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Two sides of thermal stability of energetic liquid: Vaporization and decomposition of 3-methylfuroxan
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 Noxide
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 mol1. 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 CAC
and NAO bonds (HNCO, CH3CN), we detect CH3COCN that retains CAC 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.