酸性离子液体催化合成草酸二乙酯

合成了4种咪唑基酸性离子液体，用于催化草酸和乙醇酯化反应合成草酸二乙酯。考察了影响反应的主要因素，确定最佳反应工艺条件为：采用Mim(CH₂)₃SO₃H]HSO₄离子液体为催化剂，反应温度为110 ℃，反应时间为90 min，n(乙醇)∶n(草酸)=4∶1。在此条件下离子液体循环使用4次，活性变化不明显，草酸二乙酯收率大于73%。此外，采用溶胶-凝胶法将Mim(CH₂)₃SO₃H]HSO₄离子液体固定到SiO₂上，用于催化酯化反应。结果表明，离子液体固定化后，其酸催化性能有明显提高，草酸二乙酯收率为84.8%，且催化剂具有较好的稳定性。

Synthesis of diethyl oxalate catalyzed by acidic ionic liquids

Four imidazolium-based acidic ionic liquids were synthesized and used as catalysts for the synthesis of diethyl oxalate by esterification of oxalic acid with ethanol. The effects of several operation conditions were investigated. The optimal reaction conditions were as follows：Mim(CH₂)₃SO₃H]HSO₄ as catalyst，reaction temperature 110 ℃，reaction time 90 min，mole ratio of ethanol and oxalic acid 4∶1，under such conditions the yield of diethyl oxalate was over 73%，and the ionic liquid could be recycled at least four times without obvious deactivation. Additionally，the ionic liquid Mim(CH₂)₃SO₃H]HSO₄ was immobilized on silica by the sol-gel method. The results showed that the supported ionic liquid exhibited higher catalytic performance than the unsupported one，with a yield of diethyl oxalate up to 84.8%.