The effect of the chemical character of certain penicillins on the resistance of the beta-lactam group in their molecules. Part 5: Kinetics of thermal decomposition in solid state.

The decomposition rate at elevated temperature was studied of the following penicillins: ampicillin trihydrate (1), 6-aminopenicillanic acid (2; 6-APA), amoxicillin trihydrate (3), piperacillin (4), amoxicillin sodium (5), azlocillin sodium (6), mezlocillin sodium monohydrate (7) and azidocillin sodium (8). The pattern of decomposition was found to comply with the first-order reaction. The thermal stability of the compounds at 25 degrees C increased in accordance with the sequence 1 less than 2 less than 3 much less than 6 less than 5 less than 8 less then 7 much less than 4, which was connected with the hydrophilic and lipophilic properties of these penicillins. An isokinetic enthalpy-entrophy correlation was demonstrated. The calculated beta value was 420 K.