Phototransformation of resorcinol induced by excitation of nitrite and nitrate ions. II: Nitrate ions

The excitation of nitrate ions in an aqueous solution of resorcinol (I) at pH = 5.5–6.5, leads to a mixture of 1,2,3‐trihydroxybenzene (II), 1,2,4‐trihydroxybenzene (III), 4‐nitrosoresorcinol (V) and 4‐nitroresorcinol (VII). A secondary formation of 2,4‐dinitrosoresorcinol (VI) was also detected.

Products II and III result from hydroxylation of I by hydroxyl radicals formed in the photolysis of NO^‐ ₃. . Product III does not accumulate in the solution.

The formations of products V and VII do not involve hydroxyl radicals but result from dark reactions of I with nitrogen oxides (NO₂ or N₂O₄) formed in the solution. Their formation is favoured in acidic medium. At pH = 3.1 they correspond to more than 50% of resorcinol transformed. In unbuffered solution the initial formation of V is lower than the formations of II and III but its formation rate increases with irradiation time.

Key Words:

• Photoreactions
• phenolic compounds
• resorcinol
• nitrate ions