Palladium(II) Sulfate-Heteropoly Acid-catalyzed Oxidation of Cycloolefins in Liquid Phase

Abstract Heteropoly acid (HPA) was used as an oxidant in the Wacker catalyst system. Among the catalyst systems examined, the PdSO4–H3PMo6W6O40 catalyst system showed the highest activity with regard to the oxidation of cycloolefins, particularly cyclopentene and cyclohexene, to the corresponding cyclic ketones. The largest total turnover number with respect to Pd2+ was found to be 85 in water containing 20% N-methylformamide by volume. The initial rate of cyclohexene oxidation was expressed as V o=k[Cyclohexene]1.0[PdSO4]1.0[HPA]0[O2]0. The rate-determining step was suggested as being where cyclohexene was oxidized to cyclohexanone by Pd(II) salt. The apparent activation energy was 7.8 kcal mol−1 (1 cal=4.18 J). In the catalytic oxidation of cycloolefins (CnH2n−2: n=5, 6, 7, and 8), the yield of alicyclic ketone decreased as the carbon number n increased. Methyl-substituted cyclohexenes exhibited lower reactivities than cyclohexene.