Dehydrogenative Coupling of Ethanol to Ethyl Acetate in Compressed CO₂: An Acceptor-Less Approach

Acceptor-less dehydrogenative coupling represents a long-standing and critical challenge in the synthesis of valuable chemicals while also offering the potential for green hydrogen production. Herein, we demonstrated a highly selective method for the synthesis of ethyl acetate from ethanol without any need for additives or oxidants using heterogeneous Ru catalysts. The efficiency of the developed method is driven by the addition of compressed CO2 (scCO2), which, in combination with the Ru catalyst, exerts a synergistic effect. ScCO2 plays a pivotal role in removing hydrogen, thereby shifting the equilibrium toward ester formation. The turnover frequency (TOF) of 327.6 h–1 was calculated at a conversion level of ∼10% for this process. This method was also successfully extended to the formation of various esters from their corresponding alcohols, with high selectivity. Spectroscopic analysis revealed significant interaction between the substrate and the catalyst, providing insights into the possible reaction pathway, which was further validated by density functional theory (DFT) calculations. A notable feature of this method is its reversibility: the hydrogenation of ethyl acetate back to ethanol was achieved at a relatively mild temperature of 150 °C. This highly selective and efficient ethanol–ethyl acetate conversion cycle highlights the great potential of this approach for application in hydrogen storage systems.