Abstract:

The thermal decomposition process of stavudine(STVD) was studied by means of thermogravimetry(TG), differential scanning calorimetry(DSC) and the infrared spectra of STVD. The molecular bond orders were calculated by using GAMESS method of quantum chemistry and the thermal decomposition mechanism of STVD was discussed. The parameters of thermal decomposition kinetics, such as activation energy Ea and preexponential factor A, were obtained by using Ozawa method. The expected lifetimes of STVD at different temperature were estimated using Dakin equation. The results indicated that the thermal decomposition of STVD was a three-stage process. Disconnection of the C—N bond between thymine ring and penta-atomic ring was the first decomposition step. Under nitrogen atmosphere, the temperature range of this first stage is from 139 ℃ to 173 ℃, in which the mass loss is 21.2% while Ea and A are 168.9 kJ/mol and 2.884×1019 min-1, respectively. The second thermal decomposition stage is from 173 ℃ to 313 ℃ with mass loss of 562%, Ea of 96.4 kJ/mol and A of 2.884×108 min-1. The decomposition rate of the third stage is very slow, but still has 10.9% remaining at 800 ℃. When decomposed under air atmosphere, the temperature range, the mass loss, Ea and A are from 139 ℃ to 166 ℃, 19.1%, 168.1 kJ/mol and 2.188×1019 min-1 for the first decomposition stage are from 166 ℃ to 314 ℃, 53.9%, 154.9 kJ/mol and 8.913×1013 min-1 for the second decomposition stage are from 314 ℃ to 550 ℃, 27%, 116.9 kJ/mol and 3.548×108 min-1 for the third decomposition stage. Accordingly, STVD was quite thermally stable under ambient temperature.

Key words: Stavudine (STVD), quantum chemistry, thermal analysis, Mechanism, TG, DSC