winnerwalzer
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ETN doesn't want to work... why?
Hello all! I am kind of new here, at least as a commenter. I am trying to make Erythritol Tetranitrate, but for some reason it does not work.
I am not at all new to this thing. I've made ETN several times before, with exactly the same method, and with good results. But now it just refuses to
work. I wonder why? Did some of my chemicals expire or am I doing something wrong? Here is what I am doing:
I use concentrated sulfuric acid which I made from 37% battery acid. I simply boiled 1 liter of it, and it became around 3,5 dl of thick, oily liquid
which looks and works like it was sulfuric acid - there's a good reason to think it is actually sulfuric acid, don't you think?
To 100 ml of sulfuric acid I added 60 grams of potassium nitrate. I acquired it from a fertilizer store in 2006, so it's 5 years old, but AFAIK it
never expires. It dissolves fairly well, creating a somewhat thick slurry.
Now I cool this slurry in an ice bath to around 8-9 Celsius degrees (~46 F) and start adding 15-20 grams of Erythritol.
Now the problem is that it doesn't look like nitrating at all. Temperature does not rise, even if I start shoveling it by the spoonful. When I last
made it I had to be careful with this because if I added too much it started fuming. Now it does not. I remember when I last did it I got a white
slurry at the end, but now it stays yellowish.
Regardless of this, if I dump the slurry into cold water, something that really looks like ETN does preciptate. I filtered it, dumped into water again
(5 liters of it), added sodium bicarbonate to get rid of acids (it did not fizzle, so I take it there wasn't any at the second washing), then filter
it through a normal coffee filter paper and let it dry.
What I get is a white powder that exactly looks like ETN and behaves like ETN, but with one exception: it does not work. It withstands the hammer
test, and it doesn't go off when mixed with aluminium powder, however it always did. Instead it deflagrates in the presence of aluminium.
Even funnier that I was able to purify it using methylene. It readily dissolves, re-preciptates when the hot alcohol solution is dumped in cold water,
and the result is exactly the sugar-like crystals, just a bit more shiny, as purified ETN supposed to look.
Gentlemen, please try solving this mystery. The only difference of what I did last time is the sulfuric acid. When I last made ETN I used sulfuric
acid that was stolen from a chem lab, but now I was forced to make my own. So what is wrong?
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winnerwalzer
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Oh, another discovery I just made... If I let it stay in the water, it dissolves. So it's surely not ETN. Why?
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bbartlog
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Is the KNO3 the same batch you used for previous attempts?
Anyway, first suspicion is that your sulfuric acid simply isn't concentrated enough. You don't indicate what precision we should attach to your
measurements, but in any case if you take 1.00 liters of 37% H2SO4 and boil that down to 0.35 liters, then you start with 1280g of liquid of which
474g is actual H2SO4 (density at 37% is 1.28), and end with roughly 80% sulfuric acid by weight at a density of 1.75 (so still 474g of H2SO4, now with
118g of water makes 592g, divided by 1.75g/cc gives you 340ml). I am not an expert on nitrations but I would assume that this concentration of acid is
insufficient for complete nitration.
Boiling down to a volume of 270ml would get you to around 95% acid, but I doubt that volume measurements are really a good way to confirm that your
acid is sufficiently concentrated.
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winnerwalzer
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Yes, KNO3 is the same batch. I got a big pack of it, some 20 kilos so it lasts a while.
I did not measure the sulfuric acid, but now I did. 100 ml weighs around 185 grams. This seems like almost pure, as it supposed to be 1,83 g/cm3. So
it's probably not the acid.
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hissingnoise
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You may be getting incompletely nitrated erythritol; the presence of just one hydroxyl group will render your product soluble.
Try it again using say, 10gm of erythritol!
And it's worth remembering that stored KNO<sub>3</sub> will, despite its appearance, absorb water from moist air . . .
Freshly dried nitrate salt with dry erythritol and 98% sulphuric acid will work every time!
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winnerwalzer
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I see. So I should either dry my KNO3 in the oven or get some fresh, and also use less ETN. Thanks.
This is probably right, because nitration yield from the previous batches was actually less than the Erythritol I added. 15-20 grams resulted in only
half of it. So basically it's still ETN what I got, but has an extra hydroxil group attached?
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hissingnoise
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Most likely you got erythritol tri or di-nitrate, both of which which dissolve slowly in water.
Mixed acid, being the most efficient use of reactants will give the best yields and precipitation of the product will allow you to reuse your
H<sub>2</sub>SO<sub>4</sub>.
A distillation apparatus and fritted filter will set you back a few bob, but you'll not regret the little expense . . .
