Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions |
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Authors: | B Tiţa Eleonora Marian D Tiţa Gabriela Vlase N Doca T Vlase |
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Institution: | (1) Faculty of Pharmacy, ’Victor Babeş’ University of Medicine and Pharmacy, Eftimie Murgu Square, No. 2, 300041 Timişoara, Romania;(2) Faculty of Medicine and Pharmacy, Oradea University, Speciality of Pharmacy, Nicolae Jiga Street, No. 29, Oradea, Romania;(3) Faculty of Chemistry-Biology-Geography, West University of Timişoara, Pestalozzi Street, No. 16, Timişoara, 300115, Romania |
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Abstract: | Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability,
compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process.
The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal
and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG
data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric
kinetics.
In the model-fitting methods the kinetic triplets (f(α), A and E
a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous
work.
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as
well as a different strategy of experimental data processing. |
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Keywords: | diazepine isothermal kinetic study non-isothermal thermal decomposition |
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