Synthesis of dimethyl succinate catalyzed by ionic liquids

Seven kinds of ionic liquids,N-methyl-imidazolium bisulfate(HSO4),1-butyl-3-methyl imidazole phosphate(H2PO4),1-butyl-3-methyl imidazole bisulfate(HSO4),1-butyl-3-methyl imidazole tetrafluoroborate(BF4),N-butyl-pyridine bisulfate(HSO4),N-butyl-pyridine phosphate(H2PO4),N-ethyl-pyridine bisulfate(HSO4),were designed and synthesized.The synthesis of dimethyl succinate catalyzed by ionic liquids was studied for the first time.It was shown thatHSO4 had the best catalytic performance,and optimal conditions for the synthesis of dimethyl succinate were obtained,succinic acid and methanol molar ratio 1∶3.0,amount of catalyst 5%(g/g)of succinic acid,reaction temperature 70℃ and reaction time 2 h.Under the optimal conditions,the yield of dimethyl succinate was up to 91.83%,esterification rate was 96.32%.The catalyst was recycled 7 times without substantial decrease in activity.Moreover,compared to conventional industrial catalysts,ionic liquid catalyst had the superiority of smaller catalyst dosage,less by-product,mild reaction conditions,high yield,and recycled catalyst usage.Finally,the mechanism of esterification catalyzed by ionic liquids was discussed.