Study On Lipase-catalyzed Preparation Of Caprolactone By Cyclohexanone

Polyε-caprolactone(PCL)is a new type of degradable material.It has many excellent properties compared with traditional plastics and metal materials.And it has received wide attention from various industries.Therefore,the research on its monomerε-caprolactone(ε-CL)has also become a top priority.There have been many reports on the synthesis ofε-caprolactone.Among them,the chemical synthesis methods have some safety hazards,and it will cause the waste of resources and a certain degree of damage to environmental safety and cleanliness.In contrast,the methods required for enzyme-catalyzed method synthesis are more moderate,and the catalyst can be multiply recovered and reused.This process is simple,feasible,and consistent with the recycling method advocated by green chemistry.This paper mainly studies the effects of various factors on the reaction system in the biocatalytic reaction,and finally determines the best experimental scheme.In this project,we has studied the relevant literature at home and abroad,and a new method for synthesizingε-caprolactone by the chemical-enzymatic cascade reaction of cyclohexanone mediated by immobilized lipase from T.laibacchii CBS5791 cells was developed.In the first step,in the presence of hydrogen peroxide,the lipase catalyzes the perhydrolysis of the activated acyl donor ethyl acetate to generate peracetic acid in situ;in the second step,peracetic acid oxidizes cyclohexanone to formε-CL.At the same time,we propose the existence of the third reaction:the byproduct acetic acid can be oxidized in situ by UHP under the catalysis of lipase to generate peroxyacetic acid,thereby forming a cycle.The immobilized preparation used here is prepared by purification and in situ immobilization.Compared with Novozym435 immobilized on a carrier by physical adsorption,the cross-linking immobilization is less likely to cause leaching of enzymes.The effects of various reaction parameters,such as the solvent,the initial concentration of cyclohexanone,the form of hydrogen peroxide,the temperature and the molar ratio of cyclohexanone to hydrogen peroxide were studied.The Baeyer-Villiger oxidation reaction of the immobilized T.laibacchii lipase-mediated chemo-enzyme synthesis ofε-CL was optimized by response surface methodology(RSM).It was finally determined that when the cyclohexanone concentration was 1.22 mmol/mL,the molar ratio of cyclohexanone and urea hydrogen peroxide(UHP)was 1:1.3,and the reaction was performed at 56.5℃,the highest yield ofε-CL was 98.06%,and the corresponding concentration was 1.2 mmol/mL.It was much higher than previous research.A best-fit quadratic polynomial model based on RSM experimental results was established,and the R~2 value of the equation was 0.9988,indicating that the model can predict the experimental results with high accuracy.The experimental results also show that the molar ratio of cyclohexanone to UHP has the greatest effect on the yield ofε-CL.According to the analysis of experimental results,we can conclude that there is an acetic acid cycle in the synthesis system ofε-CL,that is,the byproduct of acetic acid reacts with UHP to produce peroxyacetic acid and participate in the chemical oxidation process of cyclohexanone.This not only allows the by-product acetic acid to be consumed in situ,but also reduces the amount of UHP used in the reaction.