Keras
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One pot reduction of dinitro compounds to diamines
Folks,
does anyone have experience with one-step reduction of dinitro- compounds? I’m planning to reduce my recently made dinitrobenzene into
m-phenylenediamine. Apparently I cannot use my favourite reductant, sodium hydrosulphite, because the reaction would stop halfway there (at
m-nitroaniline).
Vogel describes a process that uses zinc and sodium hydroxide to make o-phenylenediamine, but starting from o-nitroaniline. So I probably could use
hydrosulfite then zinc, but I'd rather use a single-step process.
I also considered the use of tin (II) chloride, but I can’t find much info on it. I have a paper stating that it works well in ethyl acetate or
ethanol, but the examples of reduction given are always mono-nitrated.
Anyone with experience in this?
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bnull
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What about electrochemical reduction: R. Chandra, P. N. Anantharaman, H. V. K. Udupa, Electrolytic Reduction of m-Dinitrobenzene to m-Phenylene
Diamine. Journal of Indian Chemical Society, Vol. 53 (Jun 1976), 627–629. https://doi.org/10.5281/zenodo.6395640
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Keras
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Well thanks!  But I can’t locate that paper, and I have zero equipment for
electrolysis, really. No electrodes. Just a power supply, but I doubt that suffices, unless you can use stainless steel flatware as electrodes
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kmno4
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Fe + HCl(aq) ... and this is all.
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Keras
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Lol, yeeees I mean, solvent, temperature, time?
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Texium
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Ethanol, reflux, as long as it takes
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Keras
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Thanks Tex!
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kmno4
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| Quote: | | Lol, yeeees I mean, solvent, temperature, time? |
Yeeeeeeeeeeeeeeeeeeeeeeeeeeeees, it is 100 years old procedure.
Read some literature or this one : West R. W., J. Chem. Soc., 1925 (127) 494.
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Keras
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Béchamp was not born yesterday, lol.
But it is remarkable how little information is available on this reaction nowadays.
Thanks!
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Keras
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OK, I somehow botched it. Did what was described in West (1925) anddddd… I figured out it would be clever to use magnetic stirring during the
reduction, but it turned out that most the iron was attracted to the bottom of the flask (and the stir bar) and it resulted in ‘iron caking’, a
big solid crust of mixed unreacted iron filings and iron oxides. Broke up the cake (with difficulty), filtered → some iron oxides passed through.
The resulting mixture is so dark brown that it is impossible to know if the reaction succeeded or not. Distilled almost all the methanol which seems
to co-distill with a yellow compound that I assume is 3-nitroaniline, given that the reduction was probably incomplete. I was left with a dense dark
brown mixture that I treated with 36% HCl just in case some amine hydrochloride would precipitate out. Didn't really have time to carry on, so I’ll
pick up on that later. I’ll probably filter out what's in that flask, join with the yellow methanolic solution and restart the reduction this time
using a vanilla heating mantle.
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kmno4
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Yes, it happens especially if someone does this for the first time.
Another bad thing is using iron powder.
The best are iron ~cm x cm strips, or just steel nails, whatever similar, even rusty scrap.
Amount of HCl should be proportional to amount of nitrocompound used : 1 mol of HCl per 1 mole of NO2 + 5% excess. Solvent : water/methanol(ethanol,
IPA...) 90-80/10-20 w/w.
The best reaction vessel is glass or PP botle, with very often shaking (manual). Under these conditions, amine hydrochloride remains in solution, iron
and its oxides remain as sediment. If everything is OK, no hydrogen is produced. HCl(aq) may adding in portions. At larger scale, the mixture becomes
warm, but there is no need to cool it down.
Iron (hydr)oxides stains are best removed by citric acid solutions.
PS. I have strong impression that I wrote something very similar years ago at SM ....
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Keras
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I used iron fillings which was a sort of halfway house. And I didn't use that much of HCl, probably less than 20 mL, since the paper you gave me told
that FeCl₂ was regenerated in the course of the reaction by reaction of FeCl₃ with Fe. I don’t think hydrogen was given off, though of course
it’s difficult to say.
I used pure methanol though, with water coming from 23% HCl.
I usually remove iron stains using oxalic acid, but citric acid is probably a cheaper alternative.
Thanks for the additional info!
[EDIT]: I suppose most of the product is not lost, so I’ll restart the reaction using a new batch more in line with what you advise.
[Edited on 11-2-2025 by Keras]
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kmno4
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Finally I have found my lost jar with ~10 g of 1,3 dinitrobenzene.
It is by-product from nitrobenzene preparation.
Having nothing to do with this, I am going to "convert" it into diamine derivative with Fe/HCl method, just for fun.
I will report the results.
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Keras
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Quote: Originally posted by kmno4  |
Finally I have found my lost jar with ~10 g of 1,3 dinitrobenzene.
It is by-product from nitrobenzene preparation.
Having nothing to do with this, I am going to "convert" it into diamine derivative with Fe/HCl method, just for fun.
I will report the results. |
Great! Lemme know about it!
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kmno4
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So, I got nothing but very deeply purple-brown solutions.
It is not desired diamine but - most possibly - some azo dye.
My procedure should be modified or totally changed.
Two things.
1. Procedure by West uses "metylated spirit", some HCl(aq), Fe and nitrocompound. What is disturbing - amount of available hydrogen for reduction of
-NO2 groups is far too small in given proportions 
His "metylated spirit" must then contain some larger amonunst of water, acting as hydrogen source.
2. There is an interesting book, available at SM library, giving more realistic procedures and informations about such reductions. Namely it is
"Fundamental processes of dye chemistry", from 1949 year.
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Keras
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| Quote: Originally posted by kmno4 |
So, I got nothing but very deeply purple-brown solutions.
It is not desired diamine but - most possibly - some azo dye.
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Exactly what I got. Nothing but bluish-brown deposits. Thanks for confirming, I thought I had completely botched it.
IMHO, the best way is to use granulated tin and HCl. This is documented in Vogel, p. 893. Although it uses H₂S to precipitate the tin ions, which is
not very practical.
Second best, maybe, is to first mononitrate only, reduce to aniline using sodium hydrosulphite, then nitrate again to get m-nitroaniline, then reduce
with Zn/OH⁻ as described in Vogel, too. More steps, but less harsh conditions and maybe better yield at the end????
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Dr.Bob
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I have made diaminobenzenes before. The best route is H2, Pd/C, ethanol, but I have also used Raney Ni and hydrazine in Ethanol, which is also nice
and easy to work up. Other methods were tin or iron and HCl, which work, but can be a mess to work up. I have used sodium dithionate for a few
reactions, it works OK, but is not always fast or complete. There are others, but I haven't used too many others.
The big challenge for diamines is that most will quickly oxidize to the amino version of quinones, as diamines are electronically similar to
hydroquinones. These are strongly colored and prone to other reactions. Most dimaines need to be acylated or cyclized further to prevent their
oxidation, which can even occur from just air.
If you make monoacylhydroquinone (or the amino varient), it will react with itself (disproportionate) to form diacylhydroquinone and quinone. I
tried once to make a compound that had 2 para nitrogens on a ring, and it only acylated at one of them, and it just would not stay intact for long.
Good luck.
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Keras
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Next time I’ll probably try and run the reduction under inert atmosphere. Thanks for all the advice!
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