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Author: Subject: Difference between reducing aromatic and aliphatic nitro groups
ItsAChitzen
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[*] posted on 9-7-2012 at 11:47
Difference between reducing aromatic and aliphatic nitro groups


I have seen the possible reduction of nitrobenzene using iron in acid. Are there suitable conditions for R-NO2 reduction to R-NH2 using iron? I have seen one with iron and acetic acid reflux, but I was wondering whether there was an appropriate set of conditions with HCl or some such. I would also love to know why this is the case, if anyone is up to it.
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chemrox
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[*] posted on 9-7-2012 at 13:05


nitroparafins like nitromethane are easily reduced too. Fe/HCl is a popular reducing agent for them.



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ItsAChitzen
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[*] posted on 9-7-2012 at 13:23


I am assuming that this is accurate whether or not they are primary, secondary or whatnot. Is a reflux necessary? Also, I am assuming that you are using aqueous HCl. True?
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AndersHoveland
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[*] posted on 9-7-2012 at 18:30


There probably are differences between reducing aromatic and aliphatic nitro groups, but I am just not sure what exactly they are.

Phosphine (PH3) can reduce nitrobenzene. There was no reaction at neutral conditions, but when sodium hydroxide was added then azoxybenzene was produced in high yield. PH3 will also reduce 1-naphthol to naphthalene. "Phosphine as a Reducing Agent", SHELDON A. BUCKLER, LOIS DOLL, FRANK K. LIND, MARTIN EPSTEIN. J. Org. Chem., 1962, 27 (3), pp 794–798

As you no doubt are already aware, in the case of aromatic nitro compounds, the presence of other nitro groups on the molecule makes it more vulnerable to reduction. Picric acid, for instance, is reduced for FeSO4 under alkaline conditions to picramic acid (one of the nitro groups is reduced to an amine).


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ItsAChitzen
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[*] posted on 10-7-2012 at 04:26


Phosphine sounds like something I'm going to have trouble getting in the US, but I will look into it.
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