Catalytic Dehalogenation Of Aryl Halides In Water By Metal N-heterocyclic Carbine Catalyst

In this paper, catalytic dehalogenation of aromatic halides with metal N-heterocyclic carbine (NHC) complexes in water was studied. The study showed that the catalytic reductive reaction can be happened under mild-conditions, normal atmosphere,60-80℃, aqueous phase, and with a water soluble hydrogen donor (hydrazine hydrate) regarded as the reducing agent. The product of this kind of reaction is single.1.Heterogeneous metal complex catalyst, Pd(Ⅱ)-NHC-SBA-15, was synthesized in four-component reactions among N-methylimidazole, Pd(OAc)2,(3-chloro-propyl) triethoxysilane and SBA-15. The product of each step was detected by1H-NMR,13C-NMR, organic elemental analysis and FTIR. The catalyst was characterized by SEM and N2adsorption-desorption. The Palladium in the catalyst was detected by ICP.2. The effect of aryl halides molecular structure on catalytic reductive reaction was discussed. The experimental results showed that the activity of aryl halides in the reaction was related with the molecular structure parameters, such as carbon-halogen bond energy and the steric factor etc., and the steric factors of substituent were the main factors especially. It is benefit to make the benzene activated and the halogen removed easily that not only the electron cloud on the halogen bia was attracted but also the electron density on the benzene was decreased by electron withdrawing group on the benzene. For the electron donating groups, on the contrary, the electron density on the benzene was increased and the inductive effect of halogen’s electronic absorption was promoted, so that the benzene was passivated against the removal of the halogen.3.Heterogeneous metal complex catalyst, Cu(I)-NHC-SBA-15, was synthesized in four-component reactions among N-methylimidazole, Cul,(3-chloro-propyl) triethoxysilane and SBA-15. The product of each step was detected by1H-NMR,13C-NMR, organic elemental analysis and FTIR. The catalyst was characterized by SEM and N2adsorption-desorption. The copper in the catalyst was detected by ICP. The activity of catalyst was tested.4. The effects to catalytic debromination of1-Bromo-2,4-dimethoxybenzene in the water were studied via catalyst amount, reaction temperature and hydrazine hydrate amount. The optimal reaction conditions as follows, catalyst0.05g, hydrazine hydrate2mL and reaction temperature of80℃, were obtained via the orthogonal and single factor experiments. The efficiency of catalytic debromination reached98.5%, and debromination effect is good.5. The reuse of the catalyst was studied, and the experimental results showed that the activity of the catalyst still remained after three times reused. The dynamics of the catalytic reaction was also studied. The results indicated that the catalytic debromination reaction was determined by the surface reaction, and the first order kinetics (Langmuir-Hinshelwood model) was followed. The possible mechanism of catalytic debromination was proposed addition-elimination.The innovations of this paper were proposed:(1)using the transition metal copper instead of precious metal palladium could reduce the cost of the catalyst,(2)heterogeneous catalyst, Cu(Ⅰ)-NHC-SBA-15, was synthesized and applied firstly to catalytic dehalogenation of aryl halides in the aqueous phase,(3)the reaction conditions were mild, and the productivity was good.