Epoxidation Of Olefins With Molecular Oxygen To Prepare Epoxides In Organic Systems

Epoxides are important industrial chemicals and organic synthons.They are widely used in the pharmaceutical,fine chemical,material and other industries.Oxygen is one of the green and sustainable resources.However,there are some problems in preparing epoxides with molecule oxygen,such as harsh reaction conditions,poor selectivity,narrow scope of substrates,easy deactivation of catalysts,and the need for a large amount of co-reductants.In this paper,molecular oxygen is activated by photocatalysis and cumene autoxidation,and used in the field of epoxidation.(1)It was found that the compounds containing formamidine structural unit can promote the aerobic epoxidation of α,β-unsaturated ketones induced by visible light in the presence of visible light,photosensitizers,and molecular oxygen.48～94%yields of 19 corespounding epoxides were obtained after 96 h at 10℃ in the presence of tetramethylguanidine under LED white light(10 W,4000 K)by using molecule oxygen as the oxidant,H2TPP as the photosensitizer and 1,4-dioxane as the solvent.It was suitable for cyclic α,β-unsaturated ketones as well.Photo-microreactors technology was also applied based on the batch reaction,achieving the photocatalytic gas-liquid two-phase flow reaction.As a result,90%isolated yield was obtained with a residence time of 4.6 h,which shorten the reaction time greatly.Finally,the possible reaction mechanism was proposed based on experiments and verified by DFT calculations.(2)Developed a method to prepare α,β-epoxy ketones based on autoxidation of cumene.61～99%yields of epoxides were obtained using cumene as the solvent,K2CO3 as the base and air as the oxidant.Eight recycling experiments were carried out.K2CO3 was reused for 8 times with a stable activity and solvent was recovered with a recovery rate of above 80%at every cycle.Mechanism research shows that both cumene peroxy radical(ROO·)and cumene hydrogen peroxide(CHP)generated in-situ could react with olefins to yield the corresponding epoxides.(3)Kinetic analysis for preparing α,β-epoxy ketones based on autoxidation of cumene was made.a.The activation energy for the reaction of cumene peroxy radical(ROO·)and cumene(CM)to generate CHP is ΔEa5=62.54 kJ/mol.The oxygen concentration in the reaction solution was reduced with increasing temperature,thereby affecting the peroxidation rate.b.The activation energy for the epoxidation of chalcone with cumene hydrogen peroxide(CHP)is ΔEa7=14.97 kJ/mol.c.The activation energy for the epoxidation of chalcone with peroxy radical(ROO·)is ΔEa6=51.01 kJ/mol.ΔEa5 is bigger than ΔEa6,indicating that cumene peroxy radical(ROO·)is more inclined to react with chalcone to form an epoxide.(4)The substrates scope of epoxidation based on autoxidation of cumene was extended to olefins without conjugated double bond.30～77%conversion and 65～96%selectivity could be obtained by using styrene derivatives as substrates.Mechanism research shows that cumene peroxy radical(ROO·)is the major epoxidation reagent.