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Author: Subject: Noob question about nitration reactions
wmacturk
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[*] posted on 21-9-2021 at 09:08
Noob question about nitration reactions


**Please note, I have zero interest in producing RDX or any explosive compound. I'm asking purely out of curiosity.**

I was reading up on various nitrations, mainly NC and similar, and they all typically involve using mixed nitric and sulfuric acid in various ratios to produce the nitronium ion in situ, which is the agent responsible for nitrating things like cellulose.

By chance, I came across s method for the synthesis of RDX (the explosive compound making up ~90% of C-4). It seemed to literally involve adding hexamine (Hexamethylenetetramine) to fuming white nitric acid -- no sulfuric involved at all.

I was curious why this is the case. What's so special about hexamine that it only requires the nitric but not sulfuric, like so many other nitration reactions? Lastly, what would happen if you WERE to use mixed acids on hexamine, instead of just WFNA?

Apologies if this is in the wrong forum, I'm new here. And to be clear, I'm asking from pure curiosity -- I have absolutely no intention of making RDX. Ever.
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Fery
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[*] posted on 21-9-2021 at 10:19


Hi wmacturk and welcome to the forum!
The information you are looking for is hidden deep in the forum, more than 10 years ago one member explained it here, why H2SO4 is bad idea in the nitration of hexamine:
http://www.sciencemadness.org/talk/viewthread.php?tid=14760&...
Btw even in the nitration with fuming HNO3 there is best to add acetic anhydride to increase yield, it reacts with water coming from the nitration reaction.




If there is a heaven, it seems not to be materially based. Does chemistry exist there and if yes, how does it look like? Are there good souls well supplied with laboratory equipment, glass, chemicals and information?
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Fulmen
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[*] posted on 21-9-2021 at 11:31


Quote: Originally posted by wmacturk  

Apologies if this is in the wrong forum, I'm new here. And to be clear, I'm asking from pure curiosity -- I have absolutely no intention of making RDX. Ever.


That's OK, we don't mind here. As long as you do it for the right reasons and behave responsible you can talk about it. We actually have a board for energetic materials, so don't worry about it.




We're not banging rocks together here. We know how to put a man back together.
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fredsci93
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[*] posted on 21-9-2021 at 16:26


The no sulphuric acid stipulation is quite interesting, since RDX itself is not majorly decomposed in ice-cold nitration mixture, neither is hexamine decomposed in ice-cold nitration mixture (given urea is present). I find it fascinating too, I recommend giving the other RDX threads a read, they outline every question you might have since RDX has been very extensively recorded on amateur forums.

However, as for why no sulphuric acid is used, it's because sulphuric acid breaks hexamine into formaldehyde resin and ammonium sulphate, so if you were to add the hexamine to mixed acid it would carbonise and potentially runaway especially if the nitric acid was 70% since the presence of water in the nitration mix seems to runaway much easier.

[Edited on 22-9-2021 by fredsci93]
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wmacturk
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[*] posted on 1-11-2021 at 18:31


Sorry for the late response. That's interesting. Do you have an idea of the mechanism by which H2SO4 decomposes the hexamine? And what do you mean by formaldehyde resin? Just formaldehyde of a resinous consistency, or is there some chemical difference between it and plain ol' formaldehyde?

I gave the synths a shot (mixed acids at ~0°C and WFNA at about -20°C, peaking around 8°C), definitely didn't end up with RDX, in fact not quite sure what I've got. Still working on some solubility tests - hopefully that'll shed some light.

I'm quite sure there was negligible H2O in either synth - the WFNA I used was synthesized from bisulfate and sodium nitrate distilled under vacuum at about 60°C and never touched atmosphere (insofar as I could help it), and i used a receiver set up to allow me to bubble O2 through the distillate to clean up the NOx and any water that may have snuck in. Doubt it was 100%, but definitely not below 98. The sulfuric was 'distilled' (really just boiled the water off in a distillation apparatus) and then passed over 3A sieves until no density change was observed -- again not 100%, but pretty high 90s for sure.

Didn't use any urea, acetic anhydride, or anything though. Maybe I'll give that a go...
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Fery
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[*] posted on 1-11-2021 at 21:48


wmacturk
H2O is a product of the nitration.
The nitration should be performed in acetic anhydride which removes the water created in the nitration reaction.




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theAngryLittleBunny
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[*] posted on 6-12-2021 at 14:49


Quote: Originally posted by Fery  
Hi wmacturk and welcome to the forum!
The information you are looking for is hidden deep in the forum, more than 10 years ago one member explained it here, why H2SO4 is bad idea in the nitration of hexamine:
http://www.sciencemadness.org/talk/viewthread.php?tid=14760&...
Btw even in the nitration with fuming HNO3 there is best to add acetic anhydride to increase yield, it reacts with water coming from the nitration reaction.


Is it really such a good idea to mix an organic liquid into fuming nitric acid? Isn't this a bit dangerous, or am I overreacting?
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fredsci93
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[*] posted on 6-12-2021 at 15:20


Quote: Originally posted by wmacturk  
Sorry for the late response. That's interesting. Do you have an idea of the mechanism by which H2SO4 decomposes the hexamine? And what do you mean by formaldehyde resin? Just formaldehyde of a resinous consistency, or is there some chemical difference between it and plain ol' formaldehyde?

I gave the synths a shot (mixed acids at ~0°C and WFNA at about -20°C, peaking around 8°C), definitely didn't end up with RDX, in fact not quite sure what I've got. Still working on some solubility tests - hopefully that'll shed some light.

I'm quite sure there was negligible H2O in either synth - the WFNA I used was synthesized from bisulfate and sodium nitrate distilled under vacuum at about 60°C and never touched atmosphere (insofar as I could help it), and i used a receiver set up to allow me to bubble O2 through the distillate to clean up the NOx and any water that may have snuck in. Doubt it was 100%, but definitely not below 98. The sulfuric was 'distilled' (really just boiled the water off in a distillation apparatus) and then passed over 3A sieves until no density change was observed -- again not 100%, but pretty high 90s for sure.

Didn't use any urea, acetic anhydride, or anything though. Maybe I'll give that a go...


I meant formaldehyde of a resinous consistency, it's also black due to some dehydration by the sulphuric acid. as for the nitric acid from sodium bisulfate + sodium nitrate If the temperature of the mix was only 60C then you most likely have sodium Bisulphate monohydrate since anhydrous sodium Bisulphate melts at 180C, which would mean the nitric you produced was likely azeotropic as the water from the Bisulphate will come over with the nitric acid.

Also you shouldn’t use molecular sieves for drying acids since molecular sieves are decomposed by acid, so you end up contaminating the acid and not taking out much water since the pores get screwed.

I recommend using making RDX using the Keto-RDX method with urea, it's quite difficult but it gives alright yields and works well. (file attached) the mix of Keto-RDX and RDX is slightly more powerful than RDX on it's own which is another bonus

As for what TheAngryLittleBunny said, acetic anhydride is safe to add to nitric acid, there is no hypergolic reaction or decomposition.

Attachment: Synthesis+of+Keto-RDX+and+its+Characterizations+Calculation (3) (6).pdf (1.1MB)
This file has been downloaded 21 times

[Edited on 7-12-2021 by fredsci93]
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