Study On Microwave Assisted Aza-Michael Reactions Of Aromatic Amines And Acrylates And The Nonthermal Microwave Effects In Chemical Reactions

The microwave technology is widely used in organic synthesis. In a number of the published papers, microwave heating has been shown to dramatically reduce the reaction time, increase the yields, enhance the purity of the product by reducing unwanted side reactions compared to conventional heating methods, and simplely the experimental operation. The genuine reason of microwave promoting the reaction is a controversial issue. The subject of"nonthermal microwave effects"is the focus of the debates in scientific community.In this paper, the microwave assisted synthesis method was applied and the effect of microwave in organic reaction was debated.The three main sections of this thesis are as below:In the first part, the experiment studied on the comparison of microwave irradiation and conventional heating for the aza-Michael reactions of aromatic amines with acrylates. Under the same experimental conditions, the reaction yield under two methods were close, the difference between them was only 5-15%. There was no obvious difference on reaction rate constants by the two methods and the ratio of the reaction rate constant was between 1.089-1.386. The reaction rate of the aza-Michael reaction between 2-methylaniline and acrylate was the slowest, but the reaction rate constants ratio between microwave irradiation and conventional heating was the largest. The microwave effect was obvious in slow reactions. The reaction rate constant ratio between two methods was higher in temperature of 60℃than 70℃. Maybe low temperature was beneficial to observe the microwave effect. In this experiment no the nonthermal microwave effects had been founded.The second part was on the basis of the previous work. The simultaneous cooling technique was used to investigate the relationship between the microwave irradiation power and the reaction results. Microwave irradiation with simultaneous cooling reaction, microwave reaction and conventional heating reaction have been done. In the experimental process of microwave irradiation with simultaneous cooling reaction, the lowest average temperature and highest reaction temperature have been used, but got the higher reaction yield than other reactions. There ware some connections between microwave irradiation power and the reaction yield. In the experiment of microwave irradiation with simultaneous cooling indicated that no the nonthermal microwave effects exist. The last part was based on the solvent effect under the microwave irradiation reaction. In five types of solvents, the benzimidazoles can be gained by the reaction of 2-phenylenediamine and 4-methyl benzaldehyde. The reaction results were different in each solvent. The dielectric loss, boiling point and the efficiency of protonation were combined action on the reaction results. In the process of synthesis monosubstituted benzimidazoles, there was an important oxidation step. The efficiency of protonation of the solvents influenced the production of disubstituted benzimidazoles obviously.