Heteropolyacid-conjugated chitosan matrix for triphase catalyst

H3PW12O40 (12-phosphotungstic acid; PWA) is efficient catalysts for the selective oxidation of alkanes, aldehydes, and perfluorinated acids. However, PWA molecules are high solubility in water and this property has been making it difficult to utilize as an industrial catalyst. In this study, the water-insoluble PWA-conjugated chitosan matrix was prepared by mixing the aqueous PWA and chitosan solutions. This conjugate matrix was constructed by the electrostatic interaction between amino group of chitosan and negative charge of PWA and showed the thermal stability at <100 °C. In addition, the PWA-conjugated chitosan matrix indicated the property for triphase catalyst as epoxidation of allylic alcohols, such as cinnamyl alcohol, farnesol, and so on. The isolated yield of epoxidation with the conjugate matrix was as same as that of pure PWA. Furthermore, since this conjugate matrix did not dissolve in water, matrices could easily separate from the reaction solvent and recycle more than 3 times. Therefore, the PWA-conjugated chitosan matrices may have a potential to utilize the novel catalyst for the epoxidation of various allylic alcohols.