Master Organic Chemistry Reaction Guide

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

  1. Advances in the Synthesis of Iodoaromatic Compounds
    B. Merkushev
    Synthesis 1988; 1988 (12): 923-937
    DOI: 10.1055/s-1988-27758
    A slightly dated (but still relevant) review on various methods for the synthesis of iodoarenes. This includes electrophilic iodination methods.
  2. 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
    DOI: 10.1021/jo00835a055
    A simple and straightforward method for synthesizing monoiodoarenes using CuI2 as the iodinating agent.
  3. 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
    DOI: 10.1021/jo00063a052
    A synthetic method for electrophilic iodination by Nobel Laureate Prof. G. Olah using NIS in a superacid./private_ReactionGuide]


Comment section

5 thoughts on “Iodination of Aromatics with I2

  1. Does reaction of molecular iodine with nitric acid not produce iodobenzene in greater yield? Lesser yield? Just as good?


        1. My text said that HI is a reducing agent.(That’s why direct Iodination fails to give Iodoalkane. Prescence of oxidising ahents like HgO is required to oxidise hydrogen iodide to iodine gas)

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