阳离子结构对磺酸基离子液体酸强度的影响规律

Influence Rule of Cationic Structure on Acid Strength of Sulfonic Ionic Liquids

采用UV-Hammett指示剂联用法,以对硝基苯胺为指示剂,考察了阴离子为硫酸氢根,阳离子分别为三乙胺、N-甲基咪唑、吡啶或己内酰胺上带有丙烷基磺酸或丁烷基磺酸的8种磺酸基功能化离子液体的酸强度。结果表明,同一种离子液体的浓度越大,其酸强度越大,但不同离子液体间的相对酸强度大小顺序与离子液体的浓度无关;含氮母体化合物不同的磺酸基离子液体按酸强度由大到小排列的顺序为己内酰胺类、吡啶类、咪唑类、三乙胺类,当含氮母体化合物相同时,磺酸基的烷基侧链越长,则酸强度越大;相比于侧链长短对酸强度的影响,含氮母体化合物种类的影响更为明显。N-(4-磺酸基)丁基-咪唑硫酸氢盐、N-(4-磺酸基)丁基-己内酰胺硫酸氢盐、N-(4-磺酸基)丁基-吡啶硫酸氢盐、N-(3-磺酸基)丙基-吡啶硫酸氢盐、N-(4-磺酸基)丁基-咪唑硫酸氢盐和N-(3-磺酸基)丙基-咪唑硫酸氢盐6种离子液体在甲醇中的酸强度均比浓硫酸的大;但在水中,只有前5种离子液体的酸强度大于同浓度硫酸的酸强度。

Eight SO3H-functional Brnsted acidic ionic liquids（ILs）with different nitrogen function groups were prepared and their acid strengths were investigated by UV-Hammett combined method with p-nitroaniline as indicator.The results demonstrated that the acid strength of the ILs increased with the increase of their concentration, while their acidity order was irrelevant to the concentration.The acidity descend of the eight acidic ILs with different nitrogen groups was in the order of the IL with caprolactam group,pyridine group,N-methyl imidazole group,trimethylamine group,respectively.For the ILs with same nitrogen functional group,their acid strength increased with the alkyl chain being longer.Compared with the effect of alkyl chain length on the acid strength of IL,the effect of nitrogen functional group type was more obvious.In methanol,N-（4-sulfonic group）butyl-hydrogen sulfate imidazole,N-（4-sulfonic group）butyl-caprolactam hydrogen sulfate,N-（4-sulfonic group）butyl-pyridine hydrogen sulfate,N-（3-sulfonic group）propyl-pyridine hydrogen sulfate, N-（4-sulfonic group）butyl-hydrogen sulfate imidazole and N-（3-sulfonic group）propyl-hydrogen sulfate imidazole showed the character of super acid,however,in water only the first five showed the character of super acid.