Efficient and green oxidation of 2-aminophenol catalyzed by tetra-(p-methoxyphenyl) porphyrin complexes anchored on chitosan in bicarbonate solution

Abstract

The study explored the catalytic activities of chitosan-supported tetra (p-methoxyphenyl) porphyrin complexes 1–3 in the heterogeneous activation of the aerobic oxidation dimerization of 2-aminophenol (OAP) to 2-aminophenoxazine-3-one (APX) in the presence of bicarbonate, simulating the function of phenoxazinone enzyme synthase. The oxidation reaction was followed by recording the UV–vis spectra of the reaction mixture with time at λmax 433 nm. All chitosan-supported metalloporphyrin complexes 1–3 exhibited effective catalytic activities for OAP oxidation. Under optimal conditions, the chitosan-supported Cu(II) (Tp-OCH3PP) complex displayed the highest catalytic efficiency. Various parameters influencing the catalytic activity of Cu(II) (Tp-OCH3PP)/CTS 1 were studied. The observed rate constant of OAP oxidation exhibited a direct correlation with the concentration of supported catalyst 1 and followed Michaelis–Menten kinetics, indicating saturation of catalyst sites with increasing OAP concentration. The study investigated the impact of temperature, bicarbonate concentration, dissolved oxygen, and the reaction mechanism. Oxidation reaction of OAP catalyzed by 1 in the presence of nitro blue tetrazolium (NTB) revealed no superoxide anion O2−• was formed as a reactive species during the reaction. The chitosan-supported Cu(II) (Tp-OCH3PP) complex shows high catalytic stability and no significant changes up to the fifth run.