Acidic Ionic Liquid Preparation, Modification And Catalytic 2-mn Transfer Alkylation Of Applications

2,6-Dimethylnaphthalene (2,6-DMN) is a key monomer in the synthesis of polyethylenenaphthalate (PEN). At present, the technology route of multi-step method using toluene or the xylene as starting material which has been industrialized is long and the production cost is high. Compared to the multistep synthetic process,the synthesis of 2,6-dimethylnaphthalene(2,6-DMN) by the transalkylation of 2-methylnaphthalene(2-MN) and 1,2,4,5-tetramethylbenzene(TeMB) is one of methods with excellent exploitation value and potentiality. But because the products are complex, the separation of the DMN isomers is troublesome.As a result, searching the high effective and environmental benign catalysts for highly synthesis of 2,6-DMN by the transalkylation is the key technology.In this paper, triethylamine hydrochlorine-aluminium hloride ionic liquids (Et₃NHCl-AlCl₃), 1-butyl-3-methylimidazolium chlorid chlorine-aluminate ionic liquids ([C4mim]Cl-AlCl₃), N-butylpyridinium chlorid chlorine-aluminate ionic liquids([C4Py]Cl-AlCl₃) were prepared, and the Et₃NHCl-AlCl₃(x=0.67) had been modified by adding organic additives, metal chlorides and passed over HCl. The forms of anion in ionic liquids were characterized by 27Al NMR, the acidic properties of ionic liquids were characterized by Py-IR and acetonitrile-IR, and the protonation degree of materials was determined by the UV spectrograph. The transalkylation of 2-MN and TeMB was performed in Et₃NHCl-AlCl₃ , meanwhile, the process conditions were optimized. At the same time, the cation structure of the above chlorine aluminate ionic liquids , the modified method of Et₃NHCl-AlCl₃ ionic liquid and its catalytic performance were studied. The results of 27Al NMR , Py-IR and acetonitrile-IR showed that the molar fraction of AlCl₃ determined the acidic properties and forms of inorganic anions species of ionic liquids, the acidity of ionic liquids increase with the content of anhydrous aluminum trichloride. Moreover, the acidity may be adjusted in certain extent by passing over HCl.Take Et₃NHCl-AlCl₃ as catalyst,the reaction temperature, dosage of ionic liquid , mole ratio of 1,2,4,5-tetramethylbenzene (TeMB) to 2-MN , reaction time and other factors on the results of transalkylation of 2-MN with TeMB were studied, the optimum reaction condition was obtained: the molar fraction of AlCl₃ is 0.67, amount of ionic liquid is 9 mmol, molar ratio of TeMB to 2-MN is 1, reaction temperature is 20℃and reaction time is 8 h; Under the optimum reaction conditions, 36.8% conversion of 2-MN, 84.3% selectivity of DMN , 62.3% selectivity of 2,6-DMN and ratio of 2,6-DMN to 2,7-DMN 3.4 were obtained.The modified method of Et₃NHCl-AlCl₃ ionic liquid by adding phenol , o-xylene , EDTA ,CuCl, ZnCl2 and other materials were studied. The results showed that the modified ionic liquids had little effect on the catalytic performance of transalkylation. When modified by HCl, the acidity of Et₃NHCl-AlCl₃ ionic liquid increased, the catalytic performance of Et₃NHCl-AlCl₃ ionic liquid and the selectivity of 2,6-DMN were increased substantially. Under the optimal reaction conditions: the reaction temperature is 20℃,the amount of ionic liquid is 9 mmol, the molar ratio of TeMB to 2-MN is 1, the reaction time is 3 h ,the solvent is cyclohexane; Under the optimum reaction conditions, 15.6% conversion of 2-MN and 100% selectivity of 2,6-DMN were obtained.