Aromatic Halogenation with Titanium (IV) Chloride in Presence of Peroxytrifluoroacetic Acid

Abstract

Titanium(IV) chloride in the presence of an oxidizing reagent such as peroxytrifluoroacetic acid is shown to chlorinate a variety of aromatic substrates. The substitution orientation patterns suggest that the reaction is an electrophilic substitution process, which possibly involves the intermediacy of hypochlorous acid. Chlorination fails to occur with ring systems bearing strongly deactivating substituents, but it proceeds very cleanly and in high yield with activated rings, e.g. phenol. The reaction conditions are mild and are adaptable for bromination or iodination as well as chlorination.