Photocatalytic conversion of nitroaromatic compounds in the presence of TiO2

The combination of a solid photocatalyst (TiO2) and a co-catalyst (p-toluenesulfonic acid) has been successfully applied for the light-induced conversion of five different derivatives of nitrobenzene (o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), p-nitrotoluene (p-NT), 5-nitro-m-xylene (DMNB), and p-nitrophenol (p-NPh)) in O2-free ethanolic suspensions yielding substituted quinolines and tetrahydroquinolines. GC–MS analysis of the irradiated mixtures showed the formation of substituted quinolines as the main products when DMNB, m-NT, and p-NPh were employed as substrates, while ethoxy-tetrahydroquinolines were obtained when o- and p-NT were used. DMNB has been chosen as model substrate for a more detailed study focusing on the influence of the concentration of the photocatalyst, the co-catalyst, and the nitroaromatic compound on the yield of the products. Depending on the compounds that have been detected by GC–MS the reaction mechanism is discussed.