Research On Microwave-promoted Halogen-exchange Reaction

Halogen-exchange fluorination is the main and efficient method to synthesis fluorinated aromatics. Nevertheless, the traditional halogen-exchange fluorination needs long time and inevitably companies with serious by-reactions. So, microwave was applied to promote greatly the reaction rate for about 50 times and also inhibit by-reactions. This dissertation is involved in systematical study of the effects and mechanism of microwave by some factors of heat resources, fluorinating agents, solvents, catalysts, by-products and kinetics, etc.Reaction-oriented special microwave equipment had been designed and manufactured. The application results from fluorination showed that the reaction rate increased with the following sequence: continuous full-wave commutation>continuous half-wave commutation>domestic-used intermittent half-wave commutation>common oil bath. Two anhydrous KF prepared by azeotropy and microwave drying both had much bigger specific surface area than by common calcinations. In which the latter was prepared by a creative method, being utilized expansion effect of extremely rapid heating by microwave. The studying outcomes of solvents showed that dimethyl sulfide (DMSO) was the best solvent fit for both microwave and traditional reaction because of its big polarity, high boiling point and stability. Investigation of catalysts indicated that common quaternary ammonium salts are easy to decompose under the rigorous reaction conditions though are effective as phase-transfer catalysts, while PEG-6000 had better stability but unfortunately worse phase-transfer catalytic performance. So a polymer called polydiallyldimethylammonium chloride was synthesized to possess the advantages of the above two. In addition, Lewis acids AlCl3 and SbCl3 were used to catalyze fluorination under common pressure and an "ortho-effect" was found to be present in the fluorination of a series of chloronitrobenzenes because it promoted the yield and reaction rate of ortho-group-contained fluorinations much higher than that of non-ortho-group-conatined ones. Many by-products were detected in the reaction mixture and considered to be formed deriving from water, solvents and the reactants themselves.The kinetic research indicated that the traditional halogen-exchange fluorination was a first order reaction, and the reaction from original chloronitrobenzenes to corresponding fluoronitrobenzenes to arylmethylsulfide was a continuous reaction. Nevertheless, the microwave-promoted fluorination was obviously not a first order reaction yet, which was safe to take it for "non-heat effect" of microwave. And the theoretical discuss and experimental results also sustained this point.