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Author: Subject: Troubles with the synthesis of Iodobenzene
Rhodanide
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[*] posted on 29-8-2019 at 08:35
Troubles with the synthesis of Iodobenzene


Hi everyone.
I'm currently trying to make Iodoxybenzene, but I've run into trouble at the step where I make Iodobenzene. I'm using the route where Aniline Hydrochloride is Diazotized using HNO2, and the subsequent Diazonium salt reacted with Potassium Iodide to form Iodobenzene. Simple enough, right? Wrong, I'm an Inorganic chemist and this is uncharted territory for me. I need some help. I have done this reaction 3 times and always encounter the following: An unknown, pale yellow solid formed in the addition of the Iodide, and sub-5% yields of a black oil which quickly solidifies upon standing. I'm not progressing, I'm going backwards! More importantly, I'm running out of my precious Aniline! What am I doing wrong? It may seem quite clear to some of you, and if you've got an answer, then please dumb it down (so to speak) for your your I-chem friend here. In a tough spot here and anything is helpful. Well, most anything. :)




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Rhodanide
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[*] posted on 29-8-2019 at 08:37


Note: I'd rather not have to go with the I2/HNO3/C6H6 route, because Benzene is expensive and money is tight.



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Pumukli
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[*] posted on 29-8-2019 at 10:53


Well, I've done a few diazotization reactions eons ago, with KI, but I don't remember the yellow thing. I remember a dark, bubbling reaction mixture though. :)

First thing first: I hope you are following a well-written, checked synthesis route! (Org. synth., Vogel's, etc.)
Which one are you trying to follow?


[Edited on 29-8-2019 by Pumukli]
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draculic acid69
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[*] posted on 29-8-2019 at 22:00


I would have suggested the benzene/hno3/I2 route as it seems like a cheaper easier method that doesn't cost you your aniline but if you don't want to go that route then aniline it is. A while ago I was looking for a write-up on iodobenzene made by the hno3 method but couldn't find it.i think it was melgar or magpie who did it.
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Boffis
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[*] posted on 30-8-2019 at 04:10


Are you using the Organic Syntheses route (copy attached)? I have not tried this reaction but if it not kept it cool enough the diazonium compound can decompose to yield things like diphenyl which is a solid, or other phenolic derivatives particularly if you don't follow the procedure carefully. My experience of diazonium reactions is that they are very sensitive to conditions/temperature/ time etc and that unless you really know what you are doing it is best to follow an established procedure very carefully.

In your specific case are you sure you didn't have an excess of sodium nitrite? This liberates iodine and make the reaction mixture turn dark. I suggest you filter off the solid and add sodium sulphite to the residue to de-colorise the iodine. Then wait to see if the mixture separates.

It might be worth collecting and recrystallising the solid so that you can check its melting point, this would give us a clue to its identity.

Attachment: CV2P0351.pdf (300kB)
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draculic acid69
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[*] posted on 30-8-2019 at 06:13


These diazonium rxn's are meant to be done at like 2'celsius or there abouts aren't they? It's the same as a deamination using nitrite/HCl right? If it is are you sure you're keeping the rxn cold enough so the nitrite gas bubble out without fully reacting?if the addition of reactants is exothermic keeping a thick glass flask as cold as 5'c can be hard to achieve using an ice bath without adding salt or something to help drop the bath temp.
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