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?
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.
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.