Dual-Anion-Rich Polymeric Ionic Liquid for the Conversion of Carbon Dioxide, Ethylene Oxide, and Aniline to 3-Phenyl-2-Oxazolidinone

The one-pot synthesis of 3-aryl-2-oxazolidinone from carbon dioxide (CO2), epoxides, and aniline represents a promising strategy for CO2 utilization. However, the efficiency remains far from adequate for industrial deployment, primarily due to the absence of purpose-designed catalysts. Herein, a dual-anion-rich (Br– and OAc–) polymeric ionic liquid (P-TBTOD-1/1/2) was synthesized via copolymerization of vinyl-functionalized ionic liquids (ILs), 1,1,3,3-tetramethylguanidine bromide ([AlTMG]Br), and 1,1,3,3-tetramethylguanidine acetate ([AlTMG]OAc), with divinylbenzene (DVB). The catalytic performance was evaluated for the synthesis of 3-phenyl-2-oxazolidinone from CO2, ethylene oxide (EO), and aniline in a batch autoclave at 2.5 MPa and 110 °C with a catalyst dosage of 4 wt % (based on aniline) for 1.0 h. The aniline conversion was 100%, and the yield of 3-phenyl-2-oxazolidinone was 75%. While Br– could effectively promote the cyclization reaction between CO2 and EO to form ethylene carbonate (EC), its catalytic efficiency in the subsequent conversion of 2-(phenylamino)ethanol and EC to 3-phenyl-2-oxazolidinone was limited. In contrast, OAc– exhibited significantly superior catalytic performance in this reaction. OAc– effectively activated aniline and EO to generate 2-(phenylamino)ethanol. The accumulation of 2-(phenylamino)ethanol and EC in the reaction system synergistically drove the equilibrium toward product formation, thereby significantly enhancing the overall yield of 3-phenyl-2-oxazolidinone. Additionally, P-TBTOD-1/1/2 exhibited outstanding stability, maintaining the yield of 3-phenyl-2-oxazolidinone almost unchanged after five consecutive runs. These findings indicate that P-TBTOD-1/1/2 is a promising candidate catalyst for CO2 utilization.