Photocatalytic hydrogenation of nitrobenzenes to anilines over noble metal-free TiO2 utilizing methylamine as a hydrogen donor

Since reduction and oxidation reactions simultaneously occur over a photocatalyst, a hole scavenger (a hydrogen source in the field of organic chemistry) is required to obtain a reduced product. The use of organic waste as the hole scavenger is environmentally favorable because the organic waste is degraded during the photocatalytic reduction. In this study, methylamine was used as the hole scavenger for photocatalytic reduction (hydrogenation) of nitrobenzenes over a titanium(IV) oxide photocatalyst. Corresponding anilines were obtained almost quantitatively at room temperature and under atmospheric pressure without the use of a precious metal and hydrogen gas. Nitrobenzenes having reducible functional groups such as chloro and acetyl groups were chemoselectively hydrogenated to corresponding anilines with the groups being preserved. Various parameters affecting the efficiency and the rate of the photocatalytic reaction are discussed on the basis of results of the physicochemical analyses.