The photoreduction of 3-benzoylpyridine: an experimental and theoretical study of the formation of the intermediate LAT

Abstract

3-Benzoylpyridine (3-BPy) triplet abstracts hydrogen from alcohols to give a ketyl radical similar in its properties to that of benzophenone. In neat isopropanol, the main product of the ketyl radical reactions is the pinacol while in water–isopropanol mixed solvent a ‘light absorbing transient’(LAT) accumulates. This is much more stable than the LAT formed by photolysis of benzophenone and results from the coupling of two 3-BPy ketyl radicals, with attack of one of them on the 6 position of the pyridine ring of the other. Chemical evolution of this intermediate leads in part to an oxidized product conserving the same skeleton. Theoretical calculations and transient absorption spectroscopy support the structure of the intermediate and the proposed mechanism of reaction.