Esterification catalyzed by ionic liquids of imidazolium hydrogen sulfate

Esterification of alcohols with carboxylic acids in six ionic liquids,including 1-methylimidazolium hydrogen sulfate(HSO4),1-alkyl-3-methylimidazolium hydrogen sulfate(HSO4,n=2,4,8,12),1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate([C3SO3Hmim]HSO4) used as catalysts had been investigated.The relationship between the substituent groups attached to the imidazole ring and the catalytic activity of ionic liquid for esterification were studied.[C3SO3Hmim]HSO4 with the strongest acidity had the best catalytic activity for all cases of esterification.Under the reaction conditions for synthesizing three acetates,the ionic liquids in the reaction system with phase-separation had better catalytic activity than those without phase-separation when the reaction was brought to completion.The test results showed that the substituent group attached to the imidazolium cation could affect the miscibility with the related components existing in the reaction to influence the catalytic activity and the biphasic behavior.