Cyclohexane oxidation catalyzed by mononuclear iron(III) complexes

Abstract

In this work, we present the oxidation of cyclohexane catalyzed by a family of mononuclear iron(III) complexes: [Fe(BMPA)Cl 3] 1, [Fe(MPBMPA)Cl 3] 2, [Fe(PBMPA)Cl 2] 3 and [Fe(PABMPA)Cl 2](ClO 4) 4 using hydrogen peroxide or tert-butyl hydroperoxide as oxidant, in acetonitrile solution. These complexes were able to oxidize the cyclohexane into cyclohexanol and cyclohexanone with good yields. It was also possible to characterize by gas chromatography and mass spectrometry the by-products, cyclohexyl hydroperoxide and tert-butyl cyclohexyl peroxide. Adipic acid (AA) was also formed in the reaction and it was determined by titration. The reactions with hydrogen peroxide exhibited much greater yields (about 30% for all the complexes) than when tert-butyl hydroperoxide was employed (about 17% of yield with complex 1). The alcohol/ketone ratio in the reactions with hydrogen peroxide after 24 h was around 1.5, indicating cyclohexanol selectivity, while with tert-butyl hydroperoxide the ratio was around 0.7–1.0. In conclusion, the studied complexes can be considered good catalysts to oxidize the cyclohexane in mild conditions.