卟啉锰络合物对苯乙烯催化环氧化的研究

PORPHYRINATO MANGANESE COMPLEX CATALYZED STYRENE EPOXIDATION

本文研究了四苯基卟啉锰在次氯酸钠体系中对苯乙烯催化环氧化的性能,用原位可见光谱考察了环氧化反应过程,观察到络合物与氧的作用情况,阐明了卟啉锰一次氯酸钠体系对苯乙烯催化环氧化的机理。

Catalytic epoxidation of styrene by manganito-tetraphenylporphy-rin has been studied with sodium hypochloride as single oxygen donor. Many factors influencing the epoxidation reaction were investigated, such as: catalyst, phase transfer catalyst, solvent, axial ligand and the addition method of single oxygen donor. Five solvents were used. Experimental results show that CC14 and C2H4Cl2 are better than the others, their reaction selectivity are above 80%. MnTPP( OAc ) and MnTPPCl catalysts have good activity. Phase transfer catalyst is necessary for this reaction system. The epoxidation reaction does not take place without phase transfer catalyst. Axial ligand can increase electron density of the central metal,this will promote the formation of the active species -Mn-. Some kinds of axial ligands ( DMF, EtOH and pyridine ) were investigated. Pyridine is the best one, it can shorten the reaction time from 5 h to 0.5 h. The addition method of NaOCl has significant influence on the oxidation result. It is prefer to divide the NaOCl into several portions and to add them gradually. The reaction was studied by in-situ UV-visible spectrophotometry, which showed the obvious interaction between Mn catalyst and single oxygen donor. When -Mn-3+ comes into contact with OCl-, the absorption peak changes from 470 nm to 429 nm immediately, and than shifted to 435nm which was maintained for a moment. After the addition of styrene the 435nm peak returned to 470 nm quickly.The manganese OXO complex -Mn5 +- active species(with the absorption peak of 435nm) is formed according to the following reactions: -Mn3+Mn-→ -Mn5+- The active species -Mn5+- epoxidizes the styrene and itself is recycled to -Mn3+-.