Catalytic oxidation of 4-(dimethylamino)benzaldehyde by gold nanoparticles. Part I: Reaction characterization

Absorption spectra collected for samples in aerobic and anaerobic conditions show that gold nanoparticles in an aqueous medium in the presence of dissolved oxygen catalyze the oxidation of 4-(dimethylamino)benzaldehyde to 4-(dimethylamino)benzoic acid in the pH range 2.6-11.7. GC and GC-MS results show that at acidic pH the only additional product is 4-(methylamino)benzoic acid whereas at basic pH a variety of by-products are formed. The 15 nm diameter gold particles employed are much larger than the gold particle diameters typically used for CO oxidation. An indirect mechanism in which chemisorbed atomic oxygen serves as the oxidizing agent is proposed.