CuO and Ag2O/CuO catalyzed oxidation of aldehydes to the corresponding carboxylic acids by molecular oxygen.

Furfural was oxidized to furoic acid by molecular oxygen under catalysis by 150 nm-sized Ag(2)O/CuO (92%) or simply CuO (86.6%). When 30 nm-size catalyst was used,the main product was a furfural Diels-Alder adduct. Detailed reaction conditions and regeneration of catalysts were investigated. Under optimal conditions, a series of aromatic and aliphatic aldehydes were oxidized to the corresponding acids in good yields.