Reaction Mechanism of Aromatic Ring Hydroxylation by Water over Platinum-Loaded Titanium Oxide Photocatalyst

• Published in: Journal of physical chemistry. C Vol. 116; no. 48; pp. 25376 - 25387
• Main Authors: Yuzawa, Hayato, Aoki, Masanori, Otake, Kazuko, Hattori, Tadashi, Itoh, Hideaki, Yoshida, Hisao
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 06.12.2012
• Subjects: Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Isotope effect; Hydroxylation; Platinum; Photocatalysis; Benzene derivatives; Reaction mechanism; Ultraviolet visible spectrum; pH effect; Transition metal; Yield; Titanium oxide; Absorption spectrum
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp308453d

Direct aromatic ring hydroxylation of benzene derivatives by using water as an oxidant over platinum-loaded titanium oxide photocatalyst proceeded with high selectivity under the light of selected wavelength. Two kinds of electrophilic active species, which depended on the reaction condition, were proposed: a surface oxygen radical in neutral or acidic conditions and a hydroxyl radical in basic condition, both of which were produced by a photoformed hole on the surface of titanium oxide. In both cases, these active species can attack the aromatic ring to form an intermediate, followed by the formation of a hydroxylated product. Thus, the reaction proceeds through the addition–elimination mechanism. On the other hand, a photoformed electron reduces a proton to form a hydrogen radical, which reacts with the intermediate to produce a hydroxylated product and a molecular hydrogen or with another hydrogen radical to form a molecular hydrogen.