The oxidation of benzothiophene using the Keggin-type lacunary polytungstophosphate as catalysts in emulsion

A series of emulsion catalysts were successfully synthesized with quarternary ammonium cations and heteropolyanions, and they were characterized by TG/DTA, FTIR, 31P MAS NMR and EPR. The emulsion catalyst with intact Keggin-structure, [C18H37N(CH3)3]H2[PW12O40] (PW12), is inactive for benzothiophene (BT) oxidation with H2O2 as oxidant under atmospheric pressure at 30 °C. Moreover, the metal-substituted catalysts PW11M (M = Ti, Mn, Fe, Co, Ni and Cu) show rather low activity with the conversion less than 15% for BT oxidation. Whereas, the catalyst with mono-lacunary Keggin-structures, [C18H37N(CH3)3]5Na2[PW11O39] (PW11), could completely catalytic oxidize BT into the corresponding sulfone under the same conditions. After careful characterizations of the catalysts, it is found that only PW11 catalyst could effectively transform into the active polyperoxometalates species in the presence of hydrogen peroxide in non-polar solvent.

A catalyst [C18H37N(CH3)3]5Na2[PW11O39] (PW11), synthesized with quarternary ammonium cations and mono-lacunary Keggin-structures heteropolyanions, could completely oxidize BT into BT sulfone with H2O2 as oxidant under mild conditions in emulsion.Figure optionsDownload high-quality image (119 K)Download as PowerPoint slideResearch highlights▶ A series of emulsion catalysts were successfully synthesized. ▶ The catalyst with mono-lacunary structures shows high activity for BT oxidation. ▶ Metal-substituted catalysts show rather low activity for BT oxidation. ▶ PW11 catalyst could rapidly transform into the active polyperoxometalate.