Iron(III) Sulfate-Mediated Synthesis of 2,5-Furandicarboxylic Acid Dimethyl Ester from Galactaric Acid

2,5-furandicarboxylic acid (FDCA) is one of the most studied bio-based monomers, being considered the best substitute for fossil-derived terephthalic acid in plastic production. FDCA is employed in the preparation of polyethylene furanoate (PEF), demonstrating superior mechanical and thermal proprieties compared to the widely used polyethylene terephthalate (PET). Nevertheless, FDCA synthesis mostly relies on the oxidation of the bio-based platform chemical hydroxymethyl furfural (HMF), whose notoriously instable nature renders FDCA yield and industrial scale-up production complicated. On the contrary, FDCA esters are less studied, even though they have greater solubility in organic media, which would favor their isolation and potential application as monomers for PEF. On these premises, we report herein an alternative green synthetic approach to FDCA methyl ester (FDME) using galactaric acid as the substrate, dimethyl carbonate (DMC) as the green media, and Fe2(SO4)3 as the heterogeneous Lewis acid. Optimization of the reaction conditions allowed the selective production of FDME in a 70% isolated yield; product purification was achieved via flash column chromatography over silica. Furthermore, it was possible to employ up to 5.0 g of galactaric acid in a single reaction, leading to a good isolated yield of FDME.