Spontaneous α‐C−H Carboxylation of Ketones by Gaseous CO₂ at the Air‐water Interface of Aqueous Microdroplets

We present a catalyst‐free route for the reduction of carbon dioxide integrated with the formation of a carbon‐carbon bond at the air/water interface of negatively charged aqueous microdroplets, at ambient temperature. The reactions proceed through carbanion generation at the α‐carbon of a ketone followed by nucleophilic addition to CO 2 . Online mass spectrometry reveals that the product is an β‐ketoacid. Several factors, such as the concentration of the reagents, pressure of CO 2 gas, and distance traveled by the droplets, control the kinetics of the reaction. Theoretical calculations suggest that water in the microdroplets facilitates this unusual chemistry. Furthermore, such a microdroplet strategy has been extended to seven different ketones. This work demonstrates a green pathway for the reduction of CO 2 to useful carboxylated organic products.