Sir_Gawain
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First RDX synthesis and questions
Today I attempted an RDX synthesis by the HDN and WFNA method. Firstly, I prepared hexamine dinitrate by dissolving 20g of fuel tablet hexamine in
50 mL of distilled water, filtering out some cloudy impurities, and cooling it to 0*C. 25 mL of cold 70% nitric acid was slowly dripped in with
stirring. After all the nitric was in I let it react for another 15 min and vacuum filtered it. The HDN was washed with about 75 mL of chilled acetone
and carefully dried. I noticed it was not extremely hygroscopic or strong smelling as some reported. Final yield was about 35g. 25g was immediately
used to make RDX.
I cooled 55 mL of slightly yellow nitric acid of about 98% purity to 0*C and added about 1g of ammonium nitrate. The 25g of HDN was slowly added,
keeping the temperature below 10*C. After it was all added, the solution was removed from the ice bath and warmed to room temperature. It was then
carefully warmed to 50*C with a hot water bath and held there for 5 min. During the heating step, some white precipitate formed in the previously
clear solution. After cooling to room temperature it was crashed into 800 mL of cool water. Final yield was a little less than 14g.
Does anyone have any improvements or suggestions? Also, what was that material that precipitated upon heating? The synthesis was mostly taken from
Darian Ballard's videos, although I changed a few things. For example, he used a massive excess of nitric acid: 100 mL for 18g of HDN. Since WFNA is
by far the most expensive and difficult part of the synthesis, it would make sense to optimize yield based on it rather than hexamine.
Also, what solvent is best for recrystallization? Acetone, ethanol, ect.
[Edited on 10-10-2023 by Sir_Gawain]
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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DennyDevHE77
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Hmm, from 30g of urotropine dinitrate, 50 ml of nitric acid (97%), should yield 10g of RDX. So in your case the yield is more than high (although you
took more nitric acid).
In the industry optimize good yield on urotropine, as it is the most expensive, and anhydrous acids in the industry large tonnage and cheap product.
Optimization of nitric acid waste without acetic anhydride is unlikely to be possible.
But you can "neutralize" the spent nitro mixture with sulfamic acid, get DPT, and bring it further to RDX or HMX.
Or you can use sulfamic acid to make the "white salt", potassium perhydrotriazine trisulfonate. And nitrate it with nitrate salt/concentrated sulfuric
acid
[Edited on 11-10-2023 by DennyDevHE77]
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Microtek
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According to Urbanski, 110-119 kg of RDX can be obtained from 100 kg of hexamine by nitration with nitric acid (with no addition of extra ammonium
sources, acetic anhydride or similar things, but with a sufficient amount of nitric acid). I do agree that for the amateur, optimizing the yield based
on nitric acid is more relevant.
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DennyDevHE77
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For some reason I forgot to add yesterday, although the person asked about solvents, the best ones are acetone, DMF, cyclohexanol.
Solubility in acetone (6.81 g /100 g, 12.8 g at 50°C);
Solubility in dimethylformamide (25.5 g /100 g at 20°C);
Solubility in cyclohexanol (12.7 g /100 g at 25°C, 27 g /100 g at 97°C).
As an option there is also fuming nitric acid, but I think it is too expensive, and not necessary.
But think in advance, do you need to recrystallize RDX? The usual treatment of raw-RDX is heating it in 50-60% nitric acid, and then boiling in
distilled water, at that the acidity is reduced to 0.3-0.4%. This acid has no effect on the resistance of the RDX itself. However, over time, as it
releases from the crystals, it may corrode the munition, destroy the binder (in PBX), or interact with components of mixed explosives.
As far as I know, the addition of ammonium nitrate (method K), saves urotropine (which in industry is obviously more expensive than nitric acid), but
still from a liter of WFNA gets 200-250g RDX
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Sir_Gawain
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I ended up recrystallizing it with acetone and it took about 100 mL. I did it mostly because there was a strong smell of NO2 in the bottle it was
stored in. Also, I did heat it in the nitration bath at 50°C for 5 minutes after nitration was complete. The residual nitric acid should destroy most
impurities. I was most concerned with acid trapped in the crystals.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Hey Buddy
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Quote: Originally posted by DennyDevHE77  | Hmm, from 30g of urotropine dinitrate, 50 ml of nitric acid (97%), should yield 10g of RDX. So in your case the yield is more than high (although you
took more nitric acid).
