Iron porphyrins as biomimetical models for disperse azo dye oxidation

The commercial ironporphyrins 5,10,15,20-tetrakis-(4-carboxyphenyl)porphyrin iron(III) chloride, 5,10,15,20-tetrakis-(N-methyl-4-pyridyl)porphyrin iron(III) pentachloride and 5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)porphyrin iron(III) chloride were investigated as cytochrome P450 models for the oxidation of the azo dyes Disperse Black 3 (DB3), Disperse Orange 3 (DO3) and Methyl Yellow (MY). Iodosylbenzene, tert-butyl hydroperoxide and hydrogen peroxide were used as oxidants. The oxidation reactions were monitored by UV-Vis absorption spectroscopy, by the observation of the absorption band characteristic of each dye, followed by product identification via high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The catalytic systems were efficient for the oxidation of the dyes, leading to 4-nitroaniline and 4,4'-dinitroazobenzene; 4-methylamino-azobenzene, 4-aminoazobenzene, and 4-nitroazobenzene; and 4,4'-dinitroazobenzene as oxidation products, respectively. The oxidation products resulted from the oxidation of the terminal amine in the case of all the dyes, and the azo bond remained intact for DB3 and MY dyes. For DO3 dye, the azo bond is broken resulting in the formation of 4-nitroaniline. Similar products were observed for the oxidation of DO3 in biological systems, showing that the catalytic systems studied herein are good biomimetical models.