Synthesis Of Aryl Ether By Environmentally Friendly Catalyst-Chitosan-Supported Palladium

Aryl ethers are important compounds, and there are also important applications in pesticides, pharmaceuticals, fragrances, dyestuffs and so on. Recently, more and more research has been focused on their synthesis. The Pd-catalyzed synthesis of aryl ethers has been reported, however, this catalytic process has many disadvantages, such as the multiple intermediate products, lower yield, difficult recovery of catalyst and high cost. Chitosan is the natural polymer containing -NH₂ and -OH groups, which can coordinate with metal ions well. Since the chitosan-supported noble metal catalysts have high stability, little causticity and low-solvents-solubility, all of which is easy to the separation, recovery and reuse of catalysts. The research and application of the natural polymer chitosan-supported palladium catalyst is paid attention in recent years.First of all, the survey of research on aryl ethers and supported palladium catalysts, and the recent advance in the study on the chitosan-supported palladium catalyst applications were reviewed in this paper. According to the investigation of reference, it shows that the palladium complexes used as catalysts to synthesize aryl ethers had been studied, but the chitosan-supported palladium complex for this catalyzed synthesis has not been reported.Secondly, Natural chitosan-supported palladium, modified chitosan with salicylad- ehyde palladium complex, and SiO₂ supported chitosan Schiff-base palladium catalys- ts were prepared by immersion method using chitosan and palladium chloride as raw material. These catalysts were characterized by FT-TR and NMR; the results showed that chitosan had coordinated with palladium well. At the same time, the synthesis method of 4-nitrodiphenyl ether was discussed. It is concluded that there is a relative reasonable route for this synthesis of 4-nitrodiphenyl: this reaction use p-nitrochlorob- enzene, phenol and sodium hydride as material, toluene as solvent, chitosan-supprted palladium as catalyst.Thirdly, the performance of chitosan-supported palladium catalyzed synthesis of diphenyl ethers was studied. An orthogonal test was designed; Effects of the molar ratio of materials, reaction temperature, reaction time and catalyst consumption on the yields were investigated. The results indicate that the optimal reaction conditions are: 1:1molar ratio of phenol and p-nitrochlorobenzene, 2:1molar ratio of sodium hydride and p-nitrochlorobenzene, 30mL toluene, 0.20g catalyst, 65℃for 9h under an atmos- phere of nitrogen. Under these conditions, the yield of 4-nitrodiphenyl is 79.0%. Similarly, under the optimal reaction conditions: 1.5:1molar ratio of phenol and p-nitrochlorobenzene, 2:1 molar ratio of sodium hydride and p-nitrochlorobenzene, 30 mL toluene, 0.20g catalyst, 100℃for 10h under an atmosphere of nitrogen, the yield of 4-phenoxyaniline is 78.4%. The catalyst has good activity and good repeatability, for it can be separated easily from the product with extraction, then reuse for many times.Finally, the chitosan-palladium complex catalysts on SiO₂ were prepared, and the catalytic performance of this catalyst in the synthesis reaction of alkyl aryl ethers was explored. The research reveals that this catalyst has good catalytic activity in the reac- tion, especially in the synthesis reaction of p-nitroanisole by using p-nitrochlorobenz- ene, methanol and sodium hydroxide as raw material, the reaction condition is also mild.In a word, these catalysts are easily prepared, separated from the reaction mixture, reclaimed and reused, meanwhile, they perform high activity for the synthesis of aryl ether.