The Primary Photochemical Process of 4-NitropyridineN-Oxide. III. Its Photochemical Behavior in an Aqueous Solution

Abstract 4-Nitropyridine N-oxide does not undergo photochemical changes in an aqueous solution. When small amounts of 2-propanol or tetrahydrofuran were added to a deaerated solution, however, the 4-nitropyridine N-oxide was found to be reduced photochemically to afford 4-hydroxylaminopyridine N-oxide. From the measurements of the quantum yields and from flash-spectroscopic experiments under various conditions, such a photoinduced reduction of 4-nitropyridine N-oxide in deaerated water was revealed to be initiated by a hydrogen-atom abstraction from a 2-propanol or tetrahydrofuran by the triplet species. The situation was quite different from the case of an alcoholic solution, in which some intermediate species originating from the excited singlet state was responsible for the photoreduction.