A DSC study of new compounds based on ( E )-3-(azulen-1-yldiazenyl)-1,2,5-oxadiazole
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A DSC study of new compounds based on (E)‑3‑(azulen‑1‑yldiazenyl)‑1,2,5‑oxadiazole Adina Magdalena Musuc1,3 · Liviu Birzan2 · Mihaela Cristea2 · Domnina Razus1 · Alexandru C. Razus2 · Dumitru Oancea3 Received: 18 October 2019 / Accepted: 4 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Exothermal decomposition of six (E)-(substituted azulen-1-yldiazenyl-1,2,5-oxadiazoles) was investigated by differential scanning calorimetry (DSC) under non-isothermal conditions, in inert atmosphere. From the DSC curves recorded either at various heating rates for three compounds, or at 10 K min−1 for the rest, several physical properties such as the melting temperature, melting heat, temperature and heat of decomposition were evaluated. The activation parameters of the decomposition processes were determined by analyzing their multiple curves, measured at different heating rates, using both the Friedman and Flynn–Wall–Ozawa isoconversional methods and model-fitting methods. The linear dependence of the activation energy on conversion supports the idea of the single-step nature of the decomposition processes for all examined compounds. The decomposition steps were identified from the experimental DSC curves, and their kinetic parameters were evaluated using linear regression methods. New insight into the relationship between melting and structural properties was gained if the equilibrium free energy of melting was splitted into its energetic and entropic components. The resulted thermodynamic and kinetic parameters are used to predict the hazards associated with these compounds. Keywords Azulenyl-diazenyl-1,2,5-oxadiazole · Melting temperature · Melting heat · Melting entropy · Overall activation parameters · Explosion hazards
Introduction The assessment of the thermal stability of condensed compounds under various conditions is important in order to avoid losses during their synthesis, storage, transportation and further use in chemical processes [1–6]. Differential scanning calorimetry (DSC), a technique that requires very Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10973-020-10164-5) contains supplementary material, which is available to authorized users. * Adina Magdalena Musuc [email protected] 1
“Ilie Murgulescu” Institute of Physical Chemistry, Romanian Academy, 202 Spl. Independentei, 060021 Bucharest, Romania
2
Organic Chemistry Center “C. D. Nenitzescu”, Romanian Academy, 202B Spl. Independentei, 060023 Bucharest, Romania
3
Department of Physical Chemistry, University of Bucharest, 4‑12 Regina Elisabeta Blvd, 030018 Bucharest, Romania
small samples and enables rapid and broad temperature range scans, is recommended for such measurements under isothermal or non-isothermal heating regimes. DSC provides data of melting and/or decomposition temperature of explosive compounds, their enthalpy of decomposition and other thermodynamic and kinetic properties [2–8]. The kinetic equations describing decomposition, evaluated from experimental data,
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