A modified Wacker catalysis using heteropolyacid: Interaction of heteropolyanion with Cu(II) in cyclohexene oxidation

Abstract Palladium(II)-copper(II)-heteropolyacid catalyst system for the Wacker type oxidation of cyclohexene to cyclohexanone was studied. Addition of heteropolyacid to chloride ion-free Pd(II) Cu(II) catalyst system resulted in great increase of catalytic activity in cyclohexene oxidation. A catalyst system of Pd(NO 3 ) 2 CuSO 4 H 3 PMo 12 O 40 combination showed much higher activity and selectivity compared with Pd(NO 3 ) 2 CuSO 4 or Pd(NO 3 ) 2 H 3 PMo 12 O 40 combination. The spectroscopic changes of the heteropolyanion species in the catalytic systems were monitored by IR, UV-Vis and ESR methods. The spectroscopic data supported the existence of the interaction between Cu species and heteropolyanion. The interaction was proposed to be related with the electron transfer and di-oxygen reduction for the facile re-oxidation of Pd(0) to Pd(II) in the catalytic reaction cycle.