Direct Synthesis of Amides from Oxidative Coupling of Benzyl Alcohols or Benzylamines with N-Substituted Formamides Using a Cu-Fe-Based Heterogeneous Catalyst

摘要

Here we report a highly active and recyclable Cu- Fe based heterogeneous catalytic system for the oxidative coupling of benzyl alcohols as well as benzylamines with N-substituted formamides. The Cu- Fe Metal Oxide (Cu- Fe MO) catalyst was prepared by a co-precipitation method and was characterized by X-ray diffraction ( XRD), X-ray photoelectron spectroscopy ( XPS), Energy-dispersive X-ray spectroscopy (EDS), Field Emission Gun-Scanning Electron Microscopy (FEG-SEM) and N2 physical adsorption techniques. The catalytic activity of the asprepared Cu- Fe MO catalyst was evaluated towards amidation reactions and a broad spectrum of aromatic amides have been synthesized in good to moderate yields by oxidative coupling of benzyl alcohols or benzylamines bearing various substituents with N-substituted formamides. The control experiments revealed that the benzyl alcohol or benzylamine gets converted to an acyl radical and on the other side the N-substituted formamides form an aminyl radical in presence of the catalyst and tert-Butyl hydroperoxide (TBHP). Successive coupling of the in-situ generated acyl and aminyl radicals affords the desired product amide. Furthermore, the heterogeneous Cu- Fe MO catalyst recycled for four times towards the amidation of benzyl alcohol and the fidelity of the spent catalyst has been confirmed by XRD analysis.