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I'm working in the lab with a very old (like 30 years old) sample of 4-nitrophenol, wich of course has been reduced with the time to 4-aminophenol. I need to isolate both reagents and work only with the nitrophenol, is there any quick way to do that?

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    $\begingroup$ There are various products of reduction of nitrophenol. Best way would be to cast it aside and buy fresh one. $\endgroup$ – Mithoron May 11 '18 at 17:30
  • $\begingroup$ @Mithoron, I'm screwed, I'm in Cuba, there are no such things in here. I'm trying to get a fresh one, but that's really difficult here :) $\endgroup$ – Marange May 11 '18 at 17:39
  • $\begingroup$ One has to ask if the container of 4-nitrophenol was left open during the 30 year period and was it stored in plastic or glassy bottle? Another thinking is that, what was the expiring date for 4-nitrophenol? Like drugs which are also chemicals have expiring date labelled on the container before it goes into the market. Then what taught brought the question raised, however, if you are just assuming, the answers given by Mathew Mahindaratne may be useful. Omar A.Wafudu $\endgroup$ – Omar abdullahi wafudu Aug 6 at 4:39
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I would use solvent extraction. Dissolve the mixture of phenols in an organic solvent. Next shake the organic solution with dilute hydrochloric acid in a separation funnel. Do this several times to wash all of the 4-hydroxyaniline out of the organic phase.

Next shake the organic phase with concentrated sodium chloride solution (brine) and then add anhydrous sodium sulfate. Shake the mixture up in a sealed conical flask. Now decant or filter it to give you a solution of 4-nitrophenol which you can now evapourate down to give you the phenol.

I would like to know how the nitrophenol was reduced into the amine over the years it was in storage. This is a more interesting question to my mind is how did the nitro compound get converted on storage into the amine.

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    $\begingroup$ It is a very good question you brought up here. It's usually other way around. Aryl amines air-oxidize. I never heard of nitro to amine reduction by air. $\endgroup$ – Mathew Mahindaratne May 11 '18 at 17:09
  • $\begingroup$ @MathewMahindaratne, thats a good point, I checked the compound by UV-vis, and there is a strong band from 250 nm - 400 nm. I expected only to see the signal around 400 nm. The p-amminophenol absorbs around 250 nm, that's why I conclude that it's the impurity. Of course further analysis is needed, but that's all I can say by now. Again, is a 30 years old reagent stored in very, very bad conditions, anything could have happened to it. Air is the just the tip of the iceberg $\endgroup$ – Marange May 11 '18 at 17:35
  • $\begingroup$ @Marange Like everything absorbs around 250. I'm afraid wild guessing isn't good idea. $\endgroup$ – Mithoron May 11 '18 at 20:33
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I would expect 4-nitrophenol to be relatively stable, even when stored for a long time under air, and as Nuclear Chemist says I would certainly not expect any reduction of the nitro group over time.

Have you tried simply recrystallizing the material you have. In Armarego and Chai it has been purified by recrystallization from aq. HCl (0.5N), aq. H2SO4 (1N), EtOH, aqueous MeOH, CHCl3, benzene and Pet Ether. Give any (or all) of the above a go. The expected melting point is 113-114 C so you can check your material for purity without access to any expensive analytical equipment.

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