5-ATZ(5-Aminotetrazole), the nitrotetrazolate ion and friends

Synthesis of 1-Diazidocarbamoyl-5-azidotetrazole (C2N14)

So, for quite a while now I‘ve been wanting to try making some 1-diazidocarbamoyl-5-azidotetrazole, commonly referred to as “azidoazide azide“, as it’s one of the more chemically interesting energetics in my opinion, and it has quite a reputation of being the most sensitive one out there. While the second claim has pretty much been disproven by YouTubers like ReactiveChem and Explosions&Fire [1][2], for being completely heavy-metal free I still consider it to be quite an impressive substance, and kinda wanted to see for myself.


Fig.1: Chemical structure of C2N14

I‘ve started this project around two years ago with the synthesis of disodium azobistetrazolate pentahydrate, but I never really came around to continuing since then, so the salt had been sitting in storage ever since. This finally changed last week, and I managed to successfully make the desired tetrazole, as detailed below.

The 1961 approach by Grundman and Joseph [3]:

This is the approach most generally employed, and the synthetic details are given in Engager’s publication, which was my primary source for the entirety of the preparation [4].
The synthesis starts from 5-aminotetrazol (5-ATZ), which gets oxidatively coupled to the above mentioned azobistetrazolate, which then serves as a precursor to the isocyanogen-system by reaction with elemental bromine. The resulting tetrabromide can then undergo simple substitution with azide, and the resulting “open form“ of C2N14 (isocyanogen tetraazide) quickly cyclizes resulting in the desired end product.


Fig.2: The 1961 synthesis of C2N14

Disodium azobistetrazolate pentahydrate:
As I did this synthesis quite a while back, and my labnotes were rather scattered at the time, I unfortunately don’t have any of my experimental details on hand, though in the end I just followed the procedure given in [4] pretty much exactly, only adding the potassium permanganate as a saturated solution rather than as a solid, so by checking on it you should still be able to follow.
As one may expect from the nitrogen-rich structure this intermediate is already an energetic itself, and while testing some crystals of it on some aluminum foil does cause some rather significant damage (footage of some of its detonations can be found in Extractions&Ire‘s video covering this preparation [5]), as it’s a pentahydrate salt it’s impossible to properly confine it though. While it would therefore generally be advisable to store it wet, but as I didn’t notice any shock or friction sensitivity it was simply kept as the dry crystals shown.


Fig.3-4: Synthesis of disodium azobistetrazolate and carefully evaporating down the final solution


Fig.5-6: The product under the microscope


Fig.7: Crystals of disodium azobistetrazolate pentahydrate

Isocyanogen tetrabromide:
A 100 ml three neck round-bottom-flask, equipped with a Dimroth-condenser, was charged with 0,75 g of elemental bromine (9,4 mmol; made by the oxidation of sodium bromide with potassium persulfate in 95,6% yield), suspended in 20 ml of dest. water. To this, while stirring, a solution of 352,3 mg of disodium azobistetrazolate pentahydrate in 15 ml dest. water was slowly added dropwise, at which point some gas evolution quickly became evident. The mixture was refluxed in a heating block for 3 h, during which time the red bromine color increasingly discolored, and a red oil separated, which eventually “steam-distilled“ into the condenser collecting as a beige solid. The condenser was washed out with DCM, the light yellow reaction mixture extracted more three times, and the pooled extracts washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was removed by rotary evaporation, resulting in a yellowish-green oil, which solidified into a crystalline solid on cooling to room temperature. This crude product is sufficiently pure to be used in the final step of the preparation. 136 mg, 31,3%


Fig.8-9: Synthesis of isocyanogen tetrabromide


Fig.10: the collected crystalline isocyanogen tetrabromide

1-Diazidocarbamoyl-5-azidotetrazole:
In a 10 ml falcon-tube 25 mg of the isocyanogen tetrabromide (67,3 μmol) were dissolved in 0,3 ml of acetone and and the greenish solution cooled to around 0°C with the help of an icebath. The mixture was purged with argon for around a minute, and the tube loosely capped to ensure somewhat inert if an atmosphere. To this 150 μl of a solution of 0,9 g sodium azide in 6 ml dest. water (346,1 μmol), cooled in the same icebath, were slowly added dropwise with occasional swirling of the reaction vessel, and things were then left to stand first for 1 h at 0°C and then 3 h at room temperature. After this 2 ml of dest. water were added to the now orangish solution, and things left to stand in the icebath for 45 min to allow the product to separate. Nothing really happened though until the walls of the tube were very carefully scraped with a plastic pipette, on which a white crystalline solid gradually precipitated. This was removed by gravity filtration, the residue washed with some more water, and the wet white crystals used as such for further experimentation and energetics testing. The footage of those tests can be found in [6].


