Molecular Origin for the Difficulty in Separation of 5-Hydroxymethylfurfural from Imidazolium Based Ionic Liquids

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• 作者：Huiyong Wang ; Shuyan Liu ; Yuling Zhao ; Hucheng Zhang ; Jianji Wang
• 刊名：ACS Sustainable Chemistry & Engineering
• 出版年：2016
• 出版时间：December 5, 2016
• 年：2016
• 卷：4
• 期：12
• 页码：6712-6721
• 全文大小：580K
• ISSN：2168-0485

文摘

Ionic liquids (ILs) have shown superior performance in the conversion of biomass to 5-hydroxymethylfurfural (5-HMF) as reaction medium and/or catalyst, which is a green platform compound with a wide range of applications in manufacturing fine chemicals and biofuels. Nevertheless, the separation of 5-HMF from ILs is very difficult and becomes a technical bottleneck for IL application in the preparation of 5-HMF. To resolve this problem, understanding the interactions between ILs and 5-HMF is essential. In this work, attenuated total reflectance Fourier transform infrared, ¹H nuclear magnetic resonance, and quantum chemistry calculations were combined to investigate the interaction between 5-HMF and each of the eight ILs over the whole composition range. The studied ILs have the same 1-butyl-3-methylimidazolium cation [C₄mim]⁺ but different anions. It was found that interactions between the ILs and 5-HMF were mainly ascribed to the strong hydrogen bonds of 5-HMF with anions of the ILs, and the formation abilities of hydrogen bonds of the anions with O–H group of 5-HMF were found to decrease in the order [CH₃COO]⁻, [C₂H₅COO]⁻ > [HSO₄]⁻ > [CF₃COO]⁻ > [N(CN)₂]⁻ > [NO₃]⁻ > [CH₃OSO₃]⁻ > [BF₄]⁻. These results suggest that the anions with stronger hydrogen bond accepting ability have stronger interaction with 5-HMF and the separation of 5-HMF from the ILs is mainly governed by the hydrogen bonding interactions between anion of the ILs and 5-HMF. In addition, partition coefficients of 5-HMF between 1,4-dioxane and the ILs phases were determined experimentally to support the conclusion.