A Simplified Approach to Calculating Kinetic Parameters of Thermal Decomposition Processes for Cephalosporin and Penicillin Sodium Salts and to Evaluating their Stabilities

Stefano      Vecchio; Mauro      Tomassetti

Abstract

The thermal stability and thermal decomposition behavior of sodium salts of some penicillins and cephalosporins have been studied using a differential scanning calorimetry technique under a stream of air with a linear heating rate up to 873 K. A “model-free” kinetic method based on the Kissinger equation was applied to decomposition processes of several penicillin and cephalosporin sodium salts to determine activation energy and the pre-exponential factor, following a simplified approach. The values of these parameters referring either to the first or to the slowest decomposition process were used in an attempt to calculate the lifetime for a 1.0% conversion degree of carbenicillin and cephalosporin C, extrapolated at 298.15, 323.15, 373.15 and 423.15 K. Lastly, a comparison of stability data and different calorimetric curve profiles of several antibiotics belonging to the cephalosporin and penicillin classes led to the conclusion that the presence of penicillanic and cephalosporanic rings in all the molecular structures considered does not seem to noticeably affect the overall decomposition mechanisms of the various antibiotics.

Keywords: Activation energy, Cephalosporin salts, Differential scanning calorimetry, Kinetic analysis, Kissinger equation, Penicillin salts, Pre-exponential factor, Storage times, Thermal stability, Kinetic Parameters