For the production of iodobenzene one needs a metal chloride salt for the catalyst a iodine metal salt will not work for iodination. Don't make me whip out my org chem book Yes, you should whip it out. And read it. As Osmium has said, nitric acid is used. You should have known this, being a second year chem major. Do you know why iodine is not added to the benzene ring the way chlorine and bromine are? After the posts I read in the novel forum, well... IMHO, nobody is really a chem major until after p-chem, and a little humility goes a long way, as I have learned ..Sorry, I'll go back to minding my own business now....
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