Competing processes in the photochemistry of picolines and their N-methyl salts: photoinduced charge transfer, phototransposition and photohydration

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• 作者：Vesna Blažek Bregović ; Nikola Basarić
• 关键词：Pyridine ; Pyridinium salt ; Excited state proton transfer ; Excited state charge transfer ; Phototransposition ; Photohydration
• 刊名：Research on Chemical Intermediates
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：43
• 期：2
• 页码：859-871
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Catalysis; Physical Chemistry; Inorganic Chemistry;
• 出版者：Springer Netherlands
• ISSN：1568-5675
• 卷排序：43

文摘

Photochemical reactivity of a series of picolines and their N-methylated salts has been investigated by preparative irradiations and UV–vis spectroscopy. Understanding competing photochemical processes and knowledge of their relative efficiencies is important in the application of pyridines as photocages or in the synthesis of complex polycycles. Contrary to previous reports for the gas phase, picolines are not reactive in the phototransposition, presumably due to protonation of the pyridine nitrogen in the excited state. Deuterium exchange was observed upon irradiation in CD₃CN–D₂O, but it was rationalized by photoionization and radical formation. On the other hand, N-methylated picoline salts are not protonated upon excitation. They undergo photohydration and phototransposition (Φ_R = 0.01–0.06). Upon irradiation of iodides, azabicyclic [3.1.0] hydration products were obtained. A difference in product distribution was observed between iodides and perchlorates, due to photoelimination of perchloric acid leading to the thermal aziridine ring opening. Moreover, excitation of iodide derivatives gives rise to change transfer transition forming iodide radicals that eventually give I₃− with the quantum efficiency Φ_R = 0.015–0.02.