# How to convert benzene to 1-bromo-3-iodobenzene?

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:

• Do you have an example using CuI for that reaction? I've actually only ever seen KI for the transformation of diazonium to iodide. – jerepierre Aug 6 '15 at 20:07
• 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. – bon Aug 6 '15 at 20:16