Three new protic ionic liquids based on morpholinium including morpholinium hydrogen sulfate ([Hnhm]HSO4), 4-methylmorpholinium hydrogen sulfate ([Hnmm]HSO4) and 4-(3-sulfopropyl)mor-pholinium hydrogen sulfate ([C3SO3Hnhm]HSO4) were synthesized and characterized. Their acidities and catalytic activities for the esterification of chloroacetic acid (CAA) with ethanol were examined and com-pared with other three SO3H-functionalized ionic liquids with various N-heterocycles, 1-(3-sulfopropyl) pyridinium hydrogen sulfate ([C3SO3Hpy]HSO4), 1-methyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) and 1-(3-sulfopropyl)-2-pyrrolidonium hydrogen sulfate ([C3SO3Hnhp]HSO4). The catalytic performance of SO3H-functionalized ionic liquids could be much better than that of non-SO3H- functionalized [Hnhm]HSO4 and [Hnmm]HSO4, as good as or even better than that of sulfuric acid as
catalyst. Under the optimized conditions of n(EtOH)∶n(CAA)∶n([C3SO3Hnhm]HSO4)＝1.3∶1∶0.2, 80 ℃, and 3 h, the yield of ethyl chloroacetate reached 93.4%. [C3SO3Hnhm]HSO4 was reused at least 9 times without significant decrease in activity after drying under vacuum. The esterifications of acetic acid with various alcohols in [C3SO3Hnhm]HSO4 have also been investigated. Good yields and selectivities were ob-tained, and all the produced esters could be easily recovered due to their immiscibility with the ionic liquid. In addition, Austenitic stainless steel 316 was used for conducting the corrosion test under the above esteri-ficaion condition. Although the acidities of SO3H-functionalized ionic liquids were close to that of sulfuric acid, the corrosion rates of the steel plates immersed in the systems with these ionic liquids were less than one third of that with sulfuric acid.

Key words: SO3H-functionalized, esterification, ionic liquid, ethyl chloroacetate, morpholinium