半纤维素在离子液体中的乙酰化改性

本研究旨在验证工业富木聚糖半纤维素（溶解浆工艺的副产品），在1-乙基-3-甲基咪唑铵离子液体(EmimAc)和二氯乙酰氯(Cl2AcCl)体系中轻度乙酰化制备了水溶性半纤维素。用红外光谱和核磁共振光谱对乙酰化半纤维素的结构进行了表征。所得到的修饰产物可以完全溶解在水中，取代度(DS)在0.17~0.37之间。结构表征表明，其脱氢化的半纤维素主要由（1→4）连接的β-D-Xylp主链和羟基或-COCH3连接的Xylp单元的O-2和O-3组成。此外，轻度乙酰化为一锅化，半纤维素与EmimAc和cl2AcCl之间产生的混合酐反应，而不是Cl2AcCl。流变学行为测量结果表明，乙酰化的半纤维素溶液比参考的半纤维素具有剪切变薄行为，粘度较低。工业半纤维素优异的水溶性将扩大其应用领域，并更容易转化为所需的化学品。

This study aimed to verify that industrial xylan-rich hemicelluloses, a byproduct of the dissolving pulp production process, could be mildly acetylated in a system containing 1-ethyl-3-methylimidazolium acetate (EmimAc) and dichloroacetyl chloride (Cl₂AcCl) to prepare water-soluble hemicelluloses. The structure of the acetylated hemicelluloses was characterized via Fourier-transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The resulting modified products were completely soluble in water, with a degree of substitution (DS) ranging from 0.17 to 0.37. Structural characterization revealed that the acetylated hemicelluloses mainly consist of a (1→4)-linked β-D-xylopyranosyl (β-D-Xylp) backbone, with hydroxyl groups or acetyl (-COCH₃) groups attached to the O-2 and O-3 positions of the Xylp units. Additionally, the mild acetylation was a one-pot reaction, wherein the hemicelluloses reacted with the mixed anhydride generated in situ between EmimAc and Cl₂AcCl, rather than directly with Cl₂AcCl. Rheological property measurements showed that the acetylated hemicelluloses solutions exhibited shear-thinning behavior and lower viscosity compared to the unmodified reference hemicelluloses. The excellent water solubility of this industrial-grade hemicelluloses will broaden their application fields and facilitate their conversion into desired chemical products.