Benzene methylation by acetic acid with platinum-loaded titanium oxide photocatalyst

Photocatalytic functionalization of aromatic rings with simple small molecules has been intensively studied by using metal-loaded titanium oxide photocatalyst. In the present study, the photocatalytic direct methylation of benzene was examined by using acetic acid as a promising methylation reagent. Over 15% yield of toluene was achieved with a platinum-loaded TiO2 photocatalyst (Pt/TiO2) under light irradiation without any extra solvent. The kinetic investigations with isotopic compounds and temperature-controlled experiments elucidated that Pt nanoparticles on the TiO2 surface have a dual role, i.e., working as an electron receiver to improve the charge separation and catalyzing a radical addition-elimination process to form toluene molecule. Two competitive reaction mechanisms were proposed in this reaction system. [Display omitted] •Direct methylation of benzene by acetic acid was realized by TiO2 photocatalyst.•Pt cocatalyst loaded on TiO2 surface can drastically improve the product yield.•Two reaction routes, radical coupling and radical addition, were confirmed.•Two roles of Pt cocatalyst, an electron receiver and a catalyst, were revealed.