One-pot four-step direct synthesis of 2,5-furandicarboxylic acid from 2,5-diformylfuran under oxygen-free conditions

2,5-Furanedicarboxylic acid (FDCA) is a valuable compound with the potential as a renewable and green alternative to terephthalic acid in polyester production. To address the issues of flammability, explosiveness, and product separation challenges associated with the current aerobic oxidation of 5-hydroxymethylfurfural (5-HMF) to FDCA route, herein, for the first time, a one-pot four-step direct reaction pathway for the synthesis of FDCA from 2,5-diformylfuran (DFF) and hydroxylamine salt is proposed. Under optimized conditions of 120 degree celsius for 8 h, [HSO3-b-mim]center dot CF3SO3 catalyst and p-xylene-water dual liquid phase solvent, 100 % DFF conversion and 91.0 % FDCA separation yield were obtained. Notably, [HSO3-b-mim]center dot CF3SO3 exhibited excellent stability, maintaining its activity after being recycled more than five times. Through online experimentation and density functional theory (DFT) calculations, a four-step reaction mechanism involving aldehyde oximation, oxime dehydration, nitrile hydrolysis, and amide hydrolysis was proposed. This reaction pathway offers significant industrial application value due to its high FDCA yield, simple product separation, easy recovery and recycling of ionic liquid, and elimination of the need for oxygen.