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 H2 in a propionic acid solvent at 160 °C. Reactivity studies demonstrate that the interplay between HI, H2, and the solvent is essential for effective THFDCA ring opening. By measuring the reaction orders of HI and molecular H2 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 H2 plays a key role in the reaction, following HI-mediated cleavage of the etheric C–O bond in THFDCA.