Tandem Catalysis Enables the Hydrocarboxylation of γ-Valerolactone with CO₂ and H₂ to Produce Adipic Acid

Adipic acid is an industrially important chemical that is currently produced from fossil resources. In this work, we report the first method for the production of adipic acid from biomass-derived γ-valerolactone (GVL) with CO₂ and H₂. It was discovered that the Rh catalyst with an I₂ promoter in a binary solvent system of AcOH/H₂O could catalyze the reaction efficiently at an industrially relevant temperature (140 °C). A systematic and detailed analysis of the reaction pathway was conducted via experimental and DFT studies. The tandem one-pot process permits thermodynamic leveraging by coupling the thermodynamically unfavored GVL ring-opening with highly favored hydrocarboxylation, driving the overall reaction forward to diacid products. The reaction involves three key steps, including the reduction of CO₂ to CO and H₂O by H₂, the ring-opening of GVL to reaction intermediates, and the hydrocarboxylation of the intermediates with CO and H₂O. The stable GVL can maintain a low concentration of the highly reactive intermediates and prevent their hydrogenation side reactions, which favors the high selectivity of diacids. Moreover, this strategy affords access to various diacids in high yields from different lactones, and the yield of the diacids could reach 89%. This protocol opens the way for the sustainable synthesis of adipic acid from two renewable carbon resources and a green reductant (H₂).