The mechanism and kinetics of the thermal decomposition of telbivudine

Abstract

The thermal decomposition of Telbivudine (LdT) was measured with thermogravimetry (TG), differential scanning calorimetry (DSC), and thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TGA–FTIR). The infrared spectra of LdT, its gaseous products, and the remainders of thermal decomposition at various temperatures were determined. The molecular bond orders were calculated by GAMESS program of quantum chemistry, and the mechanism of thermal decomposition of LdT is discussed. The kinetic parameters of thermal decomposition such as activation energy Ea and the pre-exponential factor A were obtained with the Ozawa method. The prospective lifetime of LdT was estimated with the Dakin equation. The results indicated that the thermal decomposition of LdT is a two-step process. Fracture of the peptide bond connecting the thymine and furan rings occurs in the initial step. Under nitrogen atmosphere, the temperature range of decomposition is from 198°C to 314°C, the Ea and A of the thermal decomposition process at the initial stage are 120.9kJmol−1 and 1.66×1011min−1, respectively. In air, the temperature range of decomposition is from 199°C to 309°C, and the corresponding Ea and A are 133.0kJmol−1 and 3.89×1012min−1, respectively. The thermal stability of LdT is very good under routine temperatures.