Breaking the Strongest Organic Bonds by Water: Defluorosubstitutions at the Air–Water Interface of Microdroplets

The C-F bond is recognized as the strongest single bond in organic chemistry. Activating such inert bonds typically demands rigorous reaction conditions, often involving expensive transition metal catalysts or harsh reagents. In stark contrast, this study demonstrates reagent-free defluorosubstitution reactions using only water. We observed the selective cleavage of Csp²-F and Csp³-F bonds, resulting in the formation of highly reactive carbocation species and fluoride anions at the air-water interface when aqueous solutions of organofluorine substrates (ArF and ArCF₃) were sprayed into the air. The carbocations formed at the interface subsequently reacted with various nucleophiles to yield defluorosubstitution products. A mechanistic investigation suggests that a one-electron reduction of the aromatic substrate facilitates rapid heterolytic cleavage of the C-F bond, occurring in less than a millisecond. Thus, fluorine, often described as a "small atom with a big ego", has been effectively knocked out of organofluorine compounds by water.