Regioselective Para Chlorination of Activated Aromatic Compounds

Article abstract of DOI:10.1021/jo00212a029

A series of 2-alkylphenols were chlorinated with chlorine, sulfuryl chloride, and sulfuryl chloride catalyzed with a divalent sulfur compound a metal halide.The latter chlorinating system is the most regioselective for both para chlorination and for the degree of chlorination, i.e.,monochlorination.The selectivity is also demonstrated for 2-halophenols, 3-substituted phenols, and aromatic ethers.The reactive intermediate is proposed to be +>-> which explains the selectivity to the para isomer due to the bulkiness of the chlorinating agent.The observed differences in isomer distribution with the studied phenols are explained by the degree of hydrogen bonding of the phenol as seen in the IR and NMR as well as the differences in reactivity.