New Bronsted-Acidic Ionic Liquids Based on 8-hydroxyquinoline Cation as Catalysts for the Esterification Reaction of n-hexylic acid

摘要

Five new acidic ionic liquids were firstly synthesized from 8-hydroxyquinoline and five kinds of acid such as H_2PO_4, H_2SO_4, CH_3SO_3H, TSOH, HBF_4 by one-pot method. The structures of the synthesized compounds were characterized by ~1H NMR, IR and MS. Acidities of the ILs was determined by Hammett acidity with the method of UVVis spectroscopic measurement. Because of the combinational advantages of homogeneous and heterogeneous catalysis, these new catalysts showed good reactivity under mild conditions and recoverability by simple filtration after reaction. The yield of esterification reaction was measured by GC. The acidity order of the novel ILs is (HSO_4)~- ＞ (BF_4~)- ＞ (CH_3SO_3)~- ＞ (TSO)~- ＞ (H_2PO_4)~-. The order of acidity of ILs were shown in the result of acidities of the ILs and the yield related the ILs showed the same trend. Therefore, The ionic liquid with (HSO_4)~- as anion exhibited the best catalytic performance. The conversion yield of nhexylic acid was up to 91.4% under the conditions.