Fig.11: Synthesis of C2N14


Fig.12-13: The reaction mixture before and after the addition of the water

The 2011 approach by Klapötke [7]:

This approach seems much less accessible on first glance, starting from triaminoguanidine hydrochloride in the original publication. This precursor can actually easily be prepared from widely available guanidine hydrochloride though, and I personally based myself on the procedure given in [8]. This doesn’t just make it a particularly easy approach though, and the key-dimerization (for mechanistic details check out [7]) actually is really pH-sensitive to the extent that tracking the pH with pH-paper doesn’t really suffice [9]. Therefore I may revisit things as soon as I get a proper pH-probe.


Fig.14: The 2011 synthesis of C2N14

Triaminoguanidine hydrochloride:
In a 50 ml round-bottom flask, equipped with a Liebig-condenser, 970 mg of guanidine hydrochloride (10 mmol) were dissolved in 25 ml of warm dioxane and 3,7 ml 100% hydrazine hydrate (75 mmol) quickly added over the course of one minute. The colorless mixture was heated to a reflux in a heating block for 3 h, with some ammonia generation quickly becoming evident (detectable by holding some wet pH-paper over the opening of the condenser), and a white solid starting to precipitate. Things were cooled left to cool down over night, during which time the mixture seemed to have pulled some moisture from the air, so around 10 ml of the solvent were quickly removed by heating on the hotplate, and the precipitated solids removed by vacuum filtration after things had cooled back down again. The residue was washed with some diethylether and acetone, and the very slightly pinkish* crystals dried on the air. 983 mg, 70%
*This discoloration later turned a slight yellow, it can generally be expected to get a completely white product though as this presumably just came from the glassware being contaminated.


Fig.15-16: Synthesis of triaminoguanidine hydrochloride


Fig.17: The collected slightly pinkish crystals of triaminoguanidine hydrochloride

1-Diazidocarbamoyl-5-azidotetrazole (failed attempt):
In a 50 ml falcon-tube 70,5 mg if the triaminoguanidine hydrochloride (0,5 mmol) were dissolved in 7,5 ml of dest. water, and 1 ml of 1 molar hydrochloric acid (1 mmol) was added to the colorless solution. Things were cooled to around 0°C in an icebath, a solution of 69,5 mg of sodium nitrite (1 mmol) in 7,5 ml dest. water was then very slowly added through an addition funnel while magnetically stirring, and the stirring continued for 45 minutes at room temperature afterwards. The pH was very slowly brought to exactly 8* by dropwise addition of 0,1 molar sodium hydroxide solution, during which the previously colorless solution gradually turned a yellow color. Things were extracted three times using 15 ml of diethylether each, by shaking inside the falcon-tube and removing the top layer with the help of a pipette, and the yellow extracts passed through a silica-filled syringe in hopes of removing some amine impurities which would otherwise require the use of a short chloroform column after isolation. The now light yellow extracts were carefully evaporated down in a 50°C water bath while, on which only a tiny quantity of a totally non-energetic yellow oil remained though, why this attempt was discarded.
*This was achieved using pH-paper in this run, what, as mentioned above, isn’t sufficiently precise for this reaction, why this presumably failed.


Fig.18-19: Failed attempt of synthesizing C2N14


Fig.20-21: The mixture before and after the addition of the base


Sources:

[1] https://youtu.be/Hv4Ulb16imk?si=9fL8qJpg2KFjD6S2
[2] https://youtu.be/-Sz4d7RQB6Y?si=Fcq-Es_7Y0mnt1rh
[3] https://patents.google.com/patent/US2990412A/en
[4] https://sciencemadness.org/scipics/Energetic_Derivatives_Of_...
[5] https://youtu.be/_m52RquJi_M?si=7KKYR0Xm8ZWyvvWr
[6] https://youtu.be/Ma-D-cARvXw?si=fsCMM69PBkL09AuV
[7] https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.2011003...
[8] https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002...
[9] https://youtu.be/zUdBHx-F8wQ?si=OXGysXIyVCp9Loo7

