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.