Adipic Acid Production via Metal-Free Selective Hydrogenolysis of Biomass-Derived Tetrahydrofuran-2,5-Dicarboxylic Acid

Biomass-derived furans offer sustainable routes to adipic acid (AA), a key chemical in Nylon-6,6 synthesis. In this work, we show that tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) is a viable precursor for AA production, achieving up to 89% yield in a metal-free system containing HI and molecular H-2 in a propionic acid solvent at 160 degrees C. Reactivity studies demonstrate that the interplay between HI, H-2, and the solvent is essential for effective THFDCA ring opening. By measuring the reaction orders of HI and molecular H-2 and calculating an acid-base equilibrium constant in a nonaqueous solvent, we show that HI plays a multifaceted role in the reaction by acting both as a proton source and an iodide source to selectively cleave C-O bonds without overhydrogenation of carboxylic acid groups. Using reactivity studies, kinetic measurements, and first-principles computational insights, we demonstrate that metal-free activation of molecular H-2 plays a key role in the reaction, following HI mediated cleavage of the etheric C-O bond in THFDCA.