The catalytic effect of iodine and hydrogen bromide on aromatic bromination

Abstract

Although many aspects of aromatic halogenation have bean investigated, little systematic kinetic work has been done with a view to elucidating the mechanism of substitution. In this introduction, which reviews the kinetics and the mechanism of aromatic halogen, discussion is confined to reactions in the dark. A number of theories, with little experimental basis were held by early workers. For example, Williamson (1) considered that dissociation of the aromatic molecule preceded chemical reaction. Kekulé (2) represented halogenation as an addition of the halogen across the double bond, followed by elimination of the halogen acid. Another view was that the substituting group first formed a complex with the directing group and then underwent intra-molecular migration. (30). An ionic mechanism for aromatic substitution was first suggested by Lapworth (31).