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winnerwalzer
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Unfortunately I don't have access to nitric acid, that's why I use this method.
I just tried drying some KNO3 in the oven but even after an hour it did not lose any weight. Probably it's not wet then. However I'll go and get some
fresh tomorrow and we'll see. I also melted some Erythritol now and poured into a dry glass vessel to let it cool. That's probably dry enough - it
melts at over 200 Celsius.
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quicksilver
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winnerwalzer :
I would have preferred you continue on w/ an existing thread rather than start a new one. Two members have given you all you could possibly need to
understand the idiosyncrasies of the issue. I would prefer this thread not continue as it repeats well-trodden ground.
If you carefully read the responses, your query was answered to it's maximum: frankly you have answered some of them yourself. It is vitally important
that those basic issues be observed. We have a great deal of information on nitration. Your query is not an uncommon one. The higher you "raise the
bar" in regard to laboratory technique (and even equipment & supplies) the more the issues with a dysfunctional synthesis will become apparent to
you. However as safety & learning being the thrust of this Forum section I can only underline that since we are dealing w/ an extremely serious
subject our level of discourse reflect that. We must avoid "recipes" or "spoonfeedling" in all vital aspects of Organic Chemistry related to this
subject so that our agenda leads us to a greater level of learning first rather than simply a material outcome.
Without unfriendly comments about "using the Search Engine", etc I would point to the rapidity to which you received responses. Many members - even
those with less interest in Energetic Materials - can understand some of the pit-falls herein. Nitration & this particular synthesis itself has a
substantial background experimentation notes available to you.
Thank you for your understanding in this regard.
[Edited on 10-8-2011 by quicksilver]
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winnerwalzer
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Read and understood, thank you & sorry.
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nitro-genes
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KNO3 starts to absorb moisture from the air from 90% humidity onward IIRC, it is unlikely to be your problem, unless it is very impure and mixed with
NaNO3 or you live somewhere in the jungle. I would make sure to check the acid strength again, do it a couple of times to make a better estimate, and
don't cheat while measuring the volume, like I tended to do for my homebrew nitric. 
KNO3 + Sulfuric behaves quite different from HNO3+ Sulfuric during nitrations. KNO3 nitrations are usually slower, especially with crystalline
poly-ols, like mannitol, cellulose or erythritol. Part of it is probably because of the HNO3 needed to be generated in situ, while the solubility and
particle size of the polyol will probably also affect reaction time needed. Nitration of cellulose for example is completed in less than 5 minutes,
for 97% HNO3+H2SO4, though I tended to leave it at room temperature for up to a day for KNO3+H2SO4 to obtain similar quality NC.  Nitration of Mannitol and sorbitol are also much slower, I cant really say for ETN
since I never made it from KNO3+H2SO4, but I think it should behave similarly.
- Both the erythritol and KNO3 should be as finely powdered as possible
- Reaction time should be increased
- Good mixing during nitration itself
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winnerwalzer
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Yeah, thanks. Will try these. However as I wrote my method worked when I tried last time. Will see soon.
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Intergalactic_Captain
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I've never made ETN (though it's been on deck for too many years), but I do have a bit of expxerience with the nitrate-salt methods as applied to EGDN
and nitrocellulose - Nitro-Genes said a bit of what I was going to already, so I'll add what's left...
1 - May be a slip of the tongue, but you say you added the nitrate to the acid, THEN placed it in a cooling bath once dissolved - Bad Idea. Dissolve
the nitrate in a salt/ice bath - It'll take forever, but you'll lose far less HNO3 to evaporation and vastly decrease the possibility (high
probability in my experience) of NOx formation.
2 - By simple math, you have FAR too little available ntric to fully nitrate your erytrhitol - 60g of KNO3 is ~.6 mol, while 15-20g erytrhitol is
1/5-1/6 mol X 3 = ~.5-6mol - I have no literature to back this up ATM, but in a nitration that requires mixed acids you really want around a 50%
excess of available xNO3, if not more, for complete nitation - This is due to many factors, in no particular the equillibrium push, evaporation, NO3+
ion formation, and loss due to NOx formation...Probably more, but my experiments have led to a simple 25-50% excess rule...
3 - Use a bit more H2SO4 - My highest yeilding experiments used a 2:1 rule - For every mol of KNO3 (or NH4NO3) used, 200mL of H2SO4 was used - yours
is closer to 1.5:1, which is more of a slush at proper temperature than a usably liquid mix. Your ratio has worked reasonably well for me with picric
acid, but not for anything else - too much potential for hot-spotting and runaway...
If you see me running, try to keep up.
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