Photochemical and photosensitised reactions involving 1-nitronaphthalene and nitrite in aqueous solution

The excited triplet state of 1-nitronaphthalene, 1NN, ((3)1NN) is able to oxidise nitrite to ˙NO(2), with a second-order rate constant that varies from (3.56 ± 0.11) × 10(8) M(-1) s(-1) (μ±σ) at pH 2.0 to (3.36 ± 0.28) × 10(9) M(-1) s(-1) at pH 6.5. The polychromatic quantum yield of ˙NO(2) photogeneration by 1NN in neutral solution is Φ(˙NO(2))(1NN)≥ (5.7 ± 1.5) × 10(7)× [NO(2)(-)]/{(3.4 ± 0.3) × 10(9)× [NO(2)(-)] + 6.0 × 10(5)} in the wavelength interval of 300-440 nm. Irradiated 1NN is also able to produce ˙OH, with a polychromatic quantum yield Φ(˙OH)(1NN) = (3.42 ± 0.42) × 10(-4). In the presence of 1NN and NO(2)(-)/HNO(2) under irradiation, excited 1NN (probably its triplet state) would react with ˙NO(2) to yield two dinitronaphthalene isomers, 15DNN and 18DNN. The photonitration of 1NN is maximum around pH 3.5. At higher pH the formation rate of ˙NO(2) by photolysis of NO(2)(-)/HNO(2) would be lower, because the photolysis of nitrite is less efficient than that of HNO(2). At lower pH, the reaction between (3)1NN and ˙NO(2) is probably replaced by other processes (involving e.g.(3)1NN-H(+)) that do not yield the dinitronaphthalenes.