Nitrosonium Ion-Catalyzed Oxidative Chlorination of Arenes

A nitrosonium-catalyzed chlorination of electron-rich arenes has been developed, employing sodium chloride as the chlorine source, molecular oxygen as the terminal oxidant, and either nitric acid or sulfuric acid as the acid promoter. This transition-metal-free protocol proceeds in acetic acid under mild conditions (25-80 °C), affording chlorinated arenes in good to excellent yields. Substrate scope studies highlighted the roles of hydrogen bonding for methoxy-substituted benzoic acids, and the experimental results indicated the formation of H₂O₂ as the byproduct and supported a nitrosonium ion (NO⁺)-catalyzed mechanism. A kinetic isotope effect (KIE) of 1.1 was observed using pentadeuteriophenyl phenyl ether, consistent with the pathway involving a Wheland intermediate.