Nitrating mixtures - Archive File

[megalomania]

FadeToBlackened
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Posts: 201
From: Hell
Registered: MAR 2001
posted March 18, 2001 09:49 PM
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Forgive me for asking, but why is sulfuric acid used in nitrating things so much? Like T.N.T. nitic And sulfuric acids are used. Why is this?


CragHack
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From:
Registered: DEC 2000
posted March 18, 2001 10:15 PM
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i believe it is used to isolate water molecules so as to get a "dryer" mixture.
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...Æ



c0deblue
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From:
Registered: JAN 2001
posted March 19, 2001 01:04 AM
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CragHack is correct. By binding water molecules H2SO4 effectively "concentrates" the Nitric Acid to a level suitable for nitration purposes. I believe it's accurate to say that in most cases no Sulphuric Acid would be necessary if 99% Nitric Acid could be obtained.


Machiavelli
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Posts: 278
From: Germany
Registered: SEP 2000
posted March 19, 2001 05:10 AM
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When nitrating something you normally have an equilibrium reaction like
Nitric + Shit <=> Nitrated Shit + Water
This reaction has a certain reaction constant depending on concentrations and temperature and pressure etc and it will try to stay in a state of equilibrium.
Let's assume for our example that it's 1:1, the same concentrations of products and educts.
Now when I use concentrated sulfuric acid, it will form a hydrate complex with the water and we'll get a proportion of eg 2:1 because it removes the water from the reaction and we have eg twice as much nitric + shit as we have nitrated shit.
But the reaction wants 1:1 so it'll produce more Nitrated Shit and more water to get 1:1 again. The water gets absorbed again , 2:1, etc, ...


Demolition
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Posts: 159
From: Australia
Registered: FEB 2001
posted March 19, 2001 05:56 AM
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Shit!!!
Sorry but I just couldn't resist.
Demolition



Bitter
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Posts: 293
From: 11 Downing Street, London, England
Registered: SEP 2000
posted March 19, 2001 09:45 AM
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Oh......Shit.
Roughly how much sulphuric acid (99%) would be needed to isolate the water from 70% Nitric acid ? I can't seem to find this information anywhere (I wonder why...).



c0deblue
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From:
Registered: JAN 2001
posted March 19, 2001 12:28 PM
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I'm not a chemist, but Machiavelli's explanation summed things up and certainly increased my own understanding of nitration dynamics. Given the variables in equilibrium reactions it would seem the H2SO4 requirement could be different not only for each substance but for each set of nitration conditions as well. If this is so then perhaps the amount of H2SO4 needed to "concentrate" 70% Nitric Acid to 99% is irrelevant since more or less water would be produced during the reaction itself and thus require more or less H2SO4. Mach, could you elaborate further on this point?


Bitter
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Posts: 293
From: 11 Downing Street, London, England
Registered: SEP 2000
posted March 19, 2001 01:13 PM
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I don't think it's all that important to take the water produced as a reaction by-product into consideration. After all, using 99% nitric acid doesn't need anything extra putting in for it to produce, say RDX or PETN.

[DF90]

From my understanding the sulphuric acid is used with the nitric acid in a nitrating mixture to generate the nitronium ion, which can then electrophilically substitute onto the aromatic ring

HNO3 + H2SO4 -> H2NO3(+) + HSO4(-)
H2NO3(+) -> NO2(+) + H2O

Where a +/- in brackets indicates an ion.

The nitronium ion (NO2+) then substitutes into the aromatic ring producing a H(+) ion that regenerates the sulphuric acid.

H(+) + HSO4(-) -> H2SO4

The sulphuric acid can then react with more nitric acid to produce even more nitronium ions, and is therefore a catalyst to the reaction.

As for the RDX, I am unsure because it is a non-aromatic heterocycle (all the atoms have made all the bonds they can, therefore there are no electrons that can delocalise, and so it is not aromatic?) and so probably doesnt follow the same mechanism, and therefore does not require the sulphuric acid present. Also with RDX it is the N atoms being nitrated, not the C atoms like in the synthesis of TNT.

It might also be possible to substitute other acids in the place of sulphuric for nitration mixtures as the acid is just a source of H+ ions. The general nitration reaction should also require some water present at the start to allow the acids to dissociate into ions, although the reaction does produce its own water. Again the presence of water does not seem to affect the RDX reaction, as Megalomania's synthesis uses 100% nitric acid and methanamine (hexamine).