Gold-catalyzed synthesis of aromatic azo compounds from anilines and nitroaromatics.

The selective formation of aromatic azo compounds at preparative or industrial levels requires stoichiometric amounts of environmentally unfriendly transition metals or nitrites. Here, we show that gold nanoparticles supported on titanium dioxide (TiO2) and nanoparticulated cerium dioxide (CeO2) catalyze the aerobic oxidation of aromatic anilines to aromatic azo compounds with yields above 98% under mild reaction conditions. Gold on TiO2 can also act as a reductive catalyst to access the compound directly from nitroaromatics through a two-step, one-pot reaction. The catalytic process shows promise for efficient synthesis of symmetric aromatic azo compounds, and even a range of asymmetric aromatic azo compounds.