Study On Cobalt Catalyzed Wacker-type Oxidation Reaction Of Styrene And Its Derivatives

Aromatic ketone compounds,a very important class of chemical products and organic synthesis intermediates,were widely used in food,organic synthesis,coatings,fragrances,cosmetics,medicine and polymer materials.The reaction in which metallic palladium oxidizes olefins to ketones was called the Wacker reaction.Although some good results have achieved,the reaction system still suffers from some shortcomings,such as expensive catalysts were used and a large amount of copper and chlorine-containing wastes were produced which causes environmental pollution.Therefore,the development of sustainable,new non-noble metal catalysts is of great significance.On the basis of the preliminary works of our group,a series of single atom cobalt catalysts supported on activated carbon were prepared and were successfully applied to the Wacker-type oxidation.Under clean conditions,the styrene and its derivatives and 1,1-disubstituted styrene and its derivatives were converted to aromatic ketones and corresponding tertiary alcohols,respectively.The active site of the reaction was determined by analysis of the catalyst surface composition and control experiments.The specific work as follows:（1）A series of single atom cobalt catalysts were easily and efficiently prepared by high-temperature pyrolysis at different temperatures when commercially available activated carbon was used as the supporter,Co（OAc）₂·H₂O was selected as the cobalt source and 1,10-phenanthroline was chosen as the ligand.The prepared catalysts were denoted as Co-N/C-600,Co-N/C-700,Co-N/C-800 and Co-N/C-900,respectively.Using styrene as model substrate,it was found that Co-N/C-800 showed the best activity after large amount of experimental condition screenings were conducted.The acetophenone can be obtained with a yield of 95.8%after 6 h under 0.4 MPa O₂ at 150℃,when the preferred catalyst was used with isopropanol as solvent.Subsequently,when the substrate was expanded under the further optimal conditions,it was found that the catalytic system has great functional group tolerance.Regardless of olefins with electron-withdrawing groups or electron-donating groups attached to the benzene ring,as well as the polycyclic and fused-ring olefins,the corresponding products with medium or high yield can be obtained.When 1,1-disubstituted olefins were selected as substrates,the yields of corresponding tertiary alcohols were reached to 99%.The isotope labeling experiment proved that one hydrogen on acetophenoneα-C comes from isopropanol.（2）The pore size and BET surface area of this series of catalysts were calculated according to the nitrogen adsorption-desorption curve,which are mesoporous materials.The cobalt nanoparticles and single atom cobalt were observed in catalysts simultaneously with the help of electron microscope and XAS.The XPS was used to further determine the chemical environment of single atom cobalt.The result of KSCN titration experiment proved that the active site of the catalyst is single atom cobalt instead of cobalt nanoparticles.The reaction mechanism was studied deeply by a series of experiments designed reasonably and the possible reaction mechanism was proposed in combination with related literature.The research of our works has realized the Wacker-type reaction catalyzed by single atom cobalt catalyst in a green,clean and efficient way,which has theoretical and practical application significance.