Iodination of Aromatics with I2
Description: Treatment of an aromatic such as benzene with iodine (I2) and copper (II) chloride leads to formation of the iodinated benzene.
Notes: CuCl2 is a catalyst for this reaction. The byproduct is hydroiodic acid (HI)
Notes: The byproduct of each of these reactions is HI
Mechanism: This is an electrophilic aromatic substitution reaction. The reaction begins with iodine attacking Cu (Step 1, arrow A). This takes electron density away from I2, making it a better electrophile. Attack of the aromatic π bond on iodide (Step 2, arrows B and C) then breaks aromaticity and leads to the carbocation. Removal of a proton from the carbocation (Step 3, arrows D and E) reforms the π bond, leading to the formation of the iodobenzene product.
Notes: Note how CuCl2 is regenerated at the end of the reaction.
It’s also reasonable to show breakage of the I–I bond before the aromatic attacks, such that the aromatic is attacking I(+).
(Advanced) References and Further Reading
- Advances in the Synthesis of Iodoaromatic Compounds
Synthesis 1988; 1988 (12): 923-937
A slightly dated (but still relevant) review on various methods for the synthesis of iodoarenes. This includes electrophilic iodination methods.
- Halogenation with copper(II) halides. Synthesis of aryl iodides
William C. Baird and John H. Surridge
The Journal of Organic Chemistry 1970, 35 (10), 3436-3442
A simple and straightforward method for synthesizing monoiodoarenes using CuI2 as the iodinating agent.
- Synthetic methods and reactions. 181. Iodination of deactivated aromatics with N-iodosuccinimide in trifluoromethanesulfonic acid (NIS-CF3SO3H) via in situ generated superelectrophilic iodine(I) trifluoromethanesulfonate
George A. Olah, Qi Wang, Graham Sandford, and G. K. Surya Prakash
The Journal of Organic Chemistry 1993, 58 (11), 3194-3195
A synthetic method for electrophilic iodination by Nobel Laureate Prof. G. Olah using NIS in a superacid./private_ReactionGuide]