(768d) 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^[1] and biomimetic catalytic applications^[2] 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.

References:

[1] Sun ZC, She YB, Zhou Y, Song XF, Li K. Synthesis, characterization and spectra properties of substituted tetraphenylporphyriniron chloride complexes. Molecules. 2011; 16: 2960-2970.

[2] Kumari P, Sinha N, Chauhan P, Chauhan SMS. Isolation, synthesis and biomimetic reactions of metalloporphyrinoids in ionic liquids. Current Organic Synthesis. 2011; 8: 393-437.