How Does the C鈥揌alogen Bond Break in the Photosubstitution Reaction of 3-Fluorobenzophenone in Acidic Aqueous Solutions?

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• 作者：Jinqing Huang ; Jiani Ma ; Mingde Li ; Mingyue Liu ; Xiting Zhang ; David Lee Phillips
• 刊名：Journal of Organic Chemistry
• 出版年：2015
• 出版时间：October 2, 2015
• 年：2015
• 卷：80
• 期：19
• 页码：9425-9436
• 全文大小：902K
• ISSN：1520-6904

文摘

The efficient photosubstitution reaction of m-fluorobenzophenone and the related photohydration reactions were systematically investigated in acidic aqueous solutions. The mechanisms and intermediates were directly characterized by femtosecond transient absorption spectroscopy and nanosecond time-resolved resonance Raman spectroscopy, which is supported by density functional theory calculations. This photosubstitution was found to be a two-step process, based on the observation of a meta-hydration intermediate. The protonation of the ketone was confirmed as a crucial precursor step for further photochemical reactions as indicated by the observation of the absorption spectrum of an excited triplet protonated species. More interestingly, the efficient photosubstitution reaction could selectively occur under specific conditions. Control experiments on a series of halogen-substituted benzophenones were conducted to study the influence of the solution acidity, substituent positions, and the kind of substituted halogens on the efficiency in forming the corresponding hydroxyl photosubstitution product. Some practical conditions in predicting the efficiency of the photosubstitution reaction of interest are summarized, and they were successfully used to predict when the photosubstitution reaction takes place for some other halogen-substituted benzophenone derivatives. The driving force of this photosubstitution reaction may provide insights into several possible applications which are also briefly discussed.