硅胶固定化咪唑酸性离子液体的合成及在酯化反应中的应用

为了减少离子液体用量,缩短反应时间,提高酯化反应的催化效率,该文以硅胶为原料与-γ(2,3-环氧丙氧基)丙基三甲氧基硅烷(KH-560)反应,合成了环氧基硅烷化硅胶,再与1-甲基咪唑硫酸氢盐发生开环反应,制备了一种硅胶固定化1-甲基咪唑硫酸氢盐离子液体。探讨了该离子液体在无机酸促进下对合成乙酸乙酯反应中原料摩尔比、酸的用量及离子液体用量等因素对反应的影响。实验表明,当n(乙醇)∶n(乙酸)=1.5∶1,该固定化离子液体用量为1.00 g,盐酸用量为2.0 mL时,乙酸乙酯的最高产率可达90.0%。固定化离子液体重复使用5次,酯的产率由90.0%降至85.1%。将该固定化离子液体应用于催化乙酸异戊酯、苯甲酸乙酯、草酸二乙酯、乙酸正丁酯和马来酸二乙酯的合成,酯的产率比仅用盐酸单组分催化分别提高了20.4%、25.6%、28.2%、22.3%和16.1%。通过简单滤除就可实现离子液体与产物的分离。

Synthesis and Applications in Esterification of Silica-immobilized Imidazolium Acidic Ionic Liquid

In order to decrease the amount of ionic liquid,and the reaction time as well as to improve the catalytic efficiency in esterification,a novel silica-immobilized 1-methylimidazolium hydrogensulfate acidic ionic liquid was used.The silicagel was firstly reacted with γ-glycidoxypropyltrimethoxysilane(KH-560) to form epoxy-silane silica gel.Subsequently,it was reacted with 1-methylimidazolium hydrogensulfate to form a silica-immobilized 1-methylimidazolium hydrogensulfate acidic ionic liquid.The catalytic esterification efficiency of the ionic liquid promoted with inorganic acid is studied under different conditions such as the proportion of the raw material,the amounts of acid and the ionic liquid.The experimental result showed that the yield of ethyl acetate was 90.0% when the molar ratio of alcohol to acid was 1.5∶1,the quantity of HCl was 2.0 mL and the ionic liquid was 1.00 g.After the ionic liquid was reused in the fifth times under the same conditions,catalytic effect of the ionic liquid did not change significantly and the yield of ethyl acetate decreased from 90.0% to 85.1%.When the ionic liquid was used,the yield of isoamyl acetate,ethyl benzoate,ethyl oxalate,n-butyl acetate and diethyl maleate increased 20.4%,25.6%,28.2%,22.3%,and 16.1% respectively in comparison with the case when HCl was used alone.The esterification products could be easily separated in high yield from the reaction system by the simple phase separation.