Aqueous Photooxidation of ۱,۵-Dihydroxynaphthalene to Juglone Under Heterogeneous Conditions

Aerobic photooxidation of ۱,۵-dihydroxynaphthalene in water and the presence of acationic porphyrin immobilized into the pores of a nanostructured mesoporous polymer is reported.Phenolic compounds are considered as the main organic water pollutants with strong toxiceffects even at very low concentrations.[۱] Photooxidation of ۱,۵-dihydroxynaphthalene (DHN) asa representative compound of polyphenols series in the presence of various photosensitizers, hasbeen the subject of extensive studies.[۲,۳] The design of new photosensitizers with highphotocatalytic activity and oxidative stability has been of great interest for many applications.[۴] Inthe present study, a meso-tetra(aryl)porphyrin with cationic meso substituents, meso-tetrakis(Nmethylpyridinium-۳-yl)porphyrin (H۲TMPyP), immobilized on a nanostructured cation exchangepolymer, amberlyst ۱۵, nanoAmb was used as a photosensitizer for short time photooxidation ofDHN to Juglone at room temperature. As an important therapeutic phytochemical, Juglone hasmany applications as in textile, food and cosmetic industries as a natural colorants [۴]. The synthesis and characterization of the nano-structured polymer, the corresponding sodium salt and the polymer supported porphyrin were explained elsewhere. [۵,۶] The photooxidation of DHN was conducted in water in the presence of ۱۰ W white LED lamp, using the photosensitizer (nanoAmbSO۳@H۲TMPyP) and DHN in a ۱:۱۰ molar ratio. The oxidation reaction was monitored by UV-vis spectrophotometry at the λmax of DHN and Juglone, ۳۰۱ nm (ε = ۷۶۶۴ M-۱ cm-۱) and ۴۲۷ nm (ε = ۳۸۱۱ M-۱ cm-۱), respectively. The oxidation was completed in ۶۰ s (Figure ۱). No catalyst degradation was observed in the short reaction time used for the oxidation of DHN.