Base-promoted O2 relay activation for the efficient HMF oxidation to FDCA at low temperature and ambient pressure

Base-regulated ROS strategy enables mild HMF-to-FDCA oxidation. • NaHCO 3 stabilizes ·O 2 − ; NaOH promotes ·O 2 − /·OH synergy. • NaOH system drives O 2 relay: O 2  → ·O 2 −  → H 2 O 2  → ·OH for FDCA synthesis. The sustainable conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) via aerobic oxidation is a cornerstone of future biorefinery, yet its practical implementation under mild conditions is constrained by the spin-forbidden activation of triplet O 2 . In this work, we report a base-regulated reactive oxygen species (ROS) strategy that enables efficient HMF oxidation to FDCA at low temperatures (30–60 °C) under ambient oxygen pressure. We find that weak base NaHCO 3 selectively stabilizes ·O 2 − , directing a selective oxidation pathway, whereas strong base NaOH promotes a synergistic ·O 2 − /·OH mechanism that substantially accelerates the overall reaction. Through careful optimization, a 95.8% FDCA yield is obtained under ambient O 2 flow. Kinetic analysis, including reaction order determination and kinetic isotope effect measurements, demonstrates that O 2 activation is the rate-limiting step in the NaOH system, following a relay activation pathway of O 2  → ·O 2 −  → H 2 O 2  → ·OH. This work not only elucidates the mechanistic role of bases in regulating ROS during HMF oxidation but also provides a practical and green route for synthesizing FDCA under mild, ambient-pressure conditions, advancing the field of sustainable biomass conversion. This work demonstrates a base-regulated reactive oxygen species (ROS) strategy for the mild oxidation of HMF to FDCA. The weak base NaHCO 3 selectively stabilizes ·O 2 − , directing a selective oxidation pathway, whereas the strong base NaOH promotes synergistic ·O 2 − /·OH participation, substantially accelerating the reaction. Mechanistic studies reveal that O 2 activation follows a relay pathway: O 2  → ·O 2 −  → H 2 O 2  → ·OH in the NaOH system. Under ambient oxygen pressure and at 30–60 °C, a 95.8% FDCA yield is achieved, offering a new route for green biomass conversion. Download: Download high-res image (47KB) Download: Download full-size image