Degradation of ampicillin in the presence of cadmium(II) ions

Cadmium (II) ion-catalyzed degradation of ampicillin in methanol at 20 degrees C has been studied. It has been observed that the rate values tend to saturate when the concentration of ampicillin or the metal ion is increased. The results obtained in the present study suggest that ampicillin degradation occurs through the formation of a 1:1 (SM) and 2:1 (S2M) ampicillin-metal complexes. These complexes decompose giving a single product (absorption maximum at 285 nm; (epsilon(p) = 1.82 x 10(4) l mol(-1) cm(-1)) that has been isolated and identified (Cd-II (L2-)(2) (H2O)(4) Na-2). The appearance of this product reflects a first order reaction with respect to the 1:1 complex, with a rate constant of 3.87 x 10(-2) min(-1) and the existence of an equilibrium between the 1:1 and 2:1 initial complexes. The equilibrium constant value, calculated from kinetic data, is 1.7 x 10(3) l mol(-1). (C) 1998 Elsevier Science B.V. All rights reserved.