Thermal Decomposition of Some Benzodiazepines under Non-Isothermal Conditions Kinetic Study

Thermal analysis is a routine method for the analysis of drugs and substances of pharmacological interest. Kinetic studies have become a crucial point in thermal analysis, in which the main purpose is to determine the mechanism(s) of decomposition and to calculate the parameters of the Arrhenius equation. The results are further used to predict the system's behaviour in various circumstances. The diazepam's, nitrazepam's and oxazepam's thermal decomposition kinetics has been studied under non-isothermal conditions, using 5, 7,10,12 and 15 degrees C min(-1) heating rates and a nitrogen dynamic atmosphere. The methods used for TG/DTG data processing have been those of Friedman, Flynn-Wall-Ozawa, Kissinger and respectively Nomen-Sempere. The decomposition process has been relatively complex for a simple and easy correlation of the kinetic data with the molecular structure's characteristics. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing. Only the non parametric method of Nomen and Sempere was able to provide a less speculative comment.