The Optimization Conditions And Mechanism Of Ullmann Coupling Reaction

The synthesis reaction of biphenyl compounds plays an important role in the filed of organic chemistry, because the products are the key components in construction of many natural substances, biological and chemical preparation, drug. Ullmann coupling reaction is a common reaction to compound biphenyl and has been researched deeply. From the initial copper homogeneous catalytic system to the palladium homogeneous/heterogeneous catalytic system and the efficient heterogeneous bimetallic catalytic system. However, there are some questions about the mechanism of Ullmann coupling reaction catalyzed by bimetallic catalyst, such as, the intermetallic interaction, the effect of solvent, base and catalyst in the reaction process.Bimetallic Pd-Au supported on Mg-Al hydrotalcite is a catalyst chosen to catalyze Ullmann coupling reaction of bromobenzene, then we got the optimization conditions and mechanism of Ullmann coupling reactionin in the following ways:(1) Magnesia-alumina hydrotalcite were synthesized by a coprecipitation-hydrothermal method. A series of bimetallic catalysts with different palladium-gold proportion were prepared by liquid phase reduction method and characterized by X-ray photoelectron spectroscopy(XPS), N2-adsorption/desorption, transmission electron microscopy(TEM) and X-ray diffraction(XRD) and so on.(2) The optimization conditions of reaction as follows: the ratio of palladium-gold, metal loading, catalyst quantity, base quantity and temperature were 1:3, 1wt %, 33 mg, 1.1 mmol and 30 ℃.(3) Base quantity, the effect of solvent, the reaction kinetics and characterizations of catalysts were studied to explore the mechanism of Ullmann coupling reaction. The results showed the relationship between the reduction of base and bromobenzene is 2:1 and acetone were consist of two parts in the Ullmann coupling reaction. One part comes from Ullmann coupling reaction and another comes from alcohol catalytic dehydrogenation and the relationship between these two types is 1:1. Designing experiments also showed that the relationship between the substrate conversions and the amount of acetone generated by isopropanol is 1:1.