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.