Catching FOX no. 7 (with pics)

1,1-Diamino-2,2-dinitroethene or FOX-7 is an explosive developed in the late 1990's by the Swedish Defence Research Agency. FOX-7 shows significant improvements in sensitivity compared to RDX, particularly in response to friction and shock.

Molecular formula: C2H4N404
VOD : 8870m/s
Density : 1.88g/cm3
O2 balance : -21.6%
Molar mass : 148.08

I will be using FOI method 2 taken from the pdf file "FOX-7 a new insensitive explosive" by DSTO group.
All reagents were purchased or synthesized to as high standard as possible.
The synthesis is split up into three steps, the following is the first step performed in a half size batch.


REAGENTS

* 430ml methanol (dried with MgSO4 and freshly distilled)
* 116ml 30% Sodium methoxide solution (made with Na metal)
* 18.24g Acetamidine hydrochloride (lab grade)
* 27.92g Diethyl oxalate (collected at still head temp 170-185)
* 200ml dry methanol to dissolve Diethyl oxalate in

2-METHOXY-2-METHYL-4,5-IMIDAZOLIDINEDIONE

A 1 litre three neck flask was charged with 430ml methanol, and 116 ml 30%wt sodium methoxide solution.
18.24g Acetamidine hydrochloride was added and the solution stirred. The flask was fitted with a dropping funnel, drying tube and the final neck was just stoppered. Solution is milky white.

The diethyl oxalate in methanol was added at a slow drip rate over a period of 1.5-1.7 hours and then the reaction mixture was stirred for an additional hour. Solution has changed to light yellow after addition.

The whole reaction mix was dumped into a 2 litre beaker and acidified to ph 4 by the addition of 35% concentrated hydrochloric acid and ph test strips. Temperature did not rise much at all during this step.

The solution was double filtered with a vacuum pump and buchner and the solution (now clear) placed in a pyrex oven dish to evaporate. The paper says the temperature of evaporation must not be above 30C which means nearly 750ml of methanol plus a small amount of water must be evaporated at room temperature .
Will update upon recovery of the solid product.















[Edited on 6-7-2018 by greenlight]

[Edited on 6-7-2018 by greenlight]

[Edited on 7-7-2018 by greenlight]

Quote: Originally posted by Hunterman2244

Sounds fun, if I could find a route to the reagents I would love to try it.

Quote: Originally posted by joseph6355

Quote: Originally posted by Hunterman2244   Sounds fun, if I could find a route to the reagents I would love to try it. 2-METHOXY-2-METHYL-4,5-IMIDAZOLIDINEDIONE is one of them.

The biggest problem with this method both on an amateur scale and a commercial level is the first 2-methoxy-2-methyl-4,5-imidazolidinedione step.

The reagents are hard for an amateur to find but the rest of the synthesis just requires easy to get acids and ammonia solution.
The other problem is the amount of solvent used. In the paper, the author uses over 1.5 litres of methanol to yield just under 20 grams of FOX-7. Using less solvent significantly lowers yields so on an industrial scale the reactors would have to be huge and not to mention the quantities of dry methanol needed.

On a brighter note all 750ml of methanol has nearly evaporated and the solid has crystallized out on top of the small amount of water remaining from the HCl addition. Soon I can recrystallize to get rid of the sodium chloride impurities before nitration.

[Edited on 9-7-2018 by greenlight]



[Edited on 9-7-2018 by greenlight]

Ooh I don't have a short path condenser yet, must put it on the list.

I just finished drying the recrystallized product. There is an unusual error in the paper where it says the solid was dissolved in 320ml methanol, insoluble salts removed, and then the volume was reduced to 320ml?!?! before placing in a refrigerator.

Well I dissolved my 28g of solid in 160ml of boiling methanol because it's a half size batch and stirred for a few minutes, hot filtered, and the reduced it to about 1/3 of the initial volume. Then I placed it in a freezer overnight and filtered the next day.
I have 9-10g of insoluble crap and 14g of the intermediate product. This corresponds to only a 53% yield compared to the papers 64%
I have lost about 4 or 5 grams, but nevertheless, I will perform the nitration and alter the acid amounts accordingly to the loss of product.

Thanks Tdep

Looking over the next step it involves filtering a concentrated mixture of acids at the end with no water dilution like most He's. That shit eats straight through my filter papers,I just did a test with mixed acids.

I am going to have to order a better filtering funnel, maybe fritted glass for the next step before I proceed.

Quick update on the FOX-7.
While waiting for my glass funnel, I had an "it will be fine, I will separate it" moment and performed the nitration anyway. It ran perfectly smoothly and due to having no proper filter I crudely tried to scoop out the fine light yellow crystalline product.
I managed to get most of it out and lay it out to dry but it was still too wet and by the next day the residual sulphuric acid had sucked so much moisture out of the air it was a wet mess and there was barely any crystals left.

