Two sides of thermal stability of energetic liquid: Vaporization and decomposition of 3-methylfuroxan

• Published in: Journal of molecular liquids 2022-02, Vol.348, p.118059, Article 118059
• Main Authors: Muravyev, Nikita V., Melnikov, Igor N, Chaplygin, Daniil A., Fershtat, Leonid L., Monogarov, Konstantin A.
• Format: Article
• Language: English
• Subjects: Activation energy; Calorimetry; Evaporation; Furoxan; Kinetic analysis; Thermal stability
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2021.118059

[Display omitted] •Thermal transformations of 3-methylfuroxan include isomerization, vaporization and decomposition.•Pressure DSC allows observing autocatalytic thermolysis of MMF.•Kinetic parameters for thermolysis in solution are equal to that for unsubstituted furoxan.•Ring opening mechanism is suggested to explain the detected by GC–MS gas products. Analysis of thermal behavior of liquids is often accompanied by vaporization. In an extreme case, the calorimetric (DSC) experiment reveals the only endothermic evaporation instead of the more valuable thermal decomposition. 3-Methylfuroxan (MMF) is an energetic monosubstituted 1,2,5-oxadiazole N-oxide that shows the above behavior. We investigate the sample mass and confinement effects and show that the pressure DSC allows observing thermal decomposition of target compound at 2.0 MPa. Advanced model-fitting kinetic analysis reveals two global stages, the first of which is a competition between the noncatalytic reaction and autocatalytic one, whereas the second global stage is a second-order reaction. Analysis of MMF thermolysis in solution in dibutyl phthalate shows the activation energy for noncatalytic reaction to be 145.4 ± 1.7 kJ mol−1. To resolve the gas decomposition products in experiments at 0.1 MPa pressure, where the evaporation is abundant, a gas chromatography–mass spectrometry coupled with thermal analyzer was used. Among the gases that are consistent with a furoxan ring rupture by CC and NO bonds (HNCO, CH3CN), we detect CH3COCN that retains CC bond. The formation of geminal cyanonitro compound in the course of thermolysis is proposed to explain the composition of the gas reaction products. Overall, with the range of thermal analysis tools (DSC, PDSC, GC–MS/TGA, thermokinetic modeling) we performed a detailed analysis of thermal transformations of unexplored simple monosubstituted furoxan. The applied methodological approaches could be transferred to other molecular liquids.