Direct Functionalization of Aromatic Rings on Platinum-loaded Titanium Oxide Photocatalyst

Organic syntheses by using TiO2 photocatalysts have been extensively studied in view of green and sustainable chemistry. This highlight review shows our recent studies on photocatalytic direct functionalization of aromatic rings, i.e., aromatic ring hydroxylation with H2O and aromatic ring amination with aqueous NH3 on Pt-loaded TiO2 photocatalysts. Both reactions involve two key steps: one is an activation of a rather stable molecule (H2O or NH3) by a photoexcited hole on the TiO2 surface to produce its radical species, and the other is an aromatic substitution by the radical species through an addition-elimination mechanism. Interestingly, the radical species produced from H2O (surface oxygen radical or hydroxyl radical) is electrophilic while that produced from NH3 (amide radical) is electroneutral. These properties determine the regioselectivity in the functionalization of substituted benzene.