Synthesis Of Bis-imidazolium Ionic Liquid And Application On Friedel-Crafts Reaction

Ionic liquids,as a kind of green functional materials,are widely used in the fields of organic synthesis,biological science,electrochemistry,gel preparation,gas chromatography,and material preparation.Exploration of ionic liquids as a solvent or catalyst in organic synthesis has become a hot research topic.The Friedel-Crafts reaction is an effective way to build aromatic alkyl substituents and aryl ketones,and plays an important role in the field of organic synthesis.The traditional Friedel-Crafts reaction catalyst has some problems such as easy hydrolysis,many by-products,poor selectivity,corrosion equipment and environmental pollution.In order to adapt to the green chemistry idea,the green and efficient catalyst is the inevitable choice.Ionic liquids,as environmentally friendly functional materials,are naturally applied to the Friedel-Crafts reaction.At present,AlCl₃ type ionic liquids are widely studied,but this ionic liquids have not completely overcome the problem of hydrolytic deactivation.Therefore,it is necessary to design and synthesize ionic liquids with low sensitivity to air and water and with high stability.In this paper,six bis-imidazolium ionic liquids[Cn?mim?₂]?MY-Br?₂?MY=ZnCl₂,In Cl₃.n=3,6,9?were synthesized by two-step synthesis method.The structures were characterized by ¹H NMR and ¹³C NMR,and were confirmed as target ionic liquids.The physical properties?viscosity and conductivity?of the mixed binary systems of the above six bisimidazolium ionic liquids and solvents?water/acetonitrile?were investigated,and the effects of temperature and concentration on the mixed system were investigated.The properties of the mixed system of bis-imidazolium ionic liquids and solvents are as follows:temperature has an effect on the viscosity and conductivity of the mixed system.With the increase of temperature,the viscosity of the mixed system gradually decreases,and the conductivity gradually increases.When at a certain temperature,with the increase of concentration,the viscosity of the mixed system increased gradually,the conductivity will also increase gradually.Under a certain concentration,the conductivity reaches the maximum and then decreases,and the whole is changed in the form of a wave.Acetonitrile was used as a probe molecule to quantitatively analyze the acidity of the bisimidazole ionic liquid by infrared spectroscopy.The results show that the acidity of the six ionic liquids is stronger than that of the metal chloride,and the acidity of the indium chloride type bisimidazole ionic liquid is stronger than that of the zinc chloride type bisimidazole ionic liquid.;when the anions are the same,the cations are the bis-imidazolium ion liquid[C₉?mim?₂]?InCl₃-Br?₂ with the longest substituent carbon chain has the strongest acidity,and was selected for the Friedel-Crafts reaction of aromatic hydrocarbons with benzyl chloride and acid chlorides to evaluate their catalytic activity.In the Friedel Alkylation reaction of benzyl chloride and aromatics,we used the reaction of benzene and benzyl chloride as a template reaction with[C₉?mim?]₂?InCl₃-Br?₂ as catalyst.The influence of the amount of ionic liquid,reaction temperature and reaction time on the catalytic performance were investigated.After adding 0.1 mmol ionic liquid under 50 ^oC for 5 h,the yield of diphenylmethane was 84%.And a possible mechanism was speculated.In addition,the alkylation reaction ofbenzyl chloride with different aromatic hydrocarbons was studied,and the corresponding target products were obtained.The results shows that aromatic hydrocarbons with an electron-donating group were attached to the benzene ring,and the yield of the corresponding product was higher.The[C₉?mim?]₂?InCl₃-Br?₂ catalyst was used for Friedel acylation of acyl chloride and aromatic hydrocarbons.Benzene with benzoyl chloride were used as the model reactions.The effects of the amount of ionic liquid,reaction temperature and time for this reaction were studied.After adding 0.1 mmol ionic liquid under 80 ^oC for 6 h,the yield of benzophenone reached 90%.And speculated that the possible reaction mechanism of benzene and benzoyl chloride in the synthesis of benzophenone catalyzed by ionic liquid.In addition,acylation reactions of different aromatic hydrocarbons with acyl chlorides were also studied and the corresponding aryl ketones were obtained.The results show that when the electron-donating group is attached to the benzene ring,the yield of the corresponding aryl ketone will be higher,which is consistent with the above-mentioned electron-effect rule of the alkylation reaction.In summary,ionic liquids have higher yields,better selectivity and fewer side reactions in reaction of Friedel Acylation.So bis-imidazolium ionic liquids are more suitable for Friedel Acylation reactions.