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- First-row-transition ion metals(II)-EDTA functionalized magnetic nanoparticles as catalysts for solvent-free microwave-induced oxidation of alcoholsPublication . Martins, Nuno; Martins, Luisa; Amorim, Carlos O.; Amaral, Vitor; Pombeiro, ArmandoA series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA), as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs) was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4@EDTA-M2+ [M = Mn2+ (1), Fe2+ (2), Co2+ (3), Ni2+ (4), Cu2+ (5) or Zn2+ (6)] were characterized by FTIR (Fourier Transform Infrared) spectroscopy, powder XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectrometer), VSM (Vibrating Sample Magnetometer) and TGA (Thermal Gravity Analysis). The application of the magnetic NPs towards the microwave-assisted oxidation of several alcohol substrates in a solvent-free medium was evaluated. The influence of reaction parameters such as temperature, time, type of oxidant, and presence of organic radicals was investigated. This study demonstrates that these MNPs can act as efficient catalysts for the conversion of alcohols to the corresponding ketones or aldehydes with high selectivity and yields up to 99% after 2 h of reaction at 110 degrees C using t-BuOOH as oxidant. Moreover, they have the advantage of being magnetically recoverable catalysts that can be easily recycled in following runs.
- Solvent-free microwave-induced oxidation of alcohols catalyzed by ferrite magnetic nanoparticlesPublication . Martins, Nuno; Martins, Luisa; Amorim, Carlos O.; Amaral, Vitor; Pombeiro, ArmandoA series of first-row-transition-metal ferrite magnetic nanoparticles (NPs) MFe2O4 [M = Mn2+ (1), Fe2+ (2), Co-2+ (3), Ni2+ (4), Cu2+ (5) or Zn2+ (6)] were prepared by the co-precipitation method and characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscope -energy dispersive X-ray spectrometry (SEM-EDS), vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). Those NPs were used as catalysts for the microwave-assisted oxidation of various alcohols in solvent-free medium. MnFe2O4 (1), CoFe2O4 (3) and CuFe2O4 (5) act as catalysts for the conversion of alcohols to the corresponding ketones or aldehydes with a yield range of 81 to 94% in 2 h at 120 degrees C using t-BuOOH as an oxidant. These catalysts can be readily isolated by using an external magnet and no significant loss of activity is observed when reused up to 10 consecutive runs. The effects of some parameters, such as temperature, time, type of oxidant and presence of organic radicals, on the oxidation reactions were also investigated. The presented literature overview highlights the advantages of our new 1-6 NPs catalytic systems in terms of efficiency and economy, mainly due the used microwave (MW) heating mode.