Alternatives for a phosgene-free synthesis of Akardite II

Abstract. With the high instability of nitric esters used as propellants, it is imperative the use of stabilizers that can prevent the autocatalytic decomposition of the energetic material. Even that alternative stabilizers are being investigated, currently, at the industrial level, nitric ester-based propellants are still stabilized using aromatic amines, such as diphenylamine (DPA) or urea derivatives such ethyl centralite (EC) or Akardite-II (AK-II). The synthesis of urea-based stabilizers involves highly toxic starting materials (phosgene and its derivatives and alkyl isocyanates). Some of these stabilizers are either toxic by themselves, or produce carcinogenic nitrosamines as they scavenge NOx radicals. Although nitrosamines are among the reaction products of AK-II, these nitrosamines are less carcinogenic and produced in lower amounts than the ones produced by the other NC stabilizing additives. Using symmetrical substrates such as nitroaromatic carbonates, urea, and carbonyldiimidazole, in combination with diphenylamine and methylamine, a phosgene-free catalytic synthesis of AK-II is being proposed and under study. The reaction is catalysed either by iron species or imidazolium salts. Iron species are reported to be excellent catalysts for the formation of C-N bonds , and the imidazolium salts can promote the activation of the substrates containing C=O groups that facilitate the C-N bond formation.