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Study on Biginelli Reaction under Microwave-Assisted Hydrothermal Conditions

Author: CaoHuanQi
Tutor: LiuXiao
School: Jilin University
Course: Inorganic Chemistry
Keywords: Microwave radiation hydrothermal condition Biginelli reaction Raman spectrum
CLC: O621.25
Type: Master's thesis
Year: 2010
Downloads: 87
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Abstract

With the increasing global demand for environmental protection and resource conservation, more and more chemists have to face a sacred but pressing task to protect our mutual environment. Since in a conventional chemical reaction, many solvents must be wasted during the reaction as well as the post-processing, the development of a new and green experimental method to reduce solvents’use is particularly essential. As opposed to conventional heating methods, though the burner could increase the combustion efficiency, and high efficiency heating units have somehow cut back energy waste, there are still plenty of energy consumption in these two devices. Luckily enough, the emergence of microwave heating device pointed out us chemists a new and exciting direction - microwave assisted synthesis - the mainstream of heating devices in 21st century.Single-mode microwave-assisted organic synthesis reactor almost covers all of the green chemistry requirements, such as low power consumption, high yield, simple purification of products, short reaction time, wide range of solvents, and controllable generation of a specified product. For their wide and powerful medical applications, dihydropyrimidinones (DHPMs), as products of Biginelli reactions, are especially fundamental in biopharmaceutical industry. As I analysized above, we may easily see that synthesis of dihydropyrimidinones under single-mode microwave radiation by Biginelli reaction pathway is extremely crucial for synthesizers. Reactions under hydrothermal conditions could sometimes improve the yield or bring some wonderful phenomena as pressure and temperature continue to rise, especially when the change of activation volumes is highly minus. This not only stems from the reduction of the distance between molecules under high pressure, but also arises from the fact that many solvents will get into super-critical state under high pressure. So the research of high-pressure organic synthesis has become particularly noticeable.In recent years, with a wide development of surface-enhanced Raman technology, Raman spectrometer entered many laboratories again. Micro-Raman spectroscopy is playing a very important role in the fields of solid materials researches, surface chemistry and some other materials characterization fields. Raman spectroscopy has become the first choice of substances identification and in-situ materials characterization. This is not only because of its fast and easily remote operation, but also because it could penetrate the materials to detect the inner lays. What is more, similar but faster than a traditional surface analysis technology called Raman mapping, a new emerging technology named Raman Streamline Imaging Technology still needs much more attentions, so I talked about it in this thesis.Furthermore, in this dissertation, I used single-mode microwave radiation and high pressure hydrothermal technology to synthesize dihydropyrimidinones through a one-pot Biginelli reaction. I was trying to make breakthroughs in the following three areas: (1) to explore the possibility and feasibility of high-pressure hydrothermal synthesis of heterocyclic compounds, such as DHPMs (dihydropyrimidinones); (2) to realize the synthesis of heterocyclic compounds by single-mode microwave radiation, and also to try to make the reaction greener and more expeditious without much complicated purification of product; (3) trying to find a faster and more efficient product identification way.To realize the above objectives, I firstly employed a single-mode microwave reactor. I used acetic acid and alcohol as solvent, and finished the reaction in 10min. After a series of experiments, two kinds of dihydropyrimidinones were gotten and characterized, with yields up to 75%. At the same time, this thesis also discussed many frequent errors during microwave organic synthesis. In addition, I synthesized DHPMs, yield of 50%, in sealed brass tubes under 100MPa. This shows us a potential domain of hydrothermal organic synthesis. Finally, I employed Raman Streamline imaging technology to analyze the Biginelli reaction products. What enlightened me is that all the operations during one characterization could be finished within 30 min, including sample preparation, micro-region scanning, micro imaging, and regional analysis. This technology could reveal us the component contents on a small surface area of a mixture. Based on this rapid demonstration of compositions, further improvement of the efficiency of drug synthesis and non-destructive identifications of surface materials in a lot of basic research areas is possible.

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