Preparation Of Novel Ionic Liquids And Their Applications In Organic Reactions

Ionic liquids(ILs) are kinds of salts that existed in liquid form at room temperature or around and composed of an organic cation and an inorganic or organic anion. ILs present many advantages including low melting point, wide liquid temperature range, low vapor pressure, high solubility, easy to recycle, strong modification, good catalytic reactions performance, etc. With the further research, ILs have been widely used in organic reactions as green solvents and catalysts. Encouraged by the significant achievements of ILs, this paper designed and prepared two types of ionic liquids based on triethanolamine(TEA) and 1,4-diazabicyclo[2.2.2]octane(DABCO) and explored the applications of the prepared ionic liquids in the synthesis of bis-indolylmethanes, Knoevenagel condensation reaction and aza-Michael addition reaction.Firstly, a class of acidic ionic liquid [TEOA][X] and a class of basic ionic liquids [DABCO-PDO][X] were designed and synthesized taking triethanolamine(TEA) and 1,4-diazabicyclo[2.2.2]octane(DABCO) as the raw materials through the two-step method. The prepared ionic liquids were confirmed and characterized by 1H NMR, 13 C NMR and elemental analysis. Acidity tests of acidic ionic liquid [TEOA][X] were conducted based on Hammett function.Secondly, the prepared acidic ionic liquids [TEOA][X] were used to catalyze synthesis of bis-indolylmethanes and Knoevenagel condensation reaction of complex active methylene compounds and aromatic aldehydes. The best catalytic performance for the synthesis of bis-indolylmethanes was obtained at room temperature with 10 mol% [TEOA][HSO4] without any solvent and the ionic liquid could be reused for 5 times, still remained high catalytic activity. Compared with previous reports, this catalytic system showed a lot of advantages. At room temperature, taking methanol as the reaction solvent, 2 mol% ionic liquid [TEOA][HSO4] as catalyst, Knoevenagel condensation products were got in 91%-98% yields within relatively short times(3-9 min). Additionally, the reaction system had a good spatial selectivity that all products obtained were E-geometry and the catalyst could be recycled more than 6 times. The proposed reaction mechanisms were given and some experimental validations were carried out.Finally, aza-Michael addition of ?, ?-unsaturated amides catalyzed by basic ionic liquids [DABCO-PDO][X] was studied. The optimum conditions were determined as 10 mol% ionic liquid [DABCO-PDO][OAc] at room temperature under solvent-free condition. The reactions preceded smoothly giving 70%-95% product yields within 1-4.5 hours and the ionic liquid could be recycled 8 times without significant loss of quality and reduction in catalytic activity. Proposed mechanism was given. Infrared data comparison and Gaussian 03 software simulation were used to confirm the reaction mechanism. The catalytic system owned the advantages of short reaction time, high product yield and recycled catalyst, providing a green surrogate for aza-Michael addition.Research shows that the designed and synthesized ionic liquids in this paper exhibit high catalytic activity in the studied reactions. The more widespread applications of the ionic liquids in other reactions can be further studied.