PHOTOCHEMISTRY AND ENVIRONMENT .14. PHOTOTRANSFORMATION OF NITROPHENOLS INDUCED BY EXCITATION OF NITRITE AND NITRATE IONS

The excitation of NO2-, HNO2 or NO3- in the presence of nitrophenol induces hydroxylations in the ortho or para positions with respect to the phenol function. No nitration is observed in contrast with phenol and hydroxybiphenyls. The reaction can be attributed to hydroxyl radicals formed in the photolysis of NO2-, HNO2 and NO3-. With nitrite, the reaction is more efficient at 253.7 nm than at longer wavelengths. This effect is not observed with HNO2. When NO2- or HNO2 are excited in the presence of nitrophenol, the formation of dihydroxynitrobenzenes competes with the scavenging of hydroxyl radicals by nitrite ions (or HNO2) and the efficiency of the reaction is significantly influenced by the relative concentrations.