Study On Acylation Reaction Of Benzene And Phthalic Anhydride Catalyzed By [Emim]Br-2AlCl₃

2-Benzoylbenzoic acid(BBA)is an intermediate for the synthesis of anthraquinone by the phthalic anhydride method,and anthraquinone is an important chemical dye.Usually,AICl3 is used as a catalyst for the reaction of synthesizing BBA from benzene and phthalic anhydride,but there are some problems such as environmental pollution,corrosion of equipment,and non-recyclability.Hence,the study on the acylation reaction of benzene and phthalic anhydride to BBA catalyzed by[Emim]Br-2AlCl3 has a important theoretical and applied significance,as well as has a guiding significance for the catalytic reaction of aromatics and anhydride acylation in the chloroaluminate ionic liquids.Firstly,1-ethyl-3-methylimidazolium bromide([Emim]Br)was synthesized by N-methimidazole and bromoethane.The synthesis conditions of[Emim]Br were optimized by React IR TM IC-10.The results showed that the variable temperature process of N-methylimidazole and bromoethane first reaction at 40? to white solid and then at 80? was more beneficial to the synthesis of[Emim]Br.Under optimized conditions,the yield of[Emim]Br reached 98.1%.Based on the results of FT-IR,the mechanism of the synthesis of[Emim]Br was proposed as follows:at first N-methylimidazole reactions with bromoethane to a five-membered cycli transition state,and then the transition state transforms into[Emim]Br.In addition,The effect of reaction conditions on the acylation of benzene and phthalic anhydride catalyzed by[Emim]Br-2AlCl3 was investigated,and the suitable reaction conditions were obtained as follows:n([Emim]Br-2AlCl3)/n(PHA)=2,reaction time of 5h,reaction temperature of 50?,n(BEN)/n(PHA)=20.Under above condition,the yield of BBA was 93.53%.Secondly,[Emim]Br-2AlCl3 was immobilized using impregnating method and[Emim]Br-2AlCl3/SiO2 was used to catalyze the acylation of benzene and phthalic anhydride,and the reaction conditions were optimized.The optimized reaction conditions were as following:chloribenzene as a solvent,n(BEN)/n(PHA)=10,n([Emim]Br-2AlCl3)/n(PHA)=2,a reaction temperature 80? and a reaction time 5h.Under above conditions,the yield of o-benbzoylbenzoic reached 88.8%.The reusability of[Emim]Br-2AlCl3/SiO2 was studied,and the reason for the inactivation of[Emim]Br-2AlCl3/SiO2 was analyzed by means of chemical titration and FT-IR.The results show that the deactivation of[Emim]Br-2AlCl3/SiO2 is caused by the loss of the active component[Emim]Br-2ApCp3,and it can be restored to the level of the fresh catalyst by adding the active component.Finally,[Emim]Br-2AlCl3 was immobilized by covalent bonding method to prepare[Emim]Br-2AlCl3/SiO2,and the improved load method can effectively load[Emim]Br-2AlCl3 into the SiO2.The catalytic performance of[Emim]Br-2AlCl3/SiO2 to synthesis of BBA was investigated and the better reaction conditions were obtained:chlorobenzene as a solvent,n(BEN):n(PHA)=10:1,n([Emim]Br-2AlCl3):n(PHA)=3:1,reaction temperature of 75? and reaction time of 5h.Under the conditions,the yield of BBA was 78.51%.Reuse experiments of[Emim]Br-2AlCl3/SiO2 showed that the activity of[Emim]Br-2AlCl3/SiO2 was basically unchanged after repeated use of 4 times.In addition,FI-IR analysis showed that the acylation of benzene and phthalic anhydride catalyzed by[Emim]Br-2AlCl3/SiO2 follows acyl cation mechanism.