Authors:Fabiana Felix, L. Cides da Silva, L. Angnes, and J. Matos
The thermal decomposition of salbutamol (β2 — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry
(TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by
the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy
was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage
of the thermal decomposition process. For isothermal experiments the average values were Eact=130 kJ mol−1 (for standard sample) and Eact=252 kJ mol−1 (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min−1). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min−1). The calculated values were Eact=134 kJ mol−1 (for standard sample) and Eact=139 kJ mol−1 (for pharmaceutical sample).
The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this
work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method.
From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different
structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic
phase, the mean value of the activation energy of 146.3 kJ mol–1, and the pre-exponential factor of 3.43⋅1014 min–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation
energy of153.3 kJ mol–1, and the pre-exponential factor of 4.11⋅1014 min–1 are obtained.
Via the Piloyan method, activation energiesE were determined for polynitroaromatic compounds containing two picryl groups, and for melamine derivatives. At the same time the initial temperatures of exothermic decompositionTD were determined by means of non-isothermal DTA. Linear relationship were derived betweenE ·TD−1 and published kinetic data obtained from the study of HNB, HNAB, DIPS, DIPSO, HNS and TPM by isothermal manometry. On the basis of the derived relationship, as well asE andTD values from DTA measurements, kinetic data were calculated for DPA, KDPA, DMHNB, DPM, DPE and TMPM with the manometric method.