Fluoride doping in the CeO2 lattice has been achieved by a simple, reliable, reproducible, and safe solution-based method. F-containing CeO2 has retained the fluorite structure, and its effect has been confirmed from various analytical techniques such as powder X-ray diffraction, Fourier transform IR, Raman, UV-visible diffuse reflectance, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy-dispersive X-ray (EDX) and transmission electron microscopy-EDX analysis. The concentration of fluoride in the CeO2 lattice has been determined from chemical analysis and core-level XPS analysis. The concentration of Ce(3+) in the F-doped and undoped CeO2 samples have been determined both from XPS analysis as well as from variable-temperature magnetic susceptibility measurements. The characteristic Ce(3+) emission in the PL spectrum indicated the increase of Ce(3+) ion concentration in the F-doped sample, conforming to the results from XPS and magnetic measurements. F-doped CeO2 nanocrystals showed moderate monodispersity as determined from particle-size measurements using dynamic light scattering experiments and high surface area of 106.1 m(2)/g. Optical band gap of CeO2 has narrowed upon doping with fluoride ions from 3.05 to 2.95 eV. The formation of extrinsic oxygen vacancy complexes upon F-doping has been observed in the Raman spectrum (at 1097 cm(-1)) in addition to fingerprint bands of CeO2. The UV-shielding property and photocatalytic inactivity toward aqueous dye degradation process of F-doped CeO2 has suggested its potential use in cosmetic applications. Both F-doped CeO2 and CeO2 have been used as catalysts for oxidative coupling of benzylamines to imines in the presence of molecular oxygen under solvent-free conditions. F-doped CeO2 exhibited better catalytic efficiency than CeO2. The oxidation procedure using these catalysts is simple, environmentally benign, and solvent-free, and the catalysts are reusable.
An iron(II) bromide-catalyzed oxidative coupling of benzylamines with 2amino/hydroxy/mercapto-anilines has been developed, allowing the synthesis of a diversity of substituted 1,3-benzazoles in good to excellent yields. This transformation is compatible with a wide range of functional groups. The method is practical, economical and employs molecular oxygen as an oxidant.
A copper-catalyzed oxidative coupling reaction of o-phenylenediamines with 2-aryl/heteroarylethylamines using molecular oxygen as an oxidant has been developed. This approach provides a practical and direct access to construct quinoxalines in excellent yields at room temperature. The reaction has a broad substrate scope and exhibits excellent functional-group tolerance. This method could be easily scaled up and applied to the synthesis of biologically active molecules bearing a quinoxaline structural scaffold.
The efficient metal-free oxidative coupling of arylmethylamines with indoles has been developed using molecular oxygen as a green oxidant towards a novel rout of 3,3′-bis(indolyl)methanes (BIMs) synthesis.
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