Sciencemadness Discussion Board

HDN Synthesis Problem

Siconic - 14-4-2010 at 21:05

I recently tried to make HDN. This should have been pretty straight forward, and it was.... at first.

I mixed my chemicals, and got a precipitate. Since this was my first batch, it was small. (50ml of hexamine in water)

However, I set it aside, and took a break. When I returned, I swirled the mixture, and all the crystals disappeared!

So what happened? Is this normal? Is there a way to get them back without tossing the mixture? Does this mean that once you get your precipitate you need to filter, or loose your product?

Any help is appreciated. :D

Peroxid - 15-4-2010 at 11:32

You used the hexamin + HNO3 route to synth. HDN?
Anyway you need to filter the precipitated crystals and wash with aceton, and dry it (HDN decomposed to formaldehyde and ammonia when it is wet)

[Edited on 15-4-2010 by Peroxid]

hissingnoise - 15-4-2010 at 11:46

HDN is soluble in water - slow evaporation of the solution will reprecipitate it but it won't be very clean.
If you used the correct amount of acid, fumes shouldn't be a problem.

[Edited on 15-4-2010 by hissingnoise]

greenpick - 10-8-2011 at 11:14

I recently synthesized what I hope is HDN, but I have run into a few problems. My procedure was as follows:
-Mix 28.03 g of hexamine with 100 ml of water. Cooled in ice/salt/water bath to ~5C.
-Slowly added 40 mL of 67% HNO3 cooled in said ice bath, keeping temp of solution in the 9-12C range.
-After approximately half the HNO3 had been added, a precipitate began to form.
-Upon last addition of HNO3, 110 mL of acetone was added to the solution, as I believed this would help precipitate all of the HDN. (probably not necessary, maybe even harmful?)
-Filtered mixture through paper towels, and rinsed with more acetone. (100-200 mL)
-Let paper towel with HDN folded inside sit under a fan until no more acetone could be smelled.
At this point, HDN appeared no different than moist, coarse table salt in all respects (sight, smell, etc)
-The paper towel with the HDN was then placed in a ziplock bag with a shallow bowl of calcium chloride and zipped up. This was left to dry overnight for ~10 hours.

All right, so this is when the problems start. When I opened the bag in the morning, I noticed an extremely pungent, burning odor. I was quite taken aback, and had to step away to take a few deep breaths (more out of surprise than any actual need). There are no visible fumes, but the odor is present even after putting the "HDN" in a plastic bowl and letting it sit in the open air for some time. It doesn't appear to be lessening to a great degree.

Does HDN normally have a pungent odor. The effects remind me of HCl or HNO3 fumes, but the smell is pretty unique. Hard to describe for sure. My only theory is that something in the moist hexamine reacted with the calcium chloride (maybe residual nitric acid, creating HCl?) Any theories as to what this odor is, and how dangerous it may be?

hissingnoise - 10-8-2011 at 12:10

HDN, (C<sub>6</sub>H<sub>12</sub>N<sub>4</sub> • 2HNO<sub>3</sub>;) has as you see, 2HNO<sub>3</sub>, weakly bound.
The small quantity of evolved NOCl in the mix would account for the 'uniqueness' of the smell . . .
'Substantially the same as reacting HNO<sub>3</sub> with NaCl!

greenpick - 10-8-2011 at 13:59 you think it's possible that the HDN and CaCl2 reacted even though they weren't touching? I would think it's more probable that residual HNO3 vapors were the culprit. Oh well, different mechanism, same result.

After looking up NOCl on wiki, I can see how HNO3 would combine with any HCl that may have formed to produce NOCl by this reaction:
HNO3 + 3 HCl → Cl2 + 2 H2O + NOCl
A mixture of chlorine and nitrosyl chloride gasses would certainly explain the pungent, irritating nature of the vapor!

One more thing; how would this contamination affect an RDX synthesis, if at all? Would air drying the HDN be enough, or is HDN appreciably hygroscopic? I plan on reacting 2.5 mL home distilled HNO3 per gram of HDN. (once I get my distillation setup, that is) I will try a small synthesis (~10 g HDN), unless anyone can think of a reason it would be exceedingly dangerous.

quicksilver - 10-8-2011 at 14:07

Did you check pH? Do you have access to melting point equipment? A quick check of some more modern authors doesn't make note of odor, but that doesn't mean it couldn't exist (Cook, Meyer, etc don't note it). However You make mention of continued odor after exposure to atmosphere circulating air, etc. hexamine is basic (ammonia) - to swing it over (your synthesis) would need a great abundance of acid. If nothing else do you observe deliquesce or some physical feature of release?

Subjective interpretations of smells are just too tough to categorize.

[Edited on 10-8-2011 by quicksilver]

greenpick - 10-8-2011 at 14:26

Quote: Originally posted by quicksilver  

Subjective interpretations of smells are just too tough to categorize.
[Edited on 10-8-2011 by quicksilver]

That was my exact thought when I was trying to describe the smell in my first post. There is nothing I can really compare it to, although (I know this sounds crazy) it seems like I've smelled it before, but I just can't put my finger on it. That's probably the chlorine if the above reaction was accurate to any extent.

And no, there doesn't appear to be any visual signs of release. The HDN looks uncannily like table salt: a.k.a. it is a perfect, glittering white substance with large, slightly flattened crystals. Unfornutely I don't have access to melting point equipment, but I will check the pH with some pH paper later today. I will continue to leave the HDN out in open air, as it continues to slowly lose weight. If my calculations are correct, theoretical yield would be around 50.4 grams, and I have about 51 g of material.

I checked the pH by just sticking aquarium pH paper into the crystals, and I got a result of ~7.5! Now there is no doubt that this isn't a 100% accurate result, but you would think the pH paper would stay its normal color, rather than go through the work of showing a basic result. This tells me that it is atleast somewhat basic. Shouldn't it be nuetral, or even slightly acidic though?

I'm thinking of dissolving my HDN in the minimum amount of water, and adding 67% HNO3 until the solution is acidic. (~6 pH) This shouldn't take much. I will then filter and rinse as before, but omit the CaCl2, and see if I get better results.

[Edited on 8/11/2011 by greenpick]

hissingnoise - 11-8-2011 at 01:51


One more thing; how would this contamination affect an RDX synthesis, if at all?

RDX is most conveniently prepared by adding hexamine, in small portions, to strong HNO<sub>3</sub> at <30°C . . .
Forget HDN; it's an unnecessary complication!

quicksilver - 11-8-2011 at 06:48

I will try to find detailed info on HDN characteristics. So far I have only found the most general material. It is a puzzle - I haven't heard of a "strong odor" issue previously.

Microtek - 11-8-2011 at 07:22

HDN often decomposes, producing formaldehyde if the temperature gets too high at some point, or sometimes if impurities are present. Formaldehyde certainly has a pungent smell but of course, so does a number of other compounds.
I suggest recrystallizing the salt from dilute nitric acid and leaving out the acetone. There is no problem with using CaCl2 in the desiccator, but make sure that you don't place it somewhere warm (especially while it is still moist).

Phantom - 14-8-2011 at 01:15

Try to make HDN with 30% HCl instead of HNO3. I made my HDN with HCl. I dissolved some AN in water then I added hexamin and HCl and a little denaturated alcohol.