Catalytic Oxidation of Carbon-Halogen Bonds by Water with H₂ Liberation

The unprecedented catalytic oxidation of carbon-halogen bonds to carboxylic acids using water as the oxidant is disclosed. Compared to previous traditional oxidation reactions, this transformation avoids the use of sacrificial oxidants and liberates useful hydrogen gas as byproduct, presenting an efficient method. Catalyzed by an acridine-based PNP-Ru pincer complex, a series of primary aliphatic and benzylic halides were successfully converted into carboxylic acids in high yields. The oxidation of secondary halides, which yields ketones, was also accomplished efficiently. Moreover, the oxidation of challenging C-F bonds, aliphatic chlorides, and bromides has been achieved for the first time. With further improvement, this method could be effectively utilized in the efficient scale-up synthesis of the phenoxybutyric herbicide, MCPB. Furthermore, a formal anti-Markovnikov oxidation of nonactivated olefins to carboxylic acids has also been demonstrated through a two-step sequence involving anti-Markovnikov hydrobromination followed by oxidation of the resulting alkyl halides.