Ionic liquid is also known as room temperature ionic liquid, room temperature molten salt or organic ionic liquid and others. In general, ionic liquids are composed of organic cations and inorganic anions. In addition, most ionic liquids are liquid state at or near room temperature and have some degree of stability in water. Ionic liquids have the characteristics of tasteless, non-combustion, volatilization and easy recovery, so it is a good substitute for traditional organic solvents. In addition, compared with conventional solvents, ionic liquids have unique advantages in thermal stability and electrical conductivity. Moreover, by grafting different functional groups on ionic liquids, the properties of ionic liquids can be regulated to meet different needs. DABCO is an important class of organic bases, ionic liquids designed with which as a primary raw material are called DABCO-based ionic liquids. The general structure of DABCO-based ionic liquid is shown in Figure 1.
Figure 1. The general structure of DABCO-based ionic liquid.
DABCO-based ionic liquids are mainly used in some chemical reactions or in the preparation of certain substances.
- Michael addition reaction: Michael addition reaction is an important reaction to generate C-C bond, C-S bond and C-N bond, the products can be used in the synthesis of printing and dyeing auxiliaries, pharmaceuticals, pesticides, spices and others. Therefore, the study of Michael addition reaction has very important theoretical value and application prospect. DABCO-based ionic liquid, as a new green solvent, has been used in Michael addition reaction, and is a new method of Michael addition reaction. A new ionic liquid [DABCO-PDO] [BF] catalyst was prepared by a two-step method using DABCO as raw material. The catalyst was used to catalyze the Michael addition reaction between cycloimides and acrylates, acrylonitrile or β-unsaturated alkenes, and the yield of the product was more than 85%. Furthermore, the catalytic activity of the catalyst remained 82% after six cycles.
- Knoevenagel condensation reaction: Knoevenagel condensation reaction is an important method to form carbon-carbon double bond by dehydration condensation of carbonyl compound and active methylene compound, which is widely used in the fine chemical industry. However, the use of traditional organic solvents in the reaction process has the disadvantages of long reaction time, harsh reaction conditions and excessive amount of catalyst. In addition, most catalysts cannot be reused. However, DABCO-based ionic liquid can be used as a catalyst for Knoevenagel condensation reaction, which has the advantages of reusability, fast reaction rate, high yield and simple post-treatment, Therefore, this method has a good potential for industrial amplification.
Figure 2. An example of DABCO-based ionic liquid used in Knoevenagel condensation reaction.
- Others: In addition to the above applications, DABCO-based ionic liquids can also be used in the Baylis-Hillman reaction, the preparation of biodiesel and others. Moreover, DABCO-based ionic liquids show a good catalytic effect in the Baylis-Hillman reaction, which effectively promoted the reaction process and shortened the reaction time.
- Dan M, Qiao Y, Wang X, et al. DABCO-catalyzed Knoevenagel condensation of aldehydes with ethyl cyanoacetate using hydroxy ionic liquid as a promoter[J]. RSC Advances, 2018, 8(53):30180-30185.