[Edited on 11-10-2023 by DennyDevHE77] |
I havent bothered to check the stoich, but he was adding AN which is like a modified K method. He is using HDN instead of hexamine alone, but no Ac2O
like KA method. The AN addition if done correctly gives two cyclonites per hexamine used if you use 4 eq. HNO3 with 2 NH4NO3 & 1 Hexamine. He is
using HDN which has less than half the heat of reaction compared to hexamine alone. I am not surprised if yields are high from this method. I was
thinking about this but havent tried it, after reading his success, I will work on it a bit. Was going to try this exact approach and if it went well,
transfer it over to the mixed acid K6 procedure as modification in attempt to increase K6 yield... Also planned to test if urea can be replaced by
cyanuric acid to produce the #2 carbonyl on the triazine. There are some patents on carbohydrazide from cyanuric so it seems logical that it could
potentially increase yields on keto RDX versus urea....
[Edited on 16-10-2023 by Hey Buddy]
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Hey Buddy
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| Quote: Originally posted by Sir_Gawain | | I ended up recrystallizing it with acetone and it took about 100 mL. I did it mostly because there was a strong smell of NO2 in the bottle it was
stored in. Also, I did heat it in the nitration bath at 50°C for 5 minutes after nitration was complete. The residual nitric acid should destroy most
impurities. I was most concerned with acid trapped in the crystals. |
I missed your original question on solvents for RDX. Im also working on RDX right now so I have the chart in front of me. RDX is soluble in acetone:
12.8g @ 50 C & 15.27g @58 C (4g @0C). Most common solvents are dismal dissolving RDX.
Also, I have been working on NH4NO3 knoeffler method and its been unsuccessful. I attempted it several times so far but havent been able to maintain
70C long enough. In those cases, my yields have all been in the 70+% range which is also what you are getting, so our experiments line up and I can
tell that my attempts to involve NH4NO3 in reaction are not working because your amount of NH4NO3 is too little to complete K reaction but our yield
percent is the same from appx same concentration of acid. I used 8.6x w:w HNO3 at somewhere between 96-98% based on temp density.
That is what is used in K method. But now I can see that I can pull back the acid qty and expect the same yield. According to Urbanski, The NH4NO3
also has a protective effect on the reaction, and allows safer elevated temperatures even at the range of 30-50 C. Using NH4NO3 is probably helpful as
a margin of safety. Im still working on the K method until I can maintain prescribed temp regiment. If the K method were successful it should yield
high 90% range with the bonus of the protective measure of safety. I found no real benefit of using HDN versus hexamine other than the hdn is mild in
exothermic response and can be added about twice as quickly, saving about 30-45 minutes on small reactions in the ~20g-40g range however, the total
time of preparation and drying of HDN is several magnitudes longer than the time saved over simply using hexamine.
These are my recent observations.
[Edited on 28-10-2023 by Hey Buddy]
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Sir_Gawain
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The reason I added a little NH4NO3 was (as you said) to increase yield. I read somewhere here that even a small amount somehow
helps. The first time I heard of the Knoeffler method was from your other thread.
Ballard used 100 mL of nitric acid for only 19g of HDN, but there was no way I was using that much precious WFNA. I think it would work with even less
than I used. The main reason to use HDN over hexamine is that using azeotropic nitric acid for part of the nitration reduces the amount of WFNA you
need.
Really my main reason to make RDX was to make some oxygen-balanced mixtures with ETN and to explore the process, so I'm not super interested in doing
further experiments in yield optimization due to the large cost in WFNA. But if you can create a high-yielding process suitable for amateurs, many
will thank you.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Hey Buddy
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It does make sense to add NH4NO3, because hexamine forming the triazine could use the NH4 and the Nitrate group could assist in providing additional
concentration. Im unsure if it actually works that way. I do think there is some risk in heating an RDX nitration without the presence of NH4NO3. Ive
never had a detonation though, only run aways. RDX is one of those materials that has had multiple generations of people work on it their whole
career. The furthest they could get in making sense of it was to simply compare yields.
70% yield is really pretty good for RDX prep. Higher concentrations of NA with less concentration of NO2 can squeeze out slightly higher percent, but
with direct nitrolysis of hexamine, about 80% or so is max. You can actually use lower concentrations of NA with loss of yield. Ive read that 80% NA
can yield around 30-40% but the nitration needs to proceed for two hours. Ive done RDX prep with 68% commercial HNO3 and the yield is very low, but it
does provide some yield. Water in reaction of any form is certainly directly correlated with yield loss. The less water present in duration, the
higher the yield.
[Edited on 28-10-2023 by Hey Buddy]
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