Mechanism of thermolysis of hydrazino-dinitroethylenes

Ultraviolet-Initiated Decomposition of Solid 1,1-Diamino-2,2-dinitroethylene (FOX-7)

FOX-7 (1,1-diamino-2,2-dinitroethylene) was photolyzed with 202 nm photons to probe reaction energies, leading to the decomposition of this energetic material and to compare results from irradiations using lower-energy 532 and 355 nm photons as well as higher-energy electrons. The photolysis occurred at 5 K to suppress thermal reactions, and the solid samples were monitored using Fourier transform infrared spectroscopy (FTIR), which observed carbon dioxide (CO2), carbon monoxide (CO), cyanide (CN-), and cyanate (OCN-) after irradiation. During warming to 300 K, subliming products were detected using electron-impact quadrupole mass spectrometry (EI-QMS) and photoionization time-of-flight mass spectrometry (PI-ReTOF-MS). Five products were observed in QMS: water (H2O), carbon monoxide (CO), nitric oxide (NO), carbon dioxide (CO2), and cyanogen (NCCN). The ReTOF-MS results showed overlap with electron irradiation products but also included three intermediates for the oxidation of ammonia and nitric oxide: hydroxylamine (NH2OH), nitrosamine (NH2NO), and the largest product at 76 amu with the proposed assignment of hydroxyurea (NH2C(O)NHOH). These results highlight the role of reactive oxygen intermediates and nitro-to-nitrite isomerization as key early reactions that lead to a diverse array of decomposition products.

Electron-Induced Decomposition of Solid 1,1-Diamino-2,2-dinitroethylene (FOX-7) at Cryogenic Temperatures

Solid FOX-7 (1,1-diamino-2,2-dinitroethylene), an energetic material of interest due to its high stability and low shock/thermal sensitivity, was exposed to energetic electrons at 5 K to explore the fundamental mechanisms leading to decomposition products and provide a better understanding of the reaction pathways involved. As a result of the radiation exposure, infrared spectroscopy revealed carbon dioxide (CO₂) and carbon monoxide (CO) trapped in the FOX-7 matrix, while these compounds along with water (H₂O), nitrogen monoxide (NO), and cyanogen (C₂N₂) were detected exploiting quadrupole mass spectrometry both during irradiation and during the warming phase from 5 to 300 K. Photoionization reflectron time-of-flight mass spectrometry detected small molecules such as ammonia (NH₃), nitrogen monoxide (NO), and nitrogen dioxide (NO₂) as well as more complex molecules up to 96 amu. Potential reaction pathways are presented and assignments are discussed. Among the reaction mechanisms, the importance of an initial nitro-to-nitrite isomerization is highlighted by the observed decomposition products.