Kinetics of ambuphylline decomposition studied by the incremental isoconversional method

Ambuphylline is a drug obtained by the combination of theophylline and 2-amino-2-methyl-1-propanol. Thermal decomposition of ambuphylline was studied using thermogravimetry and differential scanning calorimetry. Under thermal decomposition, ambuphylline exhibits two degradation steps that are clearly separated. In this paper, the kinetic analysis of the first decomposition step has been carried out by employing the incremental isoconversional method for kinetic analysis based on the orthogonal distance regression. The kinetic parameters of the Arrhenius and Berthelot-Hood temperature functions were evaluated. The results obtained show that the ambuphylline degradation exhibits an induction period for temperatures close to the ambient one. After finishing the induction period, the decomposition proceeds rapidly.