I was reading that carbon subnitride or Dicyanoacetylene has one of the hottest flames when used as a fuel, but it also is unstable and can explode easily into carbon powder (no specifics on cause). The only thing I know about its production is that it requires extremely hot graphite to have nitrogen blown on it. What specific risks are there in producing it or storing it, and how does it get produced and stored safely? For example is it safe to store at room temperature? Can it be produced safely in a normal atmospheric environment?
I suspect that it will be difficult to make, but it will be a very endothermic compound. As a result it has the potential to decompose back into the elements with a release of heat energy.
If we assume that when C4N2 is a gas, then if it decomposes it will form N2 and four carbon atoms. As the number of moles of gas does not increase at STP, the explosive power of the substance (product of heat of detonation multipled by the increase of number of moles of gas) will not be very large for a given heat release.
If we look at the literature, (Moureu, C. and Bongrand, J. C., Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences1910vol. 150p. 225 - 229) it indicates the melting point of the compound is 21 oC and the boiling point is about 76 oC. Thus it will have a high vapour preassure. Thus we can consider it to be a volatile compound.
Sadly I have been unable to find any details of the thermochemistry of this compound.
There is no way, dicyanoacetylene can be produced at room temperature. According to the paper "Syntheses of Dicyanoacetylene", decomposing 4,5-dicy ano-1,3-dithiol-2-one at 600-800°C, a 59-76% yield of dicyanoacetylene is obtained along with side-products like carbon disulfide, carbonyl sulfide and sulfur. Another scheme is pyrolyzing solid dicyanodiazomethane at 220°C, which polymerizes. The polymerised product is decomposed at 700°C to get desired product. Further, a note on the storage of dicyanoacetylene is mentioned:
Dicyanoacetylene is a hazardous material. Because of its toxicity and high vapor pressure at room temperature, it should be handled only in a hood. It is potentially explosive, both in the pure state and in concentrated solutions, but its thermal stability in dilute solutions in inert solvents is greater than previously re-ported. Pure dicyanoacetylene turns dark slowly at room temperature, but it can be kept almost indefinitely at Dry Ice temperature.
Dicyanoacetylene can only be kept at very low temperatures, in dry ice or liquid nitrogen, like a dewar, away from light and oxygen, as it may polymerize. Do not store it for long. Diluted solutions of dicyanoacetylene are much more stable, and can be safely kept at standard conditions.
- J. Org. Chem., 1968, 33 (2), pp 541–544 DOI: 10.1021/jo01266a014