Oxidation of cyclohexene into adipic acid in aqueous dispersions of mesoporous oxides with built-in catalytical sites

Abstract

Reactant incompatibility is a common problem in organic chemistry. This study investigates the use of concentrated aqueous dispersions of mesoporous oxides to overcome incompatibility. Oxidation of cyclohexene into adipic acid using aqueous hydrogen peroxide as oxidant has been performed in a range of ordered and disordered mesoporous materials. The different mesoporous oxides have been characterised with diffraction techniques (XRD and SAXS), electron microscopy (TEM and SEM) and nitrogen adsorption isotherms (BET and BJH methods). The catalyst used in the reaction was either soluble sodium tungstate added to a reaction system based on mesoporous silica, alumina or a silica/alumina mixture; or a catalytic oxide, tungsten oxide or titania, present in the framework of the mesoporous material. Tungsten oxide, either used as the sole oxide material or as a mixed oxide with silica turned out to be very efficient and gave almost quantitative yield of adipic acid. A major advantage with having the catalyst chemically incorporated in the walls of the porous material is that it can be easily reused. The results from recycling experiments show that the catalytic activity is retained.