May 23, 2011
This catalyst promotes the air oxidation of olefins to ketones. A catalytic air oxidation of an olefin directly to a ketone would be an important development for the petrochemical industry. Whereas oxidizing ethylene to acetaldehyde via the Wacker process is a well-known direct catalytic oxidation process, similar methods for directly manufacturing ketones in one step from the corresponding olefin have eluded commercialization.
R. Glaser and colleagues found a catalyst system that can convert olefins to ketones in good conversion and selectivity. The model used by the inventors is the conversion of cyclohexene to cyclohexanone, a precursor to adipic acid and caprolactam. The conventional routes to cyclohexanone are cyclohexane oxidation and phenol hydrogenation. The cyclohexane route is not very selective, and the phenol route uses a costly starting material.
The disclosed catalyst system is based on a mixture of Pd(OAc)2 and a heteropolyacid encapsulated in mesoporous silicate MCM-41. In one example, the catalyst consists of 10 wt% Pd(OAc)2 and 15 wt% ammonium molybdovanadophosphate in MCM-41). A mixture of 2 mmol cyclohexene, 4.5 mL MeCN, 0.5 mL H2O, 38 mg p-toluenesulfonic acid, and 100 mg of the catalyst mixture is charged into a glass tube that is inserted into an autoclave. The autoclave is pressurized with 2 MPa of air at 50 °C for 6 h. Cyclohexene conversion is 96.7%, and selectivity to cyclohexanone is 94.0%.
One of the challenges for this route to cyclohexanone will be to find a cost-effective way to convert benzene to cyclohexene. (Sumitomo Chemical [Tokyo]. US Patent 7,939,692, May 10, 2011; Jeffrey S. Plotkin)