Catalytic Synthesis of Diethyl Pimelate with Functionalized Ionic Liquids

Abstract

An acidic ionic liquid, [Emim]HSO₄, was prepared and used as solvent and catalyst in the esterification reaction of 1,7-pimelic acid and ethanol. The esterification products could be easily separated from the reaction system. The effects of the reaction conditions on the reaction results, such as the amount of catalyst, molar ratio of acid and ethanol, reaction time, were examined and the optimal conditions were obtained through orthogonal tests based on single-factor experiments. The optimal conditions were as follows: n(C₂H₅OH):n(C₇H₁₂O₄) = 3:1, 2 mL of catalyst, reaction time for 5 h at 383.15 K. Under the optimal reaction conditions, the diethyl pimelate was obtained in 96.37 % yield. The acidic ionic liquid, [Emin]HSO₄ could be reused for 5 times and the yield of diethyl pimelate were more than 95.18 % after repeating 5 times of catalyst applications. Compared with the traditional catalyst of concentrated sulfuric acid, the ionic liquids had the advantages of good chemical stability, non-pollution, less side reaction, good repeatability and not using organic solvent as hydrated solvent, etc.