Explosives, or high energy density materials (HEDMs), need to combine a good explosive performance with a low sensitivity to impact or friction. Finding a compromise between performance and safety can be challenging. RDX (cyclotrimethylenetrinitramine) is a widely used and comparatively stable explosive. It is particularly important for military applications. Finding a less sensitive alternative to RDX could improve the safety for users.
Ralf Haiges and colleagues, University of Southern California, Los Angeles, USA, have synthesized five [C(NO2)3]− (nitroformate) salts with nitrogen-rich cations for use as explosives. The team synthesized HC(NO2)3 (nitroform) by adding concentrated nitric acid to a solution of 4,6-dihydroxypyrimidine in concentrated sulfuric acid. The desired salts were then synthesized by adding different nitrogen-containing bases (methylamine, dimethylamine, ethylenediamine, methylhydrazine, or formamidine) to the nitroform.
The team determined the crystal structures and explosive properties of all five synthesized salts using single-crystal X-ray analysis, differential thermal analysis, and friction and impact sensitivity measurements. Formamidinium nitroformate, [CH(NH2)2]+[C(NO2)3]−, has the best performance as a HEDM. It slightly outperforms RDX and is less sensitive to impact and friction, which makes it a promising explosive. According to the researchers, the low sensitivity can be attributed to the salt’s crystal structure. It features orderly stacked planar layers, which can slide against each other and, thus, absorb mechanical energy.
- Formamidinium Nitroformate: An Insensitive RDX Alternative,
Amanda F. Baxter, Igor Martin, Karl O. Christe, Ralf Haiges,
J. Am. Chem. Soc. 2018.