摘要
酸性离子液体具有催化活性高、选择性好、对设备腐蚀小、易于回收利用等优点,可代替浓硫酸合成乙酰丙酸酯。制备了8种酸性离子液体,其中阳离子分别是咪唑、吡啶、季铵盐类,阴离子分别是无机酸和有机酸类,利用1H NMR和13C NMR表征了离子液体结构,热重分析了各离子液体热稳定性,Hammett指示剂结合紫外光谱法比较了不同离子液体的Br9nsted酸性,并探讨了利用碳水化合物醇解的催化效应。结果表明,8种离子液体醇解催化反应中,[Bmim-SO3H]HSO4表现出最高的催化活性,且对乙酰丙酸乙酯(EL)有最高的选择性,各离子液体催化合成产物EL的活性与其Br9nsted酸性密切相关。利用此催化剂讨论反应底物、醇解温度、催化剂用量对合成EL的影响,结果表明,果糖具有最高的反应活性,以葡萄糖为底物,催化剂用量2 mmol,醇解温度170℃,时间60 min,EL的最高摩尔产率可达56. 79%,另外,催化剂重复利用5次仍保持较高的回收率和催化活性。说明[Bmim-SO3H]HSO4在催化碳水化合物醇解合成EL过程中结构性质稳定,表现出较优的催化转化效率。
Acidic ionic liquids(ILs)are used as promising and environmentally-friendly catalysts for levulinates synthesis,which can replace the sulfuric acid owing to their beneficial characteristics such as high catalytic activity,high selectivity,low corrosion of equipment and ease of recycling.Eight different acidic ILs were examined as catalysts in the synthesis of ethyl levulinate(EL)from carbohydrates with ethanol.Among them,the cations of ILs were imidazole,pyridine and triethylamine salts,and the anion ions were inorganic acids and organic acids.The structures of ILs were confirmed by 1 H NMR and 13 C NMR.All of the ILs exhibited excellent thermal stability over 200℃through the TG DTG.The acidity of the ILs was investigated by determining the Hammett acidity functions under UV-visible spectroscopy by using 4-nitroaniline as indicator.The introduction of a SO 3 H group into the IL greatly increased its Br nsted acidity.Anions of ILs had a great influence on the acidity of ionic liquids,and cations with imidazoles were more acidic than pyridine and triethylamine salts.It was found that the[Bmim-SO 3 H]HSO 4 showed the best catalytic activity among all the ILs.The activity of catalytic synthesis of EL was closely related to the Br nsted acid.The highest EL yield of 56.79%was obtained for the reaction carried out at 170℃for 60 min with 2 mmol[Bmim-SO 3 H]HSO 4 as catalyst and using glucose as the substrate.Furthermore,the ILs remained high activity and stability after reused for 5 times.On the whole,[Bmim-SO 3 H]HSO 4 had stable structural properties in the process of catalytic alcoholysis of carbohydrates into EL,showing a better catalytic conversion efficiency.
作者
刘欢
吕欢欢
赵婷婷
赵广路
韩鲁佳
肖卫华
LIU Huan;Lü Huanhuan;ZHAO Tingting;ZHAO Guanglu;HAN Lujia;XIAO Weihua(College of Engineering,China Agricultural University,Beijing 100083,China)
出处
《农业机械学报》
EI
CAS
CSCD
北大核心
2018年第11期289-297,共9页
Transactions of the Chinese Society for Agricultural Machinery
基金
国家重点研发计划项目(2016YFE0112800)
国家自然科学基金项目(31671572)
中央高校基本科研业务费专项资金项目(2018TC027)
关键词
乙酰丙酸乙酯
酸性离子液体
合成
催化醇解
ethyl levulinate
acidic ionic liquids
synthesis
catalytic alcoholysis
