Oxidation of aromatic compounds by hydrogen peroxide catalyzed by mononuclear iron(III) complexes

- Iron(III) complexes were studied as catalysts in aromatic hydrocarbons oxidation.
- Toluene was oxidized in yields up to 30%, forming cresols as major products.
- The reactivity against hydrogen peroxide was followed by UV-vis and ESI-MS.
- Iron-hydroperoxide intermediate was proposed as the active catalytic species.
- o-cresol and p-cresol interacts with the intermediate forming a yellow chromophore.

In the present work, four mononuclear iron(III) complexes containing BMPA (BMPA = bis-(2-pyridylmethyl)amine) and derivative ligands, have been studied as catalyst in toluene oxidation, at 25 °C and 50 °C, using hydrogen peroxide as oxidant and acetonitrile as solvent. All catalysts were able to oxidize toluene with satisfactory yields, producing o-, m-, p-cresols, benzaldehyde and benzyl alcohol, as main products, and traces of 2-methylbenzoquinone and benzoic acid. The catalyst [Fe(BMPA)Cl3] presented the most promising results, reaching yields up to 30.2% at 50 °C after 24 h. Furthermore, [Fe(BMPA)Cl3] was applied in the oxidation of other aromatic compounds as benzene, ethylbenzene, cumene, n-propylbenzene, p-xylene and anisole. The reaction with H2O2 was monitored by electronic UV-vis spectroscopy in the presence and absence of toluene and its oxidation products, as well as by ESI-(+)-MS/Q-TOF mass spectrometry, in order to provide some information about the reaction mechanism.

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