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ManyInterests
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OK, so I need to post my latest result that I find very frustrating with RDX synth, especially since what I am supposed to get (or I think I'm
supposed to get).
So I started with 250g or 263g of nitric acid (not entirely sure) the total amount was around 95% nitric acid that has been 100% purged of all NO2 (it
was fully clear, no yellowness or red). I added to this 34.9g of anhydrous ammonium nitrate that I dried for over 24 hours at 90C in the oven, and I
cooled it down to -5C and I added 30.5g of hexamine over the course of 4 hours and never allowed the temperature to rise over 5 or 6C. I then allowed
it to reach room temperature (around 19C) slowly, I then started to heat it slowly with strong stirring throughout. I did hear fizzing coming from the
solution, and fuming started around 50-60C, I continued to heat it until 80C, but I decided not to hold it for 30 minutes as it took me a very long to
get it to that temperature, it emmitted a lot of fumes but I was able to handle it and there was a LOT of fizzing. I let it cool down slowly before
putting it on a salt-water ice bath to let it get down to 0C before I dumped it.
My weird from 30.5g of hexamine was... 13.5g of RDX. It is the lowest yield I got. The last time I did RDX I used the same method (Knoffler if I am
not mistaken) and I got almost the same amount of RDX as I put in in hexamine, but I did have a runaway at the 60C mark and saw red fumes, but I
quickly dumped my beaker in the bucket and stopped the reaction. I wondered if the heating step is needed to go up to 80C or is something like 50C
sufficient? Did I vaporize or destroy my RDX in addition to the other impurities?
I am confused here. RDX is by far the most difficult challenge of any energetic. Much more so than any other. So much time to get the nitric acid
ready and it is all just... bleh.
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greenlight
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In literature, that manufacturing process is held at 55°C. Your lucky you didnt have a runaway reaction. That temperature seems outright dangerous
to heat a nitrolysis reaction (or any nitration other than a C-nitration to). You are providing high kinetic energy to molecules within a "soup" of
an acidified already sensitive compound. I would recommend never going that high again.
The fizzing to me definitely indicates possible side reactions or decomposition of your desired compound. You used colourless fuming nitric acid with
minimal dissolved nitrogen dioxide so something is being decomposed into gas rapidly at that temperature.
It would have been more effective and safer heating at 50 for an extended period.
I recommend the Bachmann process where you first use azeotropic nitric acid to synthesise hexamine dinitrate and then performing a nitrolysis on that
with the same reagents you used for this and a lower temperature. You already have half the nitro groups attached in the case of HDN, with less work
to do in the final nitrolysis resulting in better yields and a smoother reaction at only moderate temperature.
The HDN is an extremely easy nitration and high yielding too.
If you try this method you will be amazed at the difference.
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Alkoholvergiftung
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Dug sayed in his video for the koffler reaction you need 80C. With lower temperatures the reaction with the NH4NO3 doesnt take place. Dont know if
this is true but he looks like an serios source.
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greenlight
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My mistake, you are correct, sorry guys.
I was looking at the reaction scheme for synthesis from only hexamine and excess concentrated nitric acid.
The Koffler process does use temperature of 80°C. It seems it does not follow the traditional nitrolysis pathway where a heat value like that would
result in a runaway.
[Edited on 15-1-2026 by greenlight]
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greenlight
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Found this thread discussing the temperature control and duration for the K process:
http://www.sciencemadness.org/talk/viewthread.php?tid=159924
The fuming can be expected from high purity nitric acid but I still believe the fizzing indicates decomposition occurring.
Maybe an attempt at a slightly lower temperature for a longer duration before the onset of the fizzing would run better?
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ManyInterests
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I am glad to learn that the fizzing was not unique to my experience, and I think what happened is that a lot of my RDX decomposed by the heat. When I
did this the first time (with clean nitric acid and no runaway during addition... a first) I did have a runaway at the 65C mark, but that is probably
because I heated it too fast. However when I recovered the RDX it was around 30.5g from 29.5g starting hexamine. While there might be some mild
impurities I don't think there is enough to impact performance and long-term storage that much, and also it was heated somewhat.
