Cobalt–iron magnetic composites as heterogeneous catalysts for the aerobic oxidation of thiols under alkali free conditions

Abstract

Cobalt–iron magnetic composites prepared by the thermal treatment of an iron oxide-rich soil in the presence of sucrose and cobalt(II) sulfate are efficient heterogeneous catalysts for the liquid-phase aerobic oxidation of thiols into disulfides. The materials have been characterized by Mössbauer spectroscopy, XRD, N2 adsorption–desorption, and elemental analysis. It has been shown that the isomorphic substitution of iron by cobalt occurs preferentially in the framework of the wüstite (FeO) phase and strongly affects the catalytic behavior of the material. The choice of a solvent is critically important for the efficiency of the reaction. In weakly basic solvents, such as dimethylformamide and dimethylacetamide, disulfides can be obtained in near-quantitative yields at low catalyst loading (0.008mol%). A significant practical advantage of this environment-friendly process is the use of inexpensive magnetically recoverable materials as catalysts and oxygen as a final oxidant as well as mild alkali free conditions. Of particular note are the stability of the catalyst toward leaching and the possibility of catalyst recycling without any special treatment.