Today, my chemistry teacher gave the following organic conversion as homework: benzene to 1-bromo-3-iodobenzene.

I tried something like:


I am not sure about it, can someone review my conversion (as I have got an exam tomorrow)?


It looks pretty good overall. The order of substitution is correct to achieve the required pattern but there are two points I would pick up on.

  1. The final substitution of the diazonium salt is best done with $\ce{CuI}$ rather than $\ce{KI}$ as the copper(I) ions catalyse the reaction. Also heating is not required; the reaction can be run at room temperature (or possible slightly above but not much).
  2. The diazonium salt is drawn incorrectly since it is ionic in nature. There is a triple bond between the nitrogens and a formal positive charge on the middle nitrogen, although in reality the charge is delocalised over both atoms:

    enter image description here

  • 1
    $\begingroup$ Do you have an example using CuI for that reaction? I've actually only ever seen KI for the transformation of diazonium to iodide. $\endgroup$ – jerepierre Aug 6 '15 at 20:07
  • $\begingroup$ Interesting, I assumed that iodide would be similar to chloride and bromide but perhaps I am wrong. No I have never actually seen an example. $\endgroup$ – bon Aug 6 '15 at 20:16

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