Transesterfication of isosorbide with dimethyl carbonate catalyzed by task-specific ionic liquids.

Green synthesis of high-molecular-weight isosorbide-based polycarbonate (PIC) with excellent properties is a tremendous challenge, which is profoundly influenced by the precursor. Herein, we employed an eco-friendly catalyst to achieve the more reactive PIC precursor dicarboxymethyl isosorbide (DC) selectivity of 99.0% through the transesterfication reaction of isosorbide with dimethyl carbonate (DMC), which is the indispensable stage of one-pot green synthesis of PIC, playing a critical role in insight into the polymerization mechanism of polymers synthesis by melt transesterfication reaction. For this, 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 exhibit outstanding catalytic performance. The DC selectivity is gradually increasing with the decrease of basicity of ILs, among of which trihexyl(tetradecyl)phosphonium 4-iodophenolate ([P66614][4-I-Phen]) shows the highest catalytic activity. Additionally, according to the experiment and DFT calculations results, a plausible nucleophilic activation mechanism was put forward, which confirmed that the reaction was activated through formation of H-bond and electrostatic interactions with IL catalyst. This strategy of tunable basicity and structure of anions in ILs affords an opportunity to develop other ILs for transesterfication reaction, thereby conveniently providing a variety of polymers via a greener synthetic pathway.