Determining the TiO2-Photocatalytic Aryl-Ring-Opening Mechanism in Aqueous Solution Using Oxygen-18 Labeled O2 and H2O

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• 作者：Xibin Pang ; Wei Chang ; Chuncheng Chen ; Hongwei Ji ; Wanhong Ma ; Jincai Zhao
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：June 18, 2014
• 年：2014
• 卷：136
• 期：24
• 页码：8714-8721
• 全文大小：492K
• 年卷期：v.136,no.24(June 18, 2014)
• ISSN：1520-5126

文摘

The molecules O₂ and H₂O dominate the cleavage of aromatic sp² C鈥揅 bonds, a crucial step in the degradation of aromatic pollutants in aqueous TiO₂ photocatalysis, but their precise roles in this process have remained elusive. This can be attributed to the complex oxidative species involved and to a lack of available models for reactions with a high yield of direct products. Here, we used oxygen-18 isotope labeled O₂ and H₂O to observe the aromatic ring-opening reaction of the model compound 3,5-di-tert-butylcatechol (DTBC), which was mediated by TiO₂ photocatalysis in an aqueous acetonitrile solution. By analyzing the primary intermediate products (75% yield), especially the seven-membered ring anhydrides that were formed, we obtained direct evidence for the oxygen atom of dioxygen insertion into a C鈥揅 bond of the aromatic ring. This indicates that molecular oxygen is the ultimate ring-opening agent in TiO₂ photocatalysis and that it undergoes single O atom incorporation rather than the previously proposed molecular oxygen 1,2-addition processes. The ratio of intradiol to extradiol products depends on the particle size of TiO₂ catalysts used, which suggests that the O₂ activation is correlated with the available coordination sites on the TiO₂ surface in the photocatalytic cleavage of the aromatic ring.