鬼臼毒素及其衍生物热分解反应的动力学研究

The thermal behavior and thermal decomposition kinetic parameters of podophyllotoxin （1） and 4 derivatives, picropodophyllin （2）, deoxypodophyllotoxin （3）, fl-apopicropodophyllin （4）, podophyllotoxone （5） in a temperature-programmed mode have been investigated by means of DSC and TG-DTG. The kinetic model functions in differential and integral forms of the thermal decomposition reactions mentioned above for first stage were established. The kinetic parameters of the apparent activation energy Ea and per-exponential factor A were obtained from analy- sis of the TG-DTG curves by integral and differential methods. The most probable kinetic model function of the decomposition reaction in differential form was （1- a）^2 for compounds 1-3,2/3·a^-1/2 for compound 4 and 1/2（1-a）·[-In（1-a）]^-1 for compound 5. The values of Ea indicated that the reactivity of compounds 1-5was increased in the order： 5〈4〈2〈1〈3. The values of the entropy of activation △S^≠, enthalpy of activation △H^≠ and free energy of activation △G^≠ of the reactions were estimated. The values of △G^≠ indicated that the thermal stability of compounds 1-3 with the samef（a） was increased in the order： 2〈3〈1.

Kinetic Investigation of Thermal Decomposition Reactions of Podophyllotoxin and Its Derivatives

The thermal behavior and thermal decomposition kinetic parameters of podophyllotoxin ( 1 ) and 4 derivatives, picropodophyllin ( 2 ), deoxypodophyllotoxin ( 3 ), β‐apopicropodophyllin ( 4 ), podophyllotoxone ( 5 ) in a temperature‐programmed mode have been investigated by means of DSC and TG‐DTG. The kinetic model functions in differential and integral forms of the thermal decomposition reactions mentioned above for first stage were established. The kinetic parameters of the apparent activation energy E_a and per‐exponential factor A were obtained from analysis of the TG‐DTG curves by integral and differential methods. The most probable kinetic model function of the decomposition reaction in differential form was (1?α)² for compounds 1 – 3 , (2/3)·α^?1/2 for compound 4 and (1/2)(1?α)·[?ln (1?α)]^?1 for compound 5 . The values of E_a indicated that the reactivity of compounds 1 – 5 was increased in the order: 5 < 4 < 2 < 1 < 3 . The values of the entropy of activation ΔS^≠, enthalpy of activation ΔH^≠ and free energy of activation ΔG^≠of the reactions were estimated. The values of ΔG^≠indicated that the thermal stability of compounds 1 – 3 with the same f(α) was increased in the order: 2 < 3 < 1 .