Study On The Preparation Of Schiff Base Metal Complexes And Their Catalytic Selective Oxidation Of Cyclohexene

Cyclohexenone as an important chemical raw materials is widely used in organic synthesis,pharmaceutical chemistry,material preparation and so on.Currently,oxidation of cyclohexene to prepare cyclohexenone has generally low selectivity,which is easy to cause excessive oxidation.Therefore,it is of great theoretical value and industrial significance to study the selective oxidation of cyclohexene to produce cyclohexenone.Firstly,two heterogeneous catalysts were prepared by stepwise synthesis,M-L₁/Si O₂ and M-L₂(which M=Mn,Fe,Co,Ni,Cu.L₁=N-(3-trioxysilyl-propyl)-O-vanillin imine.L₂=terephthalaldehyde diethylenediamine)and used to catalyze cyclohexene oxidation,cyclohexenone showed high selectivity when Co was used as active sites.Then EA,ICP,FT-IR,UV-vis,TGA,XPS and BET were used to characterize the physicochemical properties of Co-L₁/Si O₂ and Co-L₂ catalysts.Secondly,the Co-L₁/Si O₂ and Co-L₂ catalysts were used to catalyze the aerobic oxidation of cyclohexene.Under the conditions of acetonitrile 5 m L,cyclohexene 6 mmol,oxygen pressure 0.2 MPa,reaction temperature 75?and 10 mg of Co-L₁/Si O₂,the conversion of cyclohexene was 33.02%,the selectivity of cyclohexenone was 62.50%,and the selectivity of cyclohexenol was 23.69%,and the total selectivity of cyclohexenone to cyclohexenol reached 86.19%.Furthermore,using Co-L₂ as catalyst,the conversion of cyclohexene was37.66%,the selectivity of cyclohexenone was 68.99%,the selectivity of cyclohexenol was14.60%,the total selectivity of allyl oxidation product was 83.59%under the conditions of acetonitrile 5 m L,cyclohexene 6 mmol,oxygen pressure 0.3 MPa,Co-L₂ 20 mg and reaction temperature 70?.Thirdly,research on the catalytic performance of Co-L₁/Si O₂ and Co-L₂ catalytic cyclohexene oxidation found that Co-L₂ catalysts have higher catalytic activity than Co-L₁/Si O₂.Co-L₂ catalyst was still able to catalyze the aerobic oxidation of cyclohexene at 60?,and Co-L₁/Si O₂ almost no longer reacted when the temperature was reduced to65?.Meanwhile,the re-use performance study of the catalyst found that the conversion of cyclohexene increased from 33%to 61%after Co-L₁/Si O₂ repeated use 5 times,and the selectivity of allyl oxidation products decreased from 86%to 57%.Furthermore,the conversion of cyclohexene(37-40%)and the selectivity of allyl oxidation products(80%)remained stable when Co-L₂ repeated use for 5 times.Finally,the bond energy of reactants,intermediates and products was calculated by DFT,and the reaction route of cyclohexene oxidation was inferred.Initially,oxygen is activated to react with cyclohexene to form the cyclohexene hydrogen peroxide intermediate product,and cyclohexene hydrogen peroxide is split to form cyclohexeneoxy radical,which further reacts with cyclohexene to form cyclohexenol.Furthermore,DFT calculation found that cyclohexenol was more easily oxidized than cyclohexene,and the result was that cyclohexenol could be oxidized to cyclohexenone.ln addition,the C-H bond energy of cyclohexene allyl group is lower than that of epoxy cyclohexane,so epoxy cyclohexane can not undergo allyl oxidation to produce the by-products 7-oxoheterocyclic[4.1.0]hept-2-ol,7-oxoheterocyclic[4.1.0]hept-2-one.While the production of the by-products7-oxabicyclo[4.1.0]heptan-2-ol and 7-oxabicyclo[4.1.0]heptan-2-one is mainly caused by epoxidation of cyclohexenone and cyclohexenol,so how to avoid epoxidation is the key to improving the selectivity of cyclohexene allyl oxidation.