[Twickel]

Hi
I did this reaction in the lab and have a few questions I need to do. Please refer to the image.
Why is temperature control critical during preparation of the diazonium salt, what other nucleophile might react with the diazonium salt at a higher temperature before you add KI?

The sulfuric acid atlow temperatures may react via an electrophillic aromatic substitution reaction. Specifically it is the sulfonic acid which will be added on to the starting material Is that correct? Why does low temperatures stop this from happening though?

Assign the peaks of the mass spectrum of p-iodonitrobenzene please refer to second attached image.
I figured that the heaviest ion is the ion of the entire molecule, the peak at 203 is the molecule minus the NO2 group. I can not figure out the peak of m/z 76. I I tried removing NO2 and the OH group,  What can it be?

Your help is much appreciated.

[discodermolide]

The other nucleophile would be water to give the phenol from the diazonium salt.
I would guess that if your reaction is too slow at lower temperatures the amino group will be substituted by the sulphuric acid to give the sulfonate.
The peak at 76 is the peak at 203 minus iodine, i.e. C₆H₄^2+.

[Twickel]

Thank you for that. Where does the water come from? It can not be sulfonic acid because the question asks for a nucleophile.

Where does the water come from?

[discodermolide]

Presumably you dissolved the sodium nitrite in water added sulphuric acid to form nitrous acid in the presence of the nitroaniline.

[orgopete]

It is difficult to form a phenol, so I doubt that it is water. Nitrite is reported to convert diazonium salts to nitro groups. I presume that is a reason to keep the temps low.

[Twickel]

yes, I diluted sulfuric acid and then added p-nitroaniline to the dilute sulfuric acid

[Twickel]

It is difficult to form a phenol, so I doubt that it is water. Nitrite is reported to convert diazonium salts to nitro groups. I presume that is a reason to keep the temps low.

But in this case, is the only possible nitro source bonded already bonded in p-nitroaniline, so how can it react with the salt which it is bonded to to form a nitro group?

[discodermolide]

You can quite easily get phenols it's a classical Sandmeyer reaction.

[orgopete]

You can quite easily get phenols it's a classical Sandmeyer reaction.

Yes, by heating with sulfuric acid or with a copper catalyst. If it were such a facile reaction, diazotization reactions would be carried out under anhydrous conditions or phenols would be a serious by-product.

[discodermolide]

That's one of the reasons for keeping the temperature down.