WACKER-TYPE OXIDATION OF CYCLOHEXENE OVER PALLADIUM-SUPPORTED HETEROPOLY COMPOUNDS

Liquid phase oxidation of cyclohexene with O2 has been studied using Pd-supported heteropoly compounds and homogeneous catalysts. A Pd-supported Cs2.5H0.5PMo6W6O40 was found to be efficient for the catalytic oxidation of cyclohexene to produce cyclohexanone (Wacker-type oxidation) and cyclohexenone (allylic oxidation), whereas PdCl2-CuCl2 showed a very low activity under the same conditions. While the activity of Pd-supported Cs2.5H0.5.PMo6W6O40 decreased during the reaction, it was recovered by the heat treatment of the catalyst powder in helium or hydrogen. From the time course of the products and O2 pressure dependence, it was shown that the two products were formed through a parallel reaction. At 80-degrees-C and 8 atm of O2, turnover frequency (TOF) for the total products reached about 25 on the basis of Pd atom, which is greater than that for a homogeneous Pd(NO3)2-H3PMo6W6O40 system. The rate of the formation of cyclohexenone (allylic oxidation) was influenced by the pretreatment conditions. On the other hand, the rate for cyclohexanone (Wacker-type oxidation) was insensitive. These results support the different active sites for the two reactions.