I have just written to say I have more oxalic acid on the way to make fresh diethyl oxalate and I will be running it again from the start as soon as I can, so no I have not given up on this synthesis just taken a few steps back.
Just to make it worse my funnel arrived the next day

I have just re-run the first step but this time I bubbled dry HCl gas through the stirred solution to acidify it. No pesky water this time
Now to wait for the methanol to evaporate again.

[Edited on 17-8-2018 by greenlight]

[Edited on 17-8-2018 by greenlight]

Finally had time to do the nitration of the 2-methoxy-2-methyl-4,5-imidazolidinedione. This time I yielded 14,95 grams which equates to about 55.5% yield, slightly more than last time. I recalculated the amounts of acids for my amount of intermediate product.

REAGENTS

* 14.95g 2-methoxy-2-methyl-4,5-imidazolidinedione
* 83.66ml 98% Sulfuric acid
* 18.11ml 70% Nitric acid

2-2-DINITROMETHYLENE-4,5-IMIDAZOLIDINEDIONE

The 1 litre 3 neck flask was fitted with a dropping funnel, CaCl2 filled drying tube and thermometer and placed in an ice bath on top of a hotplate with stirrer.

83.66ml of 98% sulfuric acid was added and chilled down to about 10 degrees C. The 2-methoxy-2-methyl-4,5-imidazolidinedione was added in small portions with the stirrer on. No temperature rise was noted during the additions. Everything dissolved and formed a clear but yellow solution.

The dropping funnel was filled with 18.11ml 70% nitric acid and the addition was started with the stirred solution at 5 degrees C. After the first few additions dropwise, the colour changed to a dark red wine texture. I never let the temperature rise above 12 degrees just to be safe (paper states 30C). When almost all the nitric acid was added, the mixture all of a sudden went hot pick and crytals precipitated almost instantly. Quite a pretty sight The colour quickly faded to orange and then beige as the last of the acid was added.

The flask was taken out of the ice bath and stirred at room temperature for 30 minutes before filtering through a fritted filter this time. I still lost a decent amount of product as it is so fine that a lot of it passed through the frit. What was collected is currently drying further in a desiccator over anhydrous calcium chloride. I am not sure this is going to work but I do not want to risk it turning to a puddle drying in the open because it is damp with hygroscopic acid. I wish there was a solvent it could be washed with before drying it.




[Edited on 5-9-2018 by greenlight]

[Edited on 5-9-2018 by greenlight]

On the paper it just says air dried but I am sure it will just get even wetter in air. I have it in the desiccator and it has not dried one bit more.

You might be on to something there about washing with nitric. I think I will just run the final step with it damp because it is getting put into water anyway.

This stuff takes the cake for most annoying to filter and dry. Imagine making PETN for example and not dumping it into water before filtering but instead trying to filter and process it straight from the nitration bath Not fun

[Edited on 5-9-2018 by greenlight]

The nitrated intermediate is still damp after 12 hours in a desiccator so I proceeded with the final hydrolysis step.

REAGENTS

* 30% w/w ammonia solution

1,1-DIAMINO-2,2-DINITROETHENE (FOX-7)

The damp nitrated intermediate from step 2 was added to 50ml distilled water in a 250ml conical flask and the suspension set on stir.
30% ammonia solution was added dropwise while maintaining the temperature between 20-30 degrees C.

With each addition, a gold colour was noticed where the ammonia solution contacted the suspension. A small exotherm with frothing was noticed about halfway through and the temperature jumped to 31 degrees C momentarily but quickly cooled back down.
The pH was monitored with test strips and addition was stopped at approximately pH 9. Fine canary yellow crystals of 1,1-diamino-2,2-dinitroethene were now suspended in the solution.

The solution was stirred for 2 hours and then filtered before washing with water a few times. The yield is nearly dry and reads 4.5 grams on the scale which is half of what is claimed on the paper even when taking into account a half sized batch. Paper mentions 19.66g final yield which means I should have around 9.5g.
I attribute this to not getting a full yield of 2-methoxy-2-methyl-4,5-imidazolidinedione and then losing a lot of the nitrated intermediate when trying to filter again (did I mention it is shit to filter. Also not having the intermediate dried properly may have had an effect.

I have another last batch of 2-methoxy-2-methyl-4,5-imidazolidinedione which I can process and try and get some more for testing purposes.

The disadvantage with this synthesis is definitely the large amount of solvent and exotic reagents needed, and the three steps for a small amount of product returned. Even if you get a decent yield from the half sized batch, it would only be just over 9 grams.


[Edited on 6-9-2018 by greenlight]



[Edited on 6-9-2018 by greenlight]

[Edited on 6-9-2018 by greenlight]

[Edited on 6-9-2018 by greenlight]

@HNA, thanks. I am sure if (di) diazodinitroethene was possible it would have been attempted by someone by now. I am guessing that it would lose its favorable stable properties though by chucking those diazo groups on if it is possible but I doubt that.

