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Author: Subject: Why can concentrated sulfuric acid not be used to make RDX ?
AndersHoveland
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[*] posted on 29-4-2012 at 17:29
Why can concentrated sulfuric acid not be used to make RDX ?


It is well known that concentrated sulfuric acid is a useful dehydrating agent for nitrations. But from everything I have read, RDX can not be formed using concentrated sulfuric acid. Either 98-100% HNO3 is required, or acetic anhydride is needed for the synthesis, as some different type of strong dehydrating agent is needed.

The lowest level of HNO3 that has been successful in direct nitration was 91% (Bachmann). Yields get progressively worse the further one moves away from the anhydrous concentration.

Why does sulfuric acid ruin the yields for trying to make RDX ?

Apparently a mixed acid nitration on hexamine can produce DPT, which could then be used as a precursor to HMX.
http://www.sciencemadness.org/talk/viewthread.php?tid=19103
DPT is also a nitramine explosive. Why can DPT be made with sulfuric acid, but not RDX?

First, allow me to make some speculation as to why this might be...

Sulfuric acid behaves as an adduct of SO3 with H2O, in several ways. We commonly think of sulfuric acid as having the structure
HO-SO2-OH
but actually one of the hydroxy groups tends to get protonated.
[+]H2O-SO2-O[-]
When SO3 reacts with water, an the H2O acts as a lewis base towards the SO3, which is a lewis acid. The oxygen atom becomes electron donating toward the other oxygen atoms in the SO3, and a new bond with the sulfur atom is formed. Positively charged oxygen atoms are essentially trivalent (it is actually more complex, but I will not describe it here).

So the SO3 component in concentrated sulfuric acid can break away from the H2O and preferrably form an adduct with amines instead. (more dilute sulfuric acid exists as bisulfate or sulfate anions, not an adduct)

I think perhaps the reason sulfuric acid can be used to make DPT is because the molecule of DPT has free tertiary amines with which charged sulfuric acid adducts can bind. These charges could shield the molecule's nitramine groups from further interaction, at least long enough for the DPT to be isolated.

I do not think sulfuric acid can be used to make RDX. If it was this easy, the industrial process would be using normal mixed acids rather than resorting to expensive highly concentrated (98%+) nitric acid or even more expensive acetic anhydride.

But sulfuric acid apparently can work to form nitramine explosives on amides (such as acetamide, not to be condensed with the amide ion NH2[-]). This is why I suspect "di-keto" HMX might be able to be formed using sulfuric acid.
https://www.sciencemadness.org/whisper/viewthread.php?tid=47...

Do any of the other members know anything about why sulfuric acid fails to make RDX ?
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Hennig Brand
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[*] posted on 30-4-2012 at 16:50


I am not a chemistry whiz, but I was under the impression that RDX, its intermediates or maybe both, was hydrolysed by H2SO4.

HNO3/H2SO4 mixed acids would definitely be used to produce RDX industrially if it was feasible.

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AndersHoveland
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[*] posted on 2-5-2012 at 22:59


Quote: Originally posted by Hennig Brand  
I am not a chemistry whiz, but I was under the impression that RDX, its intermediates or maybe both, was hydrolysed by H2SO4.


But why is it that the sulfuric acid hydroyses RDX, but not the nitric acid? It seems it is not just about the hydrogen ions.
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[*] posted on 3-5-2012 at 06:37


I'm am going to see if I can explain this.
Although both nitric and sulfuric acids may have SOME water, the nitric will always be physically lower in viscosity and the control of the hydrolysis & assorted side reactions can be more efficient. Obviously the best efforts are through DRY HNO3 where 60-70%+ yields might occur. It's also imperative that the nitration must take place immediately and the solution drowned immediately. Amines are not esters and there is a critical time period wherein this takes place. What's more in classic RDX production often the "hexamine" is made in situ from ammonia gas and formaldehyde & once solidified; is immediately exposed to dry or nearly anhydrous HNO3. The reaction and production is relativity fast. What's more it simply doesn't need H2SO4 to dry the nitric acid; all that actually happens is additional side reactions. {This may be why most plant-production of RDX IS the simple nitric acid exposure and not the other lab-level Bachmann complications using solid nitrates, etc.} The actual solidification from precursor introduced into nitric is fairly fast; leave it longer and you get no greater yield, no stronger "nitration", no greater purity - - simply side reactions that can ruin a batch in exposures [that sit in the acid] beyond the ratio of weight of precursor to nitric acid (Bachmann had a simple formula for this on a gram scale, but I don't think it's applicable in plant-level weight) It's simply sampled after 20 minutes (through an hour). and not allowed to rest in the HNO3. Of course there is no need for sulfornation or shielding of the hexamine nor a sulfur atom: it simply would complicate the reaction.
Basically the reasons are logical and straight forward. It's a fast and time critical reaction and the other elements of using a "mixed acid" have no bearing on this material.

[Edited on 3-5-2012 by quicksilver]




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[*] posted on 24-10-2012 at 21:40


Well from what I understand .... RDX and H2SO4 can get along with each other.
http://www.energetic-materials.org.cn/hnclen/ch/reader/creat...
This paper talks about using HNO3/H2SO4 nitrating mix to first make Dinitrourea and then add Hexamine or HDN to the mix..
This affords a mix of RDX and Keto-RDX (K-6).
Can anyone verify this ?




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[*] posted on 8-12-2012 at 22:07


The book is mentioned the chemical properties of RDX.
This is a Chinese book, need to be translated.
It's has pay attention to this problem when I read this book.


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[Edited on 9-12-2012 by detonator]

[Edited on 9-12-2012 by detonator]

[Edited on 9-12-2012 by detonator]
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AndersHoveland
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[*] posted on 9-12-2012 at 03:29


Quote: Originally posted by detonator  

This is a Chinese book, need to be translated.

The equation shown in the book shows RDX reacting with sulfuric acid to form formaldehyde, nitrosylsulfuric acid, elemental nitrogen, and water.

The initial acid-catalysed hydrolysis of RDX into formaldehyde and free nitramine is probably reversible. Presumably it is the nitramine that goes on to be dehydrated by the sulfuric acid.

This could also explain why nitramines of acetamides, R-CO-NH-NO2, seem to be able to be formed in the presence of sulfuric acid.




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