hidroxilação de alcano por sistemas suportados em sílica e estudos exploratórios da oxidação do contaminante emergente triclosan

Abstract

In this work, cytochrome P450-inspired biomimetic oxidation systems were developed for aliphatic C–H bond activation and triclosan oxidation. Heterogenization of Mn(III) N-pyridylporphyrin derivatives onto silica gel resulted in three groups of catalysts. Immobilization of Mn(III) N-pyridylporphyrins (MnT-X-PyPCl, X = 2, 3, 4) on chloropropylfunctionalized silica gel (Sil-Cl) yielded the first group of catalysts, Sil-Cl/MnT-X-PyPCl. The second group was prepared by in situ methylation of Sil-Cl/MnT-X-PyPCl materials resulting in the Sil-Cl/MnT-X-PyPCl/MeOTs materials. Finally the third group of catalysts were prepared via electrostatic immobilization of Mn(III) N-methylpyridiniumporphyrins (MnTM-X-PyPCl5, X = 2, 3, 4) onto unfunctionalized silica gel to yield SiO2/MnTM-XPyPCl5 (X = 2, 3, 4). These materials were studied as catalysts for iodosylbenzene-based hydroxylation reactions of the model substrate cyclohexane. The heterogenized catalysts proved to be more efficient, selective and oxidatively stable than the corresponding homogeneous systems for cyclohexane oxidation. No significant loss in catalytic efficiency was observed upon recycling of these materials. The increase in Mn(III)/Mn(II) reduction potentials associated with the alkylation of the pyridyl moieties of Sil-Cl/MnT-XPyPCl/MeOTs (X = 2, 3, 4) materials did not result in significant changes in catalytic efficiency as compared with the non-methylated starting materials Sil-Cl/MnT-X-PyPCl (X = 2, 3, 4). The PhIO-oxidation of the emerging contaminant triclosan under homogenous conditions was carried out using Mn porphyrins as biomimetic catalysts for P450-based xenobiotic degradation. The second generation catalyst Mn(III) meso-tetrakis(2,6- dichlorophenyl)porphyrin chloride, MnTDCPPCl, was more efficient and oxidatively stable than its first generation analogue Mn(III) meso-tetraphenylporphyrin chloride, which was considerably destroyed during the reactions. GC-FID, HPLC-DAD and LC-MS/MS analyses were used to confirm the formation of two products already identified as in vivo metabolites of triclosan: 4-chlorocatechol and 2,4-dichlorophenol. LC-MS/MS spectra of reation mixture indicated the formation of four additional triclosan degradation products (m/z 270, 323, 448, and 483), whose structural identity and biological relevance have yet to be confirmed.