@Tdep, Yes that is the colour its meant to be, I asked myself the same question. From high density energy materials:

"FOX-7 exists as a canary-yellow solid and may be recrystallized from various solvents"

It is the kind of picric acid colour that makes you not want it to contact anything in your lab but I have found it doesn't stain anything at all except the filter paper and easily washes off instruments and skin. It is a well behaved yellow

Thanks NP
I am not sure if I will recrystallise it yet. Apparently it can be done with DMSO or 0.5, HCl but it has limited solubility in the dilute HCl.

I think for testing purposes, I could press it in a aluminium tube with an initiating charge of lead azide on top and detonate it against a steel plate. I would also make a second charge of PETN pressed the same in the same type of tube to compare it with.

PETN vs FOX-7

I decided to test the FOX-7 against a known energetic and using NP's idea I used PETN.

I took 3.5 g of each explosive and pressed them hand tight in a bench vice into 12mm diameter aluminium tubes. Unfortuneately I don't have a device for measuring the amount of pressure put into loading each one. They were both as tight as I could get with my hand.

300mg lead azide was then packed carefully on top of each secondary to absolutely ensure initiation. Finally a small amount of Black powder and a piece of visco before sealing them.
The charges were taped onto small matching 3.4mm thick steel plates I had laying around as shown below:



Full detonations were observed on both plates. The results are quite interesting as the PETN created a deeper dent of 9mm depth while the FOX-7 produced only a 7mm deep indent.



I held the plates level and filled the dents with water multiple times, measuring the amount held and averaged the results and the PETN plate lost....wait what the fuck!?? No it didn't, the FOX-7 plate holds just as much and slightly more water (43.25ml) than the PETN witness plate (43.10ml). The FOX-7 dent is wider though.

The PETN charge threw the plate nearly twice as far as the FOX-7 did as well.

My conclusion is that the PETN is more brisant than the FOX-7 and creates a deeper dent and projects the plate farther but the FOX-7 still has nearly equal power as the dent is much similar and does indeed hold more water.

The PETN definitely does have more brisance and shattering power though and it is known to perform better than some explosives in smaller charges. All that work to find th

The FOX-7 takes the win in the stability insensitivity and heat resistance (due to the amine groups) though and that seems the current trend nowadays in energetics; but damn that stuff is a costly time consuming fucker to make











[Edited on 2-10-2018 by greenlight]




[Edited on 2-10-2018 by greenlight]

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I also have these two photos of the plates that show the two dents are extremely similar in shape and size:





I have been trying to explain why the PETN dent is deeper slightly though. Both explosives have similar negative oxygen balances. PETN is -10.21 and FOX-7 slightly more negative at 21.6% exactly the same as RDX. Not enough to really make a difference there.

When I calculate the moles of gas produced upon detonation though the results are more interesting.
PETN (C5H8N4O12) produces 14 mol gas whether you favor CO or CO2 in the products.
FOX-7 (C2H4N4O4) produces only 6 mol of gas upon detonation.
If you work out how much gas is evolved per gram of explosive you get these numbers:

PETN = 0.992L has per gram
FOX-7 = 0.908L gas per gram

I think the excess 0.084L of gas produced exerts slightly more pressure on the surroundings (thin steel plate) and causes the PETN to get the higher result in the plate dent test.

I think the FOX-7 would work well in shaped charges, especially EFP's, as from experience PETN seems to have an easy to cross upper limit where it starts to rip the liner into pieces instead of form a slug. Ideally, you could use more FOX-7 explosive to get a high velocity on the slug before you reached this limit. This is just my opinion I do not know how much truth would be in this.

I really need more FOX-7 to conduct different tests but damn it's expensive to make at home



[Edited on 5-10-2018 by greenlight]



[Edited on 5-10-2018 by greenlight]

I would guess that they seem similar in power because they're at similar density, but if you were to bring them close to their max density the FOX-7 would be all around more powerful.
Even though FOX-7 has a higher max density compared to PETN that doesn't necessarily mean it reaches a higher density when pressed with equal force, a lot of that comes down to crystal size I think.

In any case this is an awesome thread!

@OneEyedPyro, ..I have seen arbor presses before and I have one on my list of things to get as I was going to use it to press AP and whistle rockets too.

Your idea of measuring the volume of the tubes is good. I use a similar technique when getting a density value for plastic explosives by pressing a small amount in a syringe and calculating density from the ml and grams.

What does attaching the torque wrench to the arbor press do. I have seen modified arbor presses like that on pyrotechnic sites. Does it enable me to know how much pressure I am applying.

The secondaries are quite low risk to press (PETN borderline out of them all) but I do use shielding just in case.
Pressing primaries into caps is the task that always gets me on edge though