THE REACTION OF IODINE MONOCHLORIDE WITH POLYCYCLIC AROMATIC-COMPOUNDS - POLAR AND ELECTRON-TRANSFER PATHWAYS

Several polycyclic aromatic hydrocarbons were treated with iodine monochloride. Although iodination is the predominant reaction of benzenoid arenes, chlorination is the sole reaction with anthracene, phenanthrene and naphthalene compounds (except for 5), whose oxidation half-wave potentials are less than 1.58 V vs Ag/Ag+ (0.1 M). Arenes with higher potentials are unreactive. Naphthalene (9) and its derivatives with mild electron-withdrawing substituents are chlorinated; the exception (5) yields the 1-iodo product (21). The reaction is first order in substrate and second order in ICl. An electron transfer pathway involving radical cation intermediates is assumed. Ion-pair collapse of the radical cation-ICl intermediates is proposed for the chlorinations and radical-pair collapse for the iodination.