Synthetic Method of Diethyl Maleate

 Diethyl maleate often referred to as DEM, CAS Number: 141-05-9, molecular formula: C₈H₁₂O₄ , Molecular weight: 172.1785, mainly used as polymer compound monomers, pesticides, medicines, perfumes, water quality stabilizers (organic polycarboxylic acid phosphonic acid compounds) intermediates, At present, it is mainly used in the production of organophosphorus pesticide malathion (marathon) ^[1].

Diethyl maleate is mainly produced by the esterification of maleic anhydride and ethanol in the presence of sulfuric acid. This process has two types: normal pressure with benzene esterification and negative pressure without benzene esterification.

1. Normal pressure with benzene esterification:Add a certain amount of benzene and ethanol into the esterification reaction pot, put in maleic anhydride, add concentrated sulfuric acid dropwise with stirring, and heat through jacket steam to make the reactants undergo esterification reaction at about 75°C. The generated water, benzene and ethanol are removed by ternary azeotropic distillation, and the benzene and ethanol liquid in the upper layer is refluxed into the reaction pot. After about 13 to 14 hours, when the temperature at the top of the distillation tower rises to 68.2°C and the water level in the lower layer of the separator no longer rises, it indicates that all the water in the reaction pot has been evaporated and the esterification reaction is complete. Stop reflux, continue to distill to 95-100°C, and distill benzene and ethanol. Cool down to about 50°C, neutralize with 5% sodium carbonate aqueous solution, wash with water and remove residual benzene and ethanol in vacuum to obtain the product diethyl maleate.

2. Negative pressure without benzene esterification: The maleic anhydride and ethanol are esterified under the action of concentrated sulfuric acid, and the ethanol and the water produced by the reaction are carried out in a gaseous state under a certain vacuum and temperature, and then the ethanol is separated through a fractionation tower to reflux and esterify, so that the reaction tends to complete. This method can shorten the reaction cycle, increase the yield and product quality, and improve the operating environment.

In addition, the use of cation exchange resins to produce diethyl maleate has also been reported, but the low cost performance of ion exchange resins makes it difficult to achieve industrial applications ^[2].

References

[1] Sun Zaichen, Tian Junjie, Zhang Xuezhong, etc. A method for preparing diethyl maleate by ion-exchange membrane coupling technology [P]. Chinese Patent: CN108794332A, 2018-07-26;

[2] Guo Hongyun, Jin Chunhui, Zhang Qiyuan, et al. A method for synthesizing diethyl maleate catalyzed by an acidic ionic liquid [P]. Chinese Patent: CN111269117A, 2020-02-28;