Cesium-Exchanged Lacunar Keggin Heteropolyacid Salts: Efficient Solid Catalysts for the Green Oxidation of Terpenic Alcohols with Hydrogen Peroxide

In this work, an innovative and green oxidative process to convert renewable and abundant raw material to more value-added fine chemicals was developed. Hydrogen peroxide, an environmentally benign oxidant, was used in Cs-exchanged lacunar Keggin heteropolyacid salts-catalyzed oxidation reactions of the terpenic alcohols (i. e., nerol was the model molecule). The activity of most outstanding catalyst (Cs8SiW11O39) was compared with various catalysts. Epoxides and aldehydes, which are an attractive feedstock for fragrance and pharmaceutical industries were selectively obtained. Lacunar Keggin heteropolyacid salts containing cesium as the counter ion (i. e., Cs7PW11O39, Cs7PMo11O39 and Cs8SiW11O39) were easily synthesized and characterized by infrared spectroscopy, powdered X-rays diffraction, X-rays dispersive spectroscopy, scanning electronic microscopy, thermal analysis, porosimetry analyses, diameter and pores distribution. The influences of the main reaction variables such as catalyst concentration, the stoichiometry of the reactants and reaction temperature were evaluated. The reaction scope was successfully extended to the other terpenic alcohols. The Cs8SiW11O39 was the most active and selective lacunar salt. After five cycles of successive reuse, no loss of catalytic activity or selectivity was observed.