Quote: Originally posted by Niklas

The 2011 approach by Klapötke [7]: This approach seems much less accessible on first glance, starting from triaminoguanidine hydrochloride in the original publication. This precursor can actually easily be prepared from widely available guanidine hydrochloride though, and I personally based myself on the procedure given in [8]. This doesn’t just make it a particularly easy approach though, and the key-dimerization (for mechanistic details check out [7]) actually is really pH-sensitive to the extent that tracking the pH with pH-paper doesn’t really suffice [9]. Therefore I may revisit things as soon as I get a proper pH-probe.

To my knowledge there's one other person on the internet, that being ReactiveChem on Youtube, who tried this and he got the same results, probably because of bad temperature control.

I myself actually also tried this exact reaction about a week ago, albeit with lower quality reagents, and it actually worked on the second attempt so here are my two cents on that:

Triaminoguanidinium nitrate was prepared by refluxing 2,44g of guanidine nitrate (20mmol), 9,2g of hydrazine sulfate (70mmol) and 5,7g of sodium hydroxide (140mmol) in 10ml of water for 5h (adapted from [1]). Afterwards while still hot 25ml of cold water with a few drops of conc. HNO3 were added through the condenser. (This serves to acidify the reaction mixture and prevent reactions of free base aminoguanidines with oxygen in the air. This is also likely what caused the pink coloration in your run as oxidation leads to the formation of tetrazine derivatives [2] which are a deep red/purple.) Over the course of a day a bunch of product crystallized at room temperature and more was recovered by fractional crystallization. Yield was 1,7g of of TAG nitrate (67%) which was recrystallized before use.

Now the fun part, C2N14:
For the diazotization 0,33g of triaminoguanidine nitrate (2mmol) and 0,7g of HCl (22-25%, I don't know the actual conc., hardware store grade) were dissolved in 30ml of water and cooled in the freezer. 0,62g or 4mmol of 45% NaNO2 (homemade, the rest is nitrate) was dissolved in 30ml of water and cooled in an ice bath. Once the TAG/HCl solution was semi-frozen the nitrite was added to it with stirring over the course of 20 minutes. During this step the solution was kept in a partially frozen state by occasionally cooling it in an ice/salt bath @-18°C. This makes temperature control way easier. Residual ice was then allowed to melt and after that point stirring was continued for another 30 min. Then 0,1g of ammonium chloride was added and allowed to react for another 10 min. (The idea here is to remove residual nitrite. I figured it can't hurt, no idea if it actually helped though.) The solution was basified by slowly pouring in 0,1M NaOH solution until the pH was a little above 8 (determined using cheap, chinese pH paper). Interestingly during the dimerization/cyclization step I found the pH to decrease again over time so I kept adjusting it to 8 for 5-10 minutes. Then the solution was extraced with three 50ml portions of ether. Evaporation yielded a few tiny droplets of a yellow oil which was highly explosive, detonating even in really small amounts so I'm rather certain it was mostly C2N14. Most likely purer reagents would actually give a crystallizable product or perhaps there's really no way around column chromatography.

That was my second go at it. On the first run I didn't freeze the solution, didn't add any NH4Cl, let the pH drift back without realizing and used ether that wasn't stored over KOH (might've contained some acid). Klapötke et al. wrote that residual nitrite will destroy the azide groups if the pH is too low [3] so that's why i added the ammonium chloride. This might also mean that bringing up the pH too carefully and too slowly could actually degrade the product.

[1] US5041661
[2] The chemistry of aminoguanidine and related substances
[3] C2N14: An Energetic and Highly Sensitive Binary Azidotetrazole

For those who have already prepared DBX-1

Quote: Originally posted by pdb

You know that the synthesis, by evaporating the ketchup-like slurry, produces clumps of an amorphous powder if crystallization isn’t seeded by adding DBX-1 from a previous batch. Under the microscope, this powder looks really messy. Hence my interest in the following publication: https://onlinelibrary.wiley.com/doi/abs/10.1002/prep.2023002... Unfortunately, it’s not available on SciHub. Does anyone happen to have access to it? Thanks in advance!