Mechanism of the photochemical transformation of naphthalene in water

Upon irradiation in air-saturated aqueous solution, naphthalene is mainly converted into 7-hydroxy-1,4-naphthoquinone, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde. The quantum yield of photolysis is equal to 0.0025±0.0005. Naphthalene is likely to be phototransformed via monophotonic ionization that occurs with a quantum yield equal to 0.02. The radical cations formed after the electron ejection can deprotonate or react with water yielding radicals that are oxidized by molecular oxygen. Finally, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde are yielded. The production of 7-hydroxy-1,4-naphthoquinone is consistent with the intermediary formation of photolabile 1,4-naphtoquinone.