Chisholm
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Problem: FOX-7 runaway
I recently acquired 500 grams of 2-methylimidazole, and decided to try my hand at synthesizing a compound more recent than the New Deal.
What I did (footnotes marked with asterisks):
I measured out 20 grams of 2-MIZ in a 1-L beaker and added 200mL of 98% sulfuric acid that had been stored in the freezer. Since I wanted to try
dissolving the 2-MIZ in the minimal amount of acid possible, I first added ~30mL of the acid to the imidazole. There was a significant plume of white
imidazole-smelling vapor. I gave up on moderation and decided to add the entire 200 mL of acid immediately.
It took about two to five minutes for the entirety of the 2-MIZ to dissolve. The temperature rose to 30-ish Celsius. A cold-water bath with a little
ice was used to bring the temperature back down to 15ºC.
I measured out 50mL of azeotropic (67.2%) nitric acid (stored in the freezer) into an addition funnel and added 20 grams of powdered ammonium nitrate,
expecting most of it to dissolve. It did not, but it didn't plug the stopcock, so I commenced with the addition.
The Swedish paper stated that the addition took place at 15-20ºC, so I used a cold water bath with minimal ice to keep the temperature within this
range during addition, despite obviously being able to go much much lower. There were a few excursions into 20-25ºC territory, but these never lasted
more than a few seconds, since I would add ice to the bath, stop addition and stirring, and swirl the beaker until it returned to 15ºC.
After a bit of addition, the color changed to a distinctly more yellow hue than the initial 2-MIZ sulfate solution and I noticed what looked either
like tiny specks of precipitation or tiny gas bubbles. There was no hint of NOx formation.
While there was still a portion of nitric acid in the funnel, I added about 30mL of cold sulfuric acid to the addition funnel and stirred to dissolve
the ammonium nitrate. I took a temperature reading of the inside of the funnel, and it was about 30ºC.
Since a good portion of the heat increase from addition came from the water in the azeotropic nitric acid reacting with the sulfuric acid, I figured
that I would simply perform the addition more slowly, and watch the temperature very carefully.
As addition continued, the color changed to a brownish-purple. I continued addition in the 15-20ºC range, and at a certain point a noticeable
quantity of nitrogen dioxide evolved. Since I knew that one of the intermediates had a gem-dinitro group that liberated NO2 on standing, I didn't go
into panic mode as I would with most any other nitration.
I opened a container of 25% ammonia water and wafted some of the vapor into the beaker in an attempt to destroy the NO2. This seemed to work, but the
resulting white mist made it impossible to read the thermometer, so I closed the ammonia container, picked up the beaker, walked several paces away,
and waved my hand over the beaker to disperse the white mist. I then returned the beaker to the bath, checked the temperature, cooled to 15º, and
continued addition. The solution turned red, and bubbling began. I checked the thermometer and saw it had reached 30, then 40, then 50, 60, 70
degrees. I took the beaker outside, laid it on the ground, and stepped away. The fumes coming off were mostly white, though with a little NO2 mixed
in.
At the precise instant I realized I had left the thermometer in the beaker, I heard a crack, and upon removing the thermometer, the bulb had
shattered. The solution had reached a temperature of at least 130ºC. It had turned completely black. After 10 minutes or so, I poured 800mL of water
into the beaker before dumping it. The brown-black product seemed entirely soluble in water.
So, what happened? What should I do differently next time?
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PHILOU Zrealone
International Hazard
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I think the use of azeotropic HNO3 is counter productive....
The runnaway comes from hydrolysis of of trinitro or tetranitro MIA...
FOX-7 an new insensitive HE synthetic pathways
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Microtek
National Hazard
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Also, I think adding the methylimidazole to the sulfuric acid (slowly, with stirring) is better than doing it the other way round.
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Chisholm
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The thing is, the initial Swedish paper describing the imidazole route used 92% sulfuric acid rather than 98%. The reason I tried using an ammonium
nitrate solution of HNO3 rather than plain HNO3 was to ultimately match the water content of a 92% sulfuric acid mixture by the end of the addition.
If plain ammonium nitrate would be superior, I'd try it. I'm just worried about the heat given off by the cation exchange, as well as the solubility.
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PHILOU Zrealone
International Hazard
Posts: 2893
Registered: 20-5-2002
Location: Brussel
Member Is Offline
Mood: Bis-diazo-dinitro-hydroquinonic
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The hydrolysis of the unstable molecule will yield HNO2 and NxOy what are uncompatible with NH4(+)...
NH4NO2 is hell unstable HE...
So...
NH4NO2 --> N2 + 2 H2O + lot of heat
H2SO4 + H2O --> lot of heat
So changing the initial set of reaction conditions by adding a single ingredient that seems armless...turns a dangerous reaction into a runaway one
EVEN MORE DANGEROUS.
Better use LiNO3, NaNO3, Mg(NO3)2...but keep in mind that FOX-7 is very stable but not the intermediary compounds...so never make large
batches....EVER.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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