Novel Catalyst Construcued From The Small Organic Molecule And Its Catalytic Performance For The Selective Oxidation Of Alcohols

The selective oxidation of alcohols into carbonyl compounds is one of the most important transformations in organic synthetic chemistry.Although traditional methods with stoichiometric amounts of oxidants are useful,large amounts of toxic waste are produced.From both economic and environmental viewpoints,the use of green oxidants,such as molecular oxygen as terminal oxidant,is the focus of great attention because dioxygen is inexpensive and water is produced as the only byproduct.However,direct oxidation of alcohols to the corresponding carbonyl compounds by molecular oxygen is difficult,because the oxygen is inert.This transformation can be achieved in the presence of suitable catalyst.Therefore,the key to the oxidation of alcohols with molecular oxygen is the choice of catalyst.Here,two novel catalysts were synthesized based on organic small molecule and its application for the selective alcohol oxidation using molecular oxygen as oxidant.A novel bioinspired bifunctional ligand incorporating metal-binding site and stable free radical has been synthesized and a practical Bpy-TEMPO/CuI/NMI/air system for the oxidation of alcohols to the corresponding aldehydes and ketones has been developed.With 1-octanol as model substrate,effects of various parameters(solvents,copper salts,bases)on the oxidation of 1-octanol were investigated in detail.With the optimized reaction conditions,the conversion of 1-octanol is 98%and the yield of 1-octanal is 95%by using 5 mol%CuI,5 mol%Bpy-TEMPO,10 mol%NMI,air balloon at room temperature for 6 h.The catalyst system features excellent activity for primary aliphatic alcohol oxidation and a high chemoselective oxidation of primary alcohols over the secondary alcohols.This oxidation process is readily amenable to larger-scale application.The interaction of the different components in the reaction mixtures was studied by UV-visible spectroscopy.The data indicated that Cu(?)existed throughout the reaction,Cu(?)(TEMPO-bpy)(NMI)can activate O2 to form an active species(Cu(?)-O2·--TEMPO-bpy)(NMI)in the presence of TEMPO.NMI has to be added in the above catalytic system.We have an idea that put NMI and TEMPO together as a bifunctional molecule.A series of new bifunctional imidazole-derived TEMPO catalysts were designed and synthesized.A new NMI-TEMPO/CuI/bpy/air system for the oxidation of alcohols to the corresponding aldehydes and ketones has been developed.With 1-octanol as model substrate,effects of various parameters(solvents,copper salts,ligands)on the oxidation of 1-octanol were investigated in detail.With the optimized reaction conditions,the conversion of 1-octanol is 98%and the yield of 1-octanal is 94%by using 5 mol%CuI,5 mol%NMI-TEMPO 1,5 mol%4,4'-Di-tert-butyl-2,2'-dipyridyl,air balloon at room temperature for 6 h.The catalyst system features excellent activity for primary aliphatic alcohol oxidation.The data of UV-visible spectroscopy indicated that Cu(I)existed throughout the reaction.