Aromatic Iodination: Evidence of Reaction Intermediate and of the ?-Complex Character of the Transition State

Article abstract of DOI:10.1021/jo00010a013

The reactivity of the four different procedures of aromatic iodination is compared under the same experimental conditions, and their selectivity toward two substrates in competition, i. e., mesitylene (1,3,5-trimethylbenzene, MES) and durene (1,2,4,5-tetramethylbenzene, DUR), is evaluated.Two of these procedures, namely, S2O8^2-/I2 and Ce(IV)/I2, present strong oxidizing capacity.Since the same MES/DUR relative reactivity is obtained from the four procedures, it becomes possible to state that a common reactive intermediate, most likely the I⁺ ion, is generated.The use of the MES/DUR mechanistic probe allows one to describe the reactivity picture of the iodination reaction as one of electrophilic substitution at the aromatic nucleous, with a transition state properly represented in terms of a ?-complex.The radical cation of durene also forms when the iodination is carried out by means of oxidizing agents, but it is solely responsible for the formation of side-chain substitution products and is not involved in the nuclear substitution process.