Study On The Knoevenagel Reaction Under Electromagnetic Radiation

Since 1990s, as a rising interdisciplinary, microwave chemistry has undergone significant progress. Microwave assisted organic synthesis (MAOS) has become one of the most important branches and microwave radiation has found its use in nearly all of the ordinary types of organic reactions. The reactions in microwave field tend to be superior to usual by increased rates of reaction, higher yields, less side products and so on. Owing to the complexity of the interaction between microwave field and reaction systems, there has been controversy in the academic world about the reason why microwave advantages appear. The controversy focuses on whether microwave"non-thermal"effect exists.This paper is mainly consisting of three parts. In the first part, without any additional catalyst, the Knoevenagel condensation reactions between aromatic aldehydes and ethyl cyanoacetate were implemented with DMF used as solvent under microwave radiation heating and conventional oil bath heating, respectively. While the reaction temperature and time were kept the same, products'concentration standard curve was established and the reaction yields at each time point under two different heating modes were compared with assistance of HPLC. The results showed that yields under microwave heating were a bit higher than conventional heating. However, rigorously speaking, the difference can not be absolutely attributed to non-thermal effect of microwave.In the second part, within closed vessel under microwave radiation, the esterification of 2,4,6-trimethyl benzoic acid and five alcohols(methanol, ethanol, isopropanol, sec-butyl alcohol and cyclohexanol) were performed. A series of aromatic esters were prepared and the products'structures were identified by 1HNMR and IR spectrum.Infrared ray is also a kind of electromagnetic wave, which can enhance the vibration between atoms in the molecule or the rotation of molecule as a whole according to the energy matching principle, resulting in the transition of vibration energy levels and rotation energy levels. In the third part in this paper, the influence of infrared radiation to the organic reactions was preliminary discussed. Four reactions systems were chose as objects of investigation, which contain the condensation of benzaldehyde to benzoin under catalysis of vitamin B1, the aza-Michael condensation of o-methyl aniline and butyl acrylate, the condensation of ortho-aminoacetophenone and benzoyl hydrazine generating acetophenone hydyne, the esterification of benzoic acid and butanol. The comparison between infrared heating and conventional heating was performed. The results indicate that infrared radiation can not promote the reaction compared to conventional heating by oil bath.