| Abstract: | The quantum yield of the phototransformation of 4-nitrophenol has been evaluated as 4.5×10−5±0.6×10−5 at pH=2; at 3.0×10−5±0.6×10−5 at pH=5.5; 1.8×10−5±0.5×10−5 at pH=8.3. However the half-life is relatively low and no accumulation of aromatic or quinonic products was observed. Hydroquinone (QH2) is the main organic primary product formed when an air-saturated or degassed solution was irradiated in 365 nm monochromatic light (about 80% of the 4-nitrophenol initially converted at pH=5.5 in the absence of oxygen). In air-saturated neutral or acidic solution, the formation of NO−3 ions accounted for about 80% of the 4-nitrophenol converted, but in degassed medium a mixture NO : NO−2 : NO−3 is formed. An heterolytical mechanism of photohydrolysis with primary formation of QH2 and HNO2 is suggested. Several by-products as benzoquinone, 4-nitrosophenol, 4-nitrocatechol and nitrohydroquinone are formed according to the conditions. Many secondary reactions are involved as the disproportionation or the oxidation of HNO2, the oxidation of QH2 by HNO2 and oxidations induced by excitation of NO−2 and NO−3. |
