DEGRADATION KINETICS OF A NEW CEPHALOSPORIN DERIVATIVE IN AQUEOUS-SOLUTION

The degradation kinetics of a new cephalosporin derivative (I) in aqueous solution were investigated at 60°, μ = 0.5, at pH 2.0‐10.0. The observed degradation rates followed pseudo‐first‐order kinetics and were influenced significantly by H2O and OH− catalysis. No primary salt effect was observed in the acid region, but a positive salt effect was observed at pH 9.4. A general base catalytic effect by a phosphate buffer species was observed at pH 7‐8. The pH‐rate profile for I exhibited a degradation minimum at pH 6.05. The Arrhenius activation energies determined at pH 4.0 and 9.4 were 27.2 and 24.5 kcal/mole, respectively. Excellent agreement between the theoretical pH‐rate profile and the experimental data supported the hypothesized degradation process. A comparison of I and cefazolin revealed close structural and stability analogies. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company