Qian Wei, Tan Xin, Su Qian, Cheng Weiguo, Xu Fei, Dong Li, Zhang Suojiang
Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Beijing Key Laboratory of Ionic Liquids Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, P.R. China.
School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, 19A Yuquan Road, Shijingshan District, Beijing, 100049, P.R. China.
ChemSusChem. 2019 Mar 21;12(6):1169-1178. doi: 10.1002/cssc.201802572. Epub 2019 Feb 15.
Green synthesis of high-molecular-weight isosorbide-based polycarbonate (PIC) with excellent properties is a tremendous challenge and is profoundly influenced by the precursor. Herein, an ecofriendly catalyst was employed to obtain the more reactive PIC precursor dicarboxymethyl isosorbide (DC) with 99.0 % selectivity through the transesterification reaction of isosorbide with dimethyl carbonate. This is the indispensable stage of a one-pot green synthesis of PIC, playing a critical role in giving an insight into the polymerization mechanism of polymer synthesis through the melt transesterification reaction. To this end, a series of 4-substituted phenolate ionic liquids (ILs) were developed as a new type of high-efficiency catalyst for this reaction. These homogeneous ILs exhibited outstanding catalytic performances. The DC selectivity increased gradually with decreasing IL basicity; among the ILs studied, trihexyl(tetradecyl)phosphonium 4-iodophenolate ([P ][4-I-Phen]) showed the highest catalytic activity. Additionally, according to the experimental results and DFT calculations, a plausible nucleophilic activation mechanism was proposed, which confirmed that the reaction is activated through the formation of H-bonds and electrostatic interactions with the IL catalyst. This strategy of tunable basicity and structure of anions in ILs affords an opportunity to develop other ILs for the transesterification reaction, thereby conveniently providing a variety of polymers through a green synthetic pathway.
绿色合成具有优异性能的高分子量异山梨醇基聚碳酸酯（PIC）是一项巨大挑战，且受到前驱体的深刻影响。在此，采用一种环境友好型催化剂，通过异山梨醇与碳酸二甲酯的酯交换反应，以99.0%的选择性获得反应活性更高的PIC前驱体二羧甲基异山梨醇（DC）。这是PIC一锅法绿色合成中不可或缺的阶段，对于深入了解通过熔融酯交换反应进行聚合物合成的聚合机理起着关键作用。为此，开发了一系列4-取代酚盐离子液体（ILs）作为该反应的新型高效催化剂。这些均相离子液体表现出优异的催化性能。DC的选择性随着离子液体碱性的降低而逐渐增加；在所研究的离子液体中，三己基（十四烷基）鏻4-碘酚盐（[P ][4-I-Phen]）表现出最高的催化活性。此外，根据实验结果和密度泛函理论计算，提出了一种合理的亲核活化机理，证实该反应是通过与离子液体催化剂形成氢键和静电相互作用而被活化的。这种调节离子液体碱性和阴离子结构的策略为开发用于酯交换反应的其他离子液体提供了机会，从而通过绿色合成途径方便地制备各种聚合物。
