238 °C (dec)
FOX-7 is a code name for 1,1-diamino-2,2-dinitroethylene, also called 1,1-diamino-2,2-dinitroethene, and its acronyms can be either DADE or DADNE. FOX-7 is a recent development in the search for insensitive high explosive munitions and is the brainchild of the Swedish Defense Research Agency. While FOX-7 is not more powerful than existing explosives like HMX it is being considered as an effective replacement in certain applications because it is a much safer explosive being quite stable to shock, friction, and heat. It is also an inert chemical with demonstrated compatibility to the usual substances used in explosives. FOX-7 is currently being tested in plastic bonded explosive formulations with energetic binders, in propellant formulations for artillery, and is being considered as a replacement in composition B formulations.
The molecular structure of FOX-7 is actually quite simple considering its performance capabilities. While the chemical precursors to synthesize it have been around for over 150 years, it was only in the mid 90ís that the pieces were put together just right. The precursors required to synthesize FOX-7 are therefore somewhat easy to come by. Getting the two amino groups on an ethene backbone is quite impossible with straightforward synthetic techniques. A more complex nitrogen containing ring is first nitrated, and then the ring is broken forming both of the amines and the double bond of ethane.
|ammonium hydroxide||addition funnel|
|nitric acid||graduated cylinder|
|sulfuric acid||stirring rod/stirrer|
The synthesis of FOX-7 proceeds in 2 stages. The first stage nitrates an imidazole type ring, and the second stage breaks the ring forming the final product, 1,1-diamino-2,2-dinitroethylene.
Preparation of 2,2-dinitromethylene-4,5-imidazolidinedione. Place 198 mL of concentrated sulfuric acid (95% and up) in a 500-mL round bottomed flask and immerse the flask in a salt-ice bath to cool the acid. When the acid has cooled slowly add 35.4 g of 2-methoxy-2-methyl-4,5-imidazolidinedione, which should form a clear yellow solution. Set the flask up for magnetic stirring and attach an addition funnel. Slowly add 43 mL of 70% nitric acid to the flask over a period of 60 minutes while stirring. Keep the temperature of the mixture under 30 °C during the addition. After adding the acid, continue stirring for an additional 30 minutes without any cooling. The solution will change color from yellow, to deep red, and finally to a pale orange precipitate. Pour the contents of the flask over a filter to collect the precipitate and allow it to dry in the open air, or vacuum, at room temperature. Optionally the crystals can be washed with a few small portions of trifluoroacetic acid. This precipitate should be 2-(dinitromethylene)-4,5-imidazoledione in approximately 63% yield.
Preparation of 1,1-diamino-2,2-dinitroethylene. Dissolve the above produced 2-(dinitromethylene)-4,5-imidazoledione in 120 mL of distilled water, with stirring, in a 500-mL flask or beaker. Place the flask in a cold water bath and cool it to below 30 °C. Add 30% ammonium hydroxide to the flask at such a rate as to keep the temperature between 20-30 °C. Add enough ammonium hydroxide to reach a pH of approximately 9. One could also use the weaker 3-4% ammonium hydroxide as found in the grocery store, but much larger quantities will be needed, so use an appropriately sized container. Stir the contents of the flask for 2 hours after adding all of the ammonia. Pour the material over a filter to collect the product. Thoroughly wash these crystals several times with water and allow them to dry under vacuum. What remains are bright yellow crystals of 1,1-diamino-2,2-dinitroethylene, aka FOX-7. Yield of the final product is around 54%.
You will need a graduated cylinder for measuring liquids, a stirring rod or magnetic stirrer for mixing, and a thermometer to monitor the temperature.
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