I am working with aromatic nitro compound and reduce the nitro to amine by using hydrazin with Pd/C at 70°C. in ethanol. after refluxing for 8h , i filtered the precipitate and washed with ethanol. the solution was cooled to room temperature and poored into water. i filtered the white precipitate. but a little later my white monomer turned into pink monomer. i would like to ask why? this is unexpected.
After reduction, You obtained compound which have aniline core. It is well-known that aniline easily oxidized by oxygen of air to give colored mixture of compound. The color depends on structure but rose and red color are included.
Moreover, the oxidation is possible even at presence of traces of oxygen, for example if you do all procedures in argon atmosphere, but forgot to degasing of water or ethanol.
In basic media, nitro compounds turned into pink. you should wash thoroughly solid with water after filtration.
thank you for quick reply. i washed with water but again it was pink. should i continue refluxing a few more hours?
in basic condition, reduction of nitro compounds yield the corresponding
azoxy, azo and hydrazo compounds in varying amounts. you can choose, another reducing agent: Fe/HCl, SnCl2/ HCl,...
hmmm i see. then the best solution is that trying to another reducing agent.
After reduction, You obtained compound which have aniline core. It is well-known that aniline easily oxidized by oxygen of air to give colored mixture of compound. The color depends on structure but rose and red color are included.
Moreover, the oxidation is possible even at presence of traces of oxygen, for example if you do all procedures in argon atmosphere, but forgot to degasing of water or ethanol.
Reduction using a different reducing agent like H2/Pd or Fe/HCl may be the answer to produce a white product.
Another possibility is to treat the product you have with activated carbon to see if you can remove the colored impurity in your product.
The pink color is almost certainly due to air oxidation of what is probably a minor by-product.
I would try formic acid, or ammonium formate, instead of hydrazine. Recrystallizing the nitro compound, so as to have a more pure starting material, might also be helpful.
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