Photoinduced reactions of selected azo dye metabolites in water

The photochemical reactions of eight azo dye metabolites [o-aminotoluene (1 ), 4,4'-thiodianiline (2), 4,4'-diaminodiphenylmethane (3), p-chloroaniline (4), 2,4-toluylenediamine (5), p-kresidine (6), 2,4-diaminoanisole (7), an d 2-naphthylamine (8)], which are frequently detected in aquatic systems, w ere investigated in water under UV-light. Direct photolysis was investigate d at two wavelengths (> 230 and > 290 nm) and under varying partial pressur e of oxyg photolysis processes were studied by irradiation of the azo dye m etabolites in the presence of different trapping, agents to identify reacti ve oxygen species possibly participating; in the reaction. Kinetic experime nts were executed to determine quantum yields and environmental lifetimes ( ELT) of the metabolites. The stability,en directly depended on of these sub stances against oxygen directly depended on their structure, with p-chloroa niline (4) and 2,4-diaminoanisole (7) being most stable and o-aminotoluene (1) and 2-naphthylamine (8) being least stable. Photolytic half-life times varied between ca. 15 min and more than 2 h (with lambda > 230 nm) and betw een a little more than 1 h and ca. 22 h (with lambda > 290 mn). Several products could be identified by HRGC-MS. Furthermore, a new photoox idation reaction could be observed during the conversion of 2-naphthylamine (8) in the presence of oxygen. A phenazine derivative could be identified as the end product. Generally, it can be assumed that the oxidation process es are more important for the environmental conversion of azo dye metabolit es than reductive processes.