Photochemistry and environment XII: Phototransformation of 3-nitrophenol in aqueous solution

The quantum yield φ of phototransformation of 3-nitrophenol is very low, but a strong wavelength effect is observed. At pH 2.2 in degassed solution φ_{254 nm} = 7.3 × 10⁻⁵ and φ_{365 nm} = 4.5 × 10⁻⁶. The effect of dissolved oxygen on the photoreactions remains limited. Seven organic photoproducts were identified: resorcinol, 4-nitrosoresorcinol, 2,4-dinitrosoresorcinol, 3-nitrocatechol, 4-nitrocatechol, nitrohydroquinone and 2,3′-dihydroxy-4-nitrobiphenyl. From the inhibiting effect of ethanol it can be concluded that resorcinol is mainly formed through a primary heterolytic photohydrolysis of 3-nitrophenol. The formation of nitrosoresorcinol and the nitrodiphenols can be attributed to the reactions of hydroxyl radicals formed by nitrite (or nitrate) ion excitation.