(576e) Cyclization and Dehydration of Aldaric Acids to 2,5-Furandicarboxylic Acid

Aldaric acids (2,3,4,5-tetrahydroxy-1,6-hexanedioic acids) are formed by catalytic oxidation of glucose or by oxidation of uronic acids, the monomers of pectin and alginate biopolymers. Aldaric acids are emerging as important biorenewable intermediates for use in consumer goods and as platforms for further conversion. The direct cyclization and dehydration of glucaric acid and galactaric acid and their esters to form 2,5-furandicarboxylic acid (FDCA) has been carried out. The production of FDCA is attracting a great deal of attention, as it is a monomer of polyethylenefurandicarboxylate (PEF) polymers, which exhibit superior barrier properties to PETE packaging materials. Aldaric acid cyclization to FDCA takes place in an anhydrous environment in the presence of strong acids; we have found that under some conditions the presence of an ionic liquid solvent (1-butyl-3-methylimidazolium with various anions) enhances the yield of FDCA. An optimized set of reagent compositions and reaction conditions have been identified to give FDCA yields approaching 60% of theoretical from galactaric acid. Undesired reaction pathways include lactonization of the aldaric acids under anhydrous conditions, and total dehydration to form carbonaceous residues. A method to recover pure FDCA directly from the reaction mixture has been developed, along with recycling of the ionic liquid and acids. This new route to FDCA avoids the use of difficult-to-handle intermediates such as hydroxymethylfurfural (HMF), and appears promising given the recent advancements in commercialization of the aldaric acid precursors.