Application Of A Biomimetic Heterogeneous Catalysis System To Knoevenagel Condensation

Knoevenagel condensation is one of the most important reaction for the formation of carbon-carbon double bond. The reaction products of Knoevenagel condensation, α,β-unsaturated carbonyl compounds, has played an significant role in synthesis of medical intermediates and the natural products intermediates. However, traditional Knoevenagel condensation costs large amounts of organic solvent with low yield. It is a tedious process for the separation and purification of reaction products. Meanwhile, the catalyst is difficult to recycle. Since the similar condensation reactions in plants have no such disadvantages, so inspired by the biomimetic catalysis, a biomimetic catalytic system for Knoevenagel condensation reaction was designed.In this paper, the benzaldehyde and diethyl malonate were selected as the reactants, which were distributed in the plants. Knoevenagel condensation between the two reactants was chosen as the probe to investigate the biomimetic catalytic system. The effects of different amine alkali groups in single-phase, two-phase and three-phase catalytic reactions and its synergy on biomimetic catalytic systems were thoroughly studied and the mechanism of biomimetic catalytic systems was discussed.Firstly, the factors affecting the stability of ester under the biomimetic conditions were thoroughly investigated by exploring the stability of ethyl acetate as the probe, such as optimum temperature, p H and reaction time. At the same time, the possible side reactions for the Knoevenagel condensation reaction between the benzaldehyde and diethyl malonate were studied, which provided references to determining the Knoevenagel condensation reaction conditions in the biomimetic environment. Secondly, in the homogenous reaction system, the effects of different types of amino alkali on the catalysis action and the synergistic action for the condensation reaction between the aromatic aldehyde and diethyl malonate were investigated. The results demonstrated that in the non-aqueous solvent, the condensation products of carbonyl groups could form an imine, which showed lower catalytic activity than the secondary amine. However, in the aqueous solvent, water could promote the separate of the amine and products, so the primary amines exhibit better catalytic activity than the secondary amine. Thus, biomimetic aqueous heterogeneous catalytic system was designed. The interaction between the different amino alkali and reactants including aromatic aldehyde and diethyl malonate was investigated. Besides, the synergy law in amine base- organic acids, and the synergies of different amino bases were also studied.The results indicated that the system has the following the features, mild reaction conditions, coupled reaction and separation and reusable ability. Our research has laid a good foundation for the following studied, and also provided useful reference for the explanation of enzyme catalysis. Thus, our research has certain academic significance.