Effects of alkyl chains on the physicochemical properties of nitroguanidine derivatives

Propyl nitroguanidine (PrNQ) is an important nitroguanidine (NQ) derivative and is considered to be promising as a melt-cast carrier explosive (melting point: 98–99 ​°C) due to its low cost, low sensitivity, and good compatibility. However, the effects of alkyl chains on the physicochemical properties of nitroguanidine derivatives have not been well established. In this work, we investigated the physicochemical properties of three structurally similar nitroguanidine derivatives in detail, namely, propyl nitroguanidine (PrNQ), propargyl nitroguanidine (PraNQ), and isopropyl nitroguanidine (IPrNQ). These different three-carbon alkyl group substituents cause these nitroguanidine derivatives to form different crystal structures and intermolecular interactions (hydrogen bonds and van der Waals interactions), which in turn result in significantly different densities, melting points, decomposition temperatures, and detonation properties. These results demonstrate the important influence of the alkyl chain on the physicochemical properties of nitroguanidine derivatives and provide guidance for designing new alkyl-substituted energetic materials, especially for melt-cast explosives.