Acidic Ionic Liquid Synthesis And Its Application In The Esterification Reaction

Due to their unique chemical and physical properties of nonvolatility, nonflammability, high thermal stability and wider electrochemical potential window, ionic liquids are widely applied in many research fields such as electrochemistry, organic synthesis, catalysis, separation chemistry as environment benign compounds in recent years. At present, research works about ionic liquids are focused on the synthesis and the application. In this paper, the main contents are as follows:1. The summary includes: the classification of ionic liquids; the synthetic method and quality of ionic liquids; the application of ionic liquid in organic synthesis, electrochemistry, separation chemistry etc.2. (1) Study on catalytic synthesis of propionates in ionic liquidsThe optimum reaction conditions for synthesizing methyl propionate in ionic liquids [Hmim]⁺BF₄^- were obtained by orthogonal experimental method.The optimum reaction conditions were: n(ionic liquids) : n (propionic acid) : n(methanol)=1:4:1; reaction temperature, 135℃; reaction time, 8 h.The yield of methyl propionate was about 71.2%. And the reusability of the catalyst was also studied. It showed that [Hmim]⁺BF₄^- was active under mild reaction conditions, non-corrosive and non-expendable.(2) Study on the synthesis of oxalates in ionic liquidsThrough the orthogonal experimental method, the optimum reaction conditions for preparing dimethyl oxalate in ionic liquids [Hmim]⁺BF₄^- were obtained. The optimum reaction conditions are as follows: n(ionic liquids) : n(oxalic acid) : n(methanol) = 1:1:5; oil-bath temperature, 130℃; reaction time, 6 h. The yield of dimethyl oxalate was 77.0%. Esterification of oxalic acid with ethanol, 1-propanol, 1-butanol with [Hmim]⁺BF₄^- as its catalyst were investigated under the same conditions, the yield of diethyl oxalate, dipropyl oxalate, dibutyl oxalate is respectively 79.4%, 81.7%, 84.8%. The catalytic ionic liquid system can be recycled 6 times without a significant decrease in catalytic performance. The ionic liquid [Hmim]⁺BF₄^- showed good catalytic activity to esterification reactions of oxalic acid with methanol, ethanol, 1-propanol, 1-butanol; with mild reaction, no corrosion and no waste acid.3. Thirteen ionic liquids based on 1-alkylationbenzimidazolium have been prepared, they are: 1 -methyl-3-H-benzimidazoliumtetrafluoroborate ([HmBim]⁺BF₄^-) 1 -ethyl-3-H-benzimidazoliumtetrafluoroborate ([HeBim]⁺BF₄^-) 1 -propyl-3-H-benzimidazoliumtetrafluoroborate ([HpBim]⁺BF₄^-) 1 -butyl-3-H-benzimidazoliumtetrafluoroborate ([HbBim]⁺BF₄^-) 1 -pentyl-3-H-benzimidazoliumtetrafluoroborate ([HpeBim]⁺BF₄^-) 1,2-methyl-3-H-benzimidazoliumtetrafluoroborate ([HmmBim]⁺BF₄^-) 1-ethyl-2-methyl-3-H-benzimidazoliumtetrafluoroborate([HemBim]⁺BF₄^-) 1-propyl-2-methyl-3-H-benzimidazoliumtetrafluoroborate ([HpmBim]⁺BF₄^-) 1-butyl-2-methyl-3-H-benzimidazoliumtetrafluoroborate ([HbmBim]⁺BF₄^-) 1-pentyl-2-methyl-3-H-benzimidazoliumtetrafluoroborate ([HpemBim]⁺BF₄^-) 1,2-ethyl-3-H-benzimidazoliumtetrafluoroborate ([HeeBim]⁺BF₄^-) 1-ethyl-2-propyl-3-H-benzimidazoliumtetrafluoroborate([HepBim]⁺BF₄^-) 1-ethyl-2-butyl-3-H-benzimidazoliumtetrafluoroborate ([HebBim]⁺BF₄^-)Their structures and compositions were characterized by FT-IR, ¹HNMR, elemental analysis. Synchronously, their melting point, solubility and thermal stability were determined. The results show that the ionic liquids exhibit high purity, excellent thermal stability, they have potential usage as alternatives to conventional organic solvents due to their special solubility and excellent thermal stability.Esterification of oxalic acid with methanol, ethanol, 1-propanol, 1-butanol with [HbBim]⁺BF₄^- as its catalyst were investigated, and the reusability of the catalyst was also studied. The experiment results indicate that good catalytic activity of ionic liquids [HbBim]⁺BF₄^- to esterification reactions, and the ionic liquid can be recycled 8 times without a significant decrease in catalytic performance.