One-step production of renewable adipic acid esters from mucic acid over an Ir–ReOx/C catalyst with low Ir loading

Abstract

The production of adipic acid, a large-volume platform chemical, from biomass represents a petroleum-free route to manufacturing nylon and other polymers more sustainably. In this study, a one-step conversion of bioderived mucic acid to adipates is reported over a heterogeneous, bifunctional Ir–ReO_x/C catalyst via deoxydehydration (DODH) and catalytic transfer hydrogenation (CTH) using isopropanol as a green solvent and reductant. With very low Ir content (0.05 wt%), the catalyst provides a low-cost option for the tandem DODH–CTH process, while still enabling reuse and regeneration for at least five cycles. The reported catalytic system generates adipates in good yield (63%) without the need for additives (acids or halogens) or high pressure H₂. Through model reactions and spectroscopic analyses, a bifunctional DODH–CTH mechanism was supported, with the Re^VI/IV redox pair as the active DODH species and Ir⁰ saturating the dialkene intermediate via CTH. Thermal treatment in catalyst preparation and regeneration was optimized to limit metal leaching while maintaining good activity. The present work outlines a one-step deoxygenation of an aldaric acid substrate from biomass using a bimetallic catalyst of low noble metal content to an important monomer for the polymer industry. This system facilitates use in future syntheses of sustainable chemicals from renewable oxygenates where the catalyst is reusable and affordable.