Nitrodiazene oxides: a unique nitrogen- and oxygen-containing functional group

Nitrogen-/oxygen-containing functional groups (N/O groups) may be found in a wide variety of areas such as agriculture, drug design and energetic materials. Exploring the chemistry and synthesis of N/O groups is desirable as compounds containing their functionality may prove to be invaluable in a variety of fields. A unique N/O functional group which may offer additional insight into the design of high-heteroatom content systems is the 2-nitrodiazene-1-N-oxide group (NDO group). While unique on their own, NDOs combine the well-known azoxy (N(O)=N) and nitro (-NO2) groups into a single unique N/O functional group. Although NDOs may offer superior densities and enthalpies of formations relative to their nitro counterparts, NDOs have been significantly less investigated than their nitro-bearing counterparts. This work will discuss NDOs in chemical literature from their initial discovery to modern synthesis techniques, energetic properties and chemical stability.

[(3-Nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans: energetic materials containing an N(O)N–N fragment

The strategy for the synthesis of substituted [(3-nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans 4–7, in which the distal nitrogen of the azoxy group is bonded to the nitrogen atom of the azole ring, includes, firstly, the reaction of 1-amino-3-nitro-1H-1,2,4-triazole with 2,2,2-trifluoro-N-(4-nitrosofurazan-3-yl)acetamide in the presence of dibromisocyanuric acid followed by removing of the trifluoroacetyl protecting group to afford aminofurazan (4). Transformation of the amino group in the latter made it possible to synthesize the corresponding nitro (5), azo (6), and methylene dinitramine (7) substituted furazans. The compounds synthesized are thermally stable (decomposition onset temperatures 147–228 °C), exhibit acceptable densities (1.77–1.80 g cm⁻³) and optimal oxygen balance (the oxidizer excess coefficients α = 0.42–0.71). Their standard enthalpies of formation (576–747 kcal kg⁻¹) were determined experimentally by combustion calorimetry and these compounds have been estimated as potential components of solid composite propellants. In terms of the specific impulse level, model solid composite propellant formulations based on nitro and methylene dinitramine substituted furazans 5 and 7 outperform similar formulations based on CL-20 by 1–4 s, and formulations based on HMX and RDX by 5–8 s.

A novel class of energetic compounds with a N(O) N–N fragment, [(3-nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans, which exhibit good thermal stability and high experimental enthalpies of formation are estimated as possible components of solid composite propellants.

Apparent autocatalysis due to liquefaction: thermal decomposition of ammonium 3,4,5-trinitropyrazolate

Thermal decomposition of solids is often accompanied by autocatalysis, one of the possible causes of which is the formation of a liquid phase. The kinetic model considering the liquefaction of solid reactants under isothermal conditions was proposed by Bawn in the 1950s. The present study reports the application of the Bawn model to the thermolysis of 3,4,5-trinitropyrazole ammonium salt (ATNP) under nonisothermal conditions. The thermal decomposition of ATNP is comprised of low-temperature and high-temperature stages. The low-temperature stage exhibits two distinct exothermic peaks in differential scanning calorimetry (DSC), fitted by two consecutive autocatalytic reactions with a model-fitting kinetic analysis. The liquefaction of the solid reactant during the first reaction is directly observed, giving mechanistic evidence for the Bawn model. We have expressed the Bawn model by a combination of two extended Prout-Tompkins (ePT) equations with the activation energy for the leading liquid-state reaction of Ea = 140.6 ± 0.3 kJ mol-1. The release of ammonia is detected from the beginning, suggesting that the thermal dissociation of ATNP to 3,4,5-trinitropyrazole is an initiation reaction of the thermal decomposition. We proposed ATNP liquefication, leading to the apparent autocatalytic behavior of the first global decomposition reaction, is caused by the eutectic formation between ATNP and 3,4,5-trinitropyrazole, as it was confirmed by DSC analysis of the artificial mixture. The presented approach of the combination of ePT formalism with a Bawn model is generally applicable to a broader range of thermal processes accompanied by liquid phase formation and apparent acceleration.

Energetic N-azidomethyl derivatives of polynitro hexaazaisowurtzitanes series: CL-20 analogues having the highest enthalpy

Novel energetic components for rocket propellants, based on polynitro hexaazaisowurtzitanes, have been prepared with high enthalpies of formation that significantly exceed that of CL-20.