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.