A series of functional binuclear ionic liquids based on bis-(3-methyl-1-imidazole)butylidene double P-toluene sulfonic acid salt (Im-PTSA), bis-(3-methyl-1-imidazole)butylidene double bisulfate (Im-HSO₄), bis-(1-pyridine)butylidene double p-toluene sulfonic acid salt (Py-PTSA), bis-(1-pyridine)butylidene double bisulfate (Py-HSO₄) were synthesized by a two-step proceeding and their structures were characterized by FT-IR and ¹H NMR spectra. Their thermal stabilities were characterized by TG. In addition, the acidity and solubility of functional binuclear ionic liquids were also studied. The catalytic activity of the binuclear ionic liquids for the esterification of succinic acid with ethanol was measured. The results show that under the optimized conditions of n(succinic acid):n(ethanol)=1:3, catalyst used dosage 1.90% (wt), 70 ℃ and 2.5 h, the yield of diethyl succinate reached 93.6% and the selectivity was near up to 100%. Im-PTSA was reused at least 8 times without significant decrease in activity after drying under vacuum. Austenitic stainless steel 316L was used for conducting the corrosion test under the above esterificaion condition, the corrosion rates of the steel plates dipped in the systems with these ionic liquids were less than one tenth of that with sulfuric acid. Fischer esterification of monocarboxylic acids and dicarboxylic acids with different alcohols was observed on using Im-PTSA as catalyst which gave high product yield and selectivity. Use of such a reaction catalyst should be appreciated for its convenient separation.

Key words: binuclear ionic liquid, esterification, catalyst, diethyl succinate, corrosion