Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, PR China.
State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, PR China.
Sci Rep. 2016 Sep 20;6:33725. doi: 10.1038/srep33725.
In the present study, we describe a novel one-step method to prepare water-soluble cellulose acetate (WSCA) with higher degree of polymerization values (DP = 650-680) by in situ activation of carboxyl group in ionic liquid. First of all, cellulose was dissolved in 1-ethyl-3-methylimidazolium acetate (EmimAc) and reacted with dichloroacetyl chloride (Cl2AcCl) in order to make cellulose dichloroacetate. Under various conditions, a series of water soluble products were produced. Elemental analysis and NMR results confirmed that they were cellulose acetate with DS (degree of substitution) values in the range from 0.30 to 0.63. NMR studies demonstrated that Cl2AcCl reacted with acetate anion of EmimAc producing a mixed anhydride that acetylated cellulose. Other acylating reagents such as benzoyl chloride, chloroacetyl chloride can also work similarly. 2D NMR characterization suggested that 6-mono-O-acetyl moiety, 3,6-di-O-acetylcellulose and 2,6-di-O-acetyl cellulose were all synthesized and the reactivity of hydroxyl groups in anhydro-glucose units was in the order C-6>C-3>C-2. This work provides an alternative way to make WSCA, meanwhile, also services as a reminder that the activity of EmimAc toward carbohydrate as acylating reagents could be a problem, because the expected acylated products may not be resulted and recycling of this ionic liquid could also be difficult.
在本研究中，我们描述了一种通过离子液体中羧基原位活化来制备具有更高聚合度（DP=650-680）的水溶性醋酸纤维素（WSCA）的新一步法。首先，纤维素溶解在 1-乙基-3-甲基咪唑醋酸盐（EmimAc）中，并与二氯乙酰氯（Cl2AcCl）反应，以制备纤维素二氯醋酸酯。在各种条件下，生成了一系列水溶性产物。元素分析和 NMR 结果证实，它们是取代度（DS）值在 0.30 至 0.63 范围内的醋酸纤维素。NMR 研究表明，Cl2AcCl 与 EmimAc 的醋酸盐阴离子反应生成酰化纤维素的混合酸酐。其他酰化试剂，如苯甲酰氯、氯乙酰氯也可以类似地反应。2D NMR 表征表明，均合成了 6-单-O-乙酰基、3,6-二-O-乙酰纤维素和 2,6-二-O-乙酰纤维素，而且在无水葡萄糖单元中羟基的反应活性顺序为 C-6>C-3>C-2。这项工作提供了一种制备 WSCA 的替代方法，同时也提醒人们，EmimAc 作为酰化试剂对碳水化合物的活性可能是一个问题，因为预期的酰化产物可能不会产生，而且这种离子液体的回收也可能很困难。
