275219 Synthsis of Ionic Metalloporphyrins and Application in the Selective Oxidation of o-Nitrotoluene to o-Nitrobenzonic Acid As Catalysts
Metalloporphyrin complexes with conjugated macrocycles may be used as a model for cytochrome P-450 to selectively activate dioxygen or substrates under mild conditions. The synthesis and biomimetic catalytic applications of porphyrins have been widely investigated in recent decades. At present, the majority of synthetic metalloporphyrins is hydrophobic, whereas all of the porphyrins in the organisms of living bodies are water-soluble. Therefore, it’s significant to investigate the synthesis and applications of water-soluble metalloporphyrin compounds. The ionic water-soluble tetrapyridylporphyrin (TPyP) was bonded to quaternary bromoalkane via exterior ring pyridyl groups [tetra(N-cetyl-4-pyridyl)porphyrins bromide, TCPyP] and then coordinated with different central metal ions to prepare the ionic metalloporphyrins [tetra(N-cetyl-4-pyridyl)porphyrins metal bromide, TCPyPM, M=Fe, Mn, Co, Cu, Zn], which were used as biomimetic catalysts in the selective catalytic oxidation of o-nitrotoluene (ONT) to o-nitrobenzonic acid (ONBA).
In this work, the metalloporphyrins with water-soluble quaternary ammonium moieties were synthesized via multi-step reactions. Simultaneously, the structures of free base porphyrins and metalloporphyrins were characterized by UV-vis, IR and 1HNMR. Subsequently, the applications of above porphyrin catalysts in catalyzing oxidation of o-nitrotoluene to o-nitrobenzonic acid under mild conditions were investigated. The o-nitrobenzonic acid selectivities of 83%~89% were obtained, which were much higher than the selectivity (54% selectivity) of blank experiments. Especially, the effects of peripheral substituents and central metal ions on the product selectivities were discussed in detail. Therefore, the ionic water-soluble metalloporphyrins, introduced with quaternary ammonium moieties, can play an obvious catalytic role than the foregoing aliphatic metalloporphyrins in aqueous biomimetic catalytic reactions.
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