Thermal behavior and thermal degradation kinetic parameters of triterpene α, β amyrin

Abstract

The pentacyclic triterpenes isomers α amyrin and β amyrin occurs naturally in several plant species, mainly at Burseraceae family. From the oleoresin of its most common species found in the Brazilian Amazon, Protium heptaphyllum, the mixture of α, β amyrin (ABAM) has been isolated and standardized. The aim of this study was to perform thermal analyses together with kinetic parameters of prototype degradation measurements of ABAM obtained from Amazonian commercial oleoresin samples. ABAM was characterized using by chromatographic and spectroscopic methods. X-ray diffraction and scanning electronic microscopy were used to evaluate the crystallinity and surface morphology. The thermoanalytical evaluation was performed through differential scanning calorimetry and thermogravimetry at different heating rates (2.5, 5.0 and 10.0 °C min−1). Fourier transformer infrared spectrometry was used to evaluate the heated samples at different temperatures (100, 150, 175, 200, 225 and 250 °C) in kilns, where the degradation kinetic parameters were evaluated through a variety of methods such as Ozawa, Coats–Redferm, Madhusudanan, Horowitz–Metzger and Van-Krevelen. The results are in accordance with the findings reported in the literature and the kinetic parameters determined by different methods are similar, with a zero-order kinetic and an activation energy of around 75–100 kJ mol−1. The spectral correlation did not show significant changes among the evident bands related to the molecule as the temperature increased, which indicates a thermal stability of ABAM.