Study On Microwave - Assisted Heterogeneous Catalysts For Green Organic Synthesis

Microwave-assisted heating is a hot topic in the field of chemistry in recent years, microwave heating can greatly shorten the organic reaction time and increase the selectivity of product, which is also in line with the basic principles of green chemistry from the view of energy saving. And when using microwave heating, we can choose a more difficult reaction, and more inexpensive substrate instead of a variety of expensive substrates, greatly reducing the cost of synthesis, to medicinal chemistry and agricultural chemicals, which are of great significance.Based on the accumulation of knowledge and literature of the preliminary work of study, we investigated the characteristics of microwave heating, and using microwave selective heating characteristics, designing a heterogeneous catalyst that is suitable for microwave heating, such change makes the catalytic activity of the catalyst under microwave conditions far higher than traditional heating methods. In addition, synthetic materials under microwave heating often have a pleasant surprise, we synthesized a new type of controllable ordered mesoporous material with a curved channel structure under microwave heating. The mesoporous material has large surface area and ordered pore structure, when used in catalytic reactions, it can adsorb substrate and then facilitating the contacts between the substrate. And ordered mesoporous materials are high stability, convenient synthetic, is also a new and widespread focued kind of material in recent years.Contents of this paper is divided into three parts:1.Prepare graphene oxide by redox method, and then mix with palladium acetate, after reduction we make the catalyst material that palladium nanoparticles immobilized on graphene(Pd/graphene), the palladium particles are about 2 nm and well distributed. Apply the catalyst into carbon-carbon cross-coupling Ullmann reactions of the wide source and inexpensive chlorobenzene. Under microwave irradiation, since graphene is a microwave absorbing carrier, the temperature of palladium/graphene is much higher than the temperature of the entire system, greatly improve its catalytic activity. The results show that after microwave heating for 2 h, the yield reaches 93.5%, higher than the use of homogeneous catalysts palladium acetate, and compared to the general oil bath heating for 20 h, 85.6% yield, we can see great advantage. In a series of substrates expansions of Ullmann reactions and Suzuki reactions still show excellent catalytic activity, proving the catalyst of good universality.And after reused the catalyst for 5 times, the catalytic activity can still be maintained.2. Use the as synthesis palladium/graphene catalyst mentioned in part 1 in losartan biphenyl drugs or BASF’s newest Xemium pesticide intermediates and try the reduction reactions of nitrobenzene. We choose chlorobenzene instead of the expensive bromine-containing substrate, which the price is less than a tenth of the original a substituted, modulate the reaction conditions and get a 90% yield, greatly reducing the cost of synthesis which is of great significance. And in gram-stage reactions, we can still reach a yield of 85%, indicating that the expansion of the amount of the reaction production is feasible. In nitro reduction reactions, we use ammonium formate instead of hydrogen as a reducing agent, we get a nearly 100% isolated yield under mild conditions.3. Prepare a new type of phenolic resin material with a curved and controllable channel under microwave heating. Through its synthesis conditions modulation, we find that with the changing of phenol concentration, the material structure changes from a two-dimensional hexagonal straight tunnel to a cubic curved tunnel, and we study the synthesis mechanism and growth process. After the material is sulfonated by chlorosulfonic acid, we get a solid acid catalyst, applied in the Prins reaction to get 1,3-dioxane derivatives. As the phenol resin is a hydrophobic catalyst, we use water as the reaction solvent instead of organic solvent, adsorbing reaction substrate and contacted sufficiently, compared with those reactions using organic solvents in the literature, still achieve very good yield of 92 %, realizing the aqueous medium organic synthesis.