One-Pot Method for the Synthesis of 2,5-Furandicarboxylic Acid from Fructose: In Situ Oxidation of 5-Hydroxymethylfurfural and 5-Acetoxymethylfurfural over Co/Mn/Br Catalysts in Acetic Acid

2,5-Furandicarboxylic acid (FDCA) derived from biomass is a versatile platform chemical for producing various degradable polymers, especially polyethylene 2,5-furandicarboxylate (PEF). To reduce the high cost of feedstock, fructose instead of expensive 5-hydroxymethylfurfural (HMF) was used as the feedstock for producing FDCA in the acetic acid (HOAc) solvent by a one-pot, two-step method. Fructose was first catalytically converted into HMF and 5-acetoxymethylfurfural (AMF) in HOAc over the Amberlyst-15 catalyst. After the separation of only Amberlyst-15, the in situ-formed HMF and AMF were further catalytically oxidized to FDCA by air (oxygen) over homogeneous Co/Mn/Br catalysts following the free-radical chain reaction mechanism. HOAc was not only used as the solvent for the dehydration and following oxidation process but also served as the effective co-catalyst for the dehydration of fructose. The effects of catalyst species, dosage, and reaction temperature on the dehydration process and oxidation temperature on FDCA yield and purity were evaluated systematically. Under the optimized reaction conditions, a total yield of HMF and AMF of 50% and a final FDCA yield of 35% were achieved. Combined with experimental results and theoretical calculation, the reaction mechanism for fructose dehydration side reactions and the HMF and AMF oxidation reactions was proposed correspondingly. The proposed two-step, one-pot method using fructose as the starting material is a promising route for the commercial production of FDCA with the simple operation and viable yield.