Two-step synthesis of renewable glutaric acid from furfural over solid copper based catalysts

Glutaric acid, a C 5 dicarboxylic acid, servers as an essential monomer in nylon industry. Currently, it is primarily obtained as a byproduct of adipic acid production. Green synthesis of glutaric acid from bio-resources remains a grand challenge. Here, we present a two-step synthesis of glutaric acid from furfural via cyclopentanone as the key intermediate. In the first step, a series of Ni modified CuO x catalysts derived from HKUST-1 (Cu) displays a record conversion rate (20.8 h −1 at 140 ℃) in converting furfural to cyclopentanone, with 99.8 % conversion of furfural and 87.4 % selectivity to cyclopentanone. The d-d orbital coupling between Ni and Cu through the oxygen bridge bond leads to an upshifted d band center of Cu sites, inducing the σ-bonding between the e g orbital of the electron-deficient Cu 2+ and C=O bond of furfural. In the second step, the C=O bond of cyclopentanone can be activated effectively over electron-rich Cu 2+ sites of HKUST-1 (Cu). The oxidation of cyclopentanone to glutaric acid was achieved on heterogeneous catalyst for the first time, with 40 % and 17.6 % yield of glutaric and succinic acids, respectively. The reaction mechanism has also been proposed. DFT calculation has revealed that 1,1,2-trihydroxy-cyclopentane is an important intermediate product, with proton removal to form C-O· radical as the rate-determining step. This work provides insights into the synthesis of bio-glutaric acid through a chemocatalytic route.