I did read in other literature and videos that heating to 50C is acceptable and sufficient. This is what I will do next time.
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BoroNar
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I've been scrubbing my RFNA for 2.5 days! Yes, about 36hours. Result is same as with dist over sulfuric acid. Slight yellow color is still present.
Seems other approach is needed, fish bubbler route is not effective, thus have lost 20ml (about 10%) to Bicarb scrubber.
It seems more effort is needed to become member of WFNA makers club.
As far as I understand, one must work in a way not to have NO2 released first place, if once introduced in solution, becomes hard to evict.
What are options? What is the sure way to have clear nitric acid instead of red-green-yellow thing?
Always have Sulfuric Acid pre-cooled in freezer
Add KNO3 (dried to death, in hot oven @150deg for many hours) while stirring so no hotspot ever forms, no chance of premature release for NO2
use aspirator vacuum
and above all, use minimal temperature like 40deg or so and wait forever to distill tiny 200ml. Low dist temp also implies incomplete extraction of
acid.
Will try described procedure, does anybody have practical hands on experience to give further advice and recommendation?
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BoroNar
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It seems clearing up RFNA is best done with ozone generator. Even some cheap unit I had access to worked, bubbling for just 1.5 hour was enough to
clean 200ml RFNA.
But stuck to next problem with RDX, same thing as you guys here, K-method produces NO2 at 65c.
Process I am following is from Dug's video, exactly step-by-step, no even miniscule changes.
Tried two times and yes, temperature increase was slow and gradual.
May be impurities come from hexamine? it is from fuel tablets, recrystalized from water, filtered few times with different mesh filters (0.1um PTFE
was the last) dried at low temp under vacuum.
Result was bit more than input hexamine, maybe it is good for first time but how to get that 2 mole result?
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Microtek
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In Urbanski's desription of the K-method, 1000 kg cyclonite requires 480-500 kg hexamine. Calculating on the basis of two moles of RDX from one mole
of hexamine, that is about 65 % yield, ie. 1.65 moles of RDX from one mole of hexamine. I don't think you will get better than that.
There is obviously still a ways to go, so how about your AN? How have you dried it? Ammonium nitrate is notoriously difficult to dry since it tends to
dissolve in its own moisture content when heated. One method is to heat it at ca. 70 C for 18-24 hours, then gradually increasing temp. Other
protocols can also be used, the trend being low heat for a long time. If the AN seems to melt below about 165 C, it still contains water, and that
will impact your yield of RDX.
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BoroNar
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Microtek
Thanks for replying, these times it is very hard to get into forum. I think this is the way "they" are trying to kill last place on internet where one
can to study this matters, help others and share information...
I have dried AN but not at such extreme, used few times in ETN synth with perfect results. Will do that kind of drying process. Also, can vacuum
chamber and silica gel dehydrate AN?
Here are my calculations for 1.65 molar ratio, still very bad result.
Hexamine input Grams 5
Hexamine input moles 0.0356668996904113 (5/140.186)
expected molar ratio X 1.65
RDX Expected moles 0.0588503844891787 (0.0356668996904113*1.65)
RDX Expected Grams 13.07 (0.0588503844891787*222.12)
RDX Received Grams 6.2
RDX Received moles 0.0279128399063569 (6.2/222.12)
RDX Mol. vs Hex Mol. 0.47
Still, I can’t find out what causes red fumes @65c. Will try very low speed temp increases, with 20-25min plateaus at every 10deg.
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Microtek
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I made a typo in my last post; 65 % yield is of course not 1.65 moles of RDX pr. mole of hexamine, but rather only 1.3 (since the expected molar ratio
is 2:1). Your yield is 39 % which is a little low but not uncommon in an amateur setting.
Red fumes of NOx indicates either thermal decomposition of HNO3 (not likely at 65 C), reduction of HNO3 by compounds in the mix (likely) or
decomposition of unstable nitration products (also likely).
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