinoline catalyzed aerobic oxidation of alcohols in water

An aqueous palladium catalyst that is stabilized by a water-soluble biquinoline-based ligand was employed for the aerobic oxidation of secondary and primary alcohols. Secondary alcohols afforded the corresponding ketones in high yield with selectivities greater than 90%. Aliphatic primary alcohols were fully oxidized to carboxylic acid products under the same reaction conditions, with various amounts of ester byproduct. Benzyl alcohol can be converted to a mixture of benzaldehyde and benzoic acid, where the relative amounts are dependent on the reaction conditions, while substituted benzylic alcohols gave primarily benzaldehyde derivatives. In contrast to related systems, the catalyst used in this study is tolerant of additional coordinating groups on the benzyl alcohol substrate. In all examples of alcohol oxidation, water is used as the only reaction solvent and air is used as the oxidant, thus these conversions could serve as environmentally benign “green” alternatives to traditional oxidation methods.