| Six POM which contain one Pb and different number of Mo atoms have synthesized start from the well-known Dawson framework POM(P2W18 and P2W16). The IR and UV indicate that all the 6 compounds still remain basically characteristic of the Dawson structure. The TG and EA suggest their molecular formulas are: K10P2W16MoPbO62 ·10H2O ,K8H2P2W15Mo2PbO62 ·11H2O ,K10P2W14Mo3PbO62 ·10H2O ,K8H2P2W13Mo4PbO62 ·8H2O ,K8H2P2W12Mo5PbO62·9H2O 和K18[Pb(P2W16MoO61)2]·13H2O。The studies on redox properties of these POM in aqueous solution were made by polarography. It is noteworthy that their oxidizing power are different to the P2W18,especially for the P2W(17-n)MonPb(n =1～5) series. The oxidizing power of the series of POM is much strong than the P2W18,farthermore their oxidizing power increases as Mo atom number increase. Seven POM catalyze the oxidation of cyclohexene to adipic acid with 30% aqueous hydrogen peroxide, with P2W(17-n)MonPb gave identical yields and performing much better than Pb(P2W16Mo)2 and P2W18, Pb(P2W16Mo)2 led to lower yields(around 67.6%) but much better than P2W18(around 60.7%). The effects of temperature, catalyst loading, reaction time and molar ration of H2O2 to the substrate on the reaction were studied,and the reaction condition were optimized. When 10mmol cyclohexene been used, 95 ℃, 12h, 0.01mmol P2W12Mo5Pb, and 60mmol 30% aqueous hydrogen peroxide is a better reaction condition. Activated carbon supported P2W12Mo5Pb catalyst were investigated, when organic solvents(t-BuOH) been used , Activated carbon supported P2W12Mo5Pb led to a high yields(around 72%), and the yields have a very little decrease after the catalyst reuse 6 times. |
