Metal ion catalysis in the aminolysis of penicillin

The copper(II) ion catalysed hydrolysis and aminolysis of benzylpenicillin in water at 30° shows saturation kinetics. A 1 : 1 complex is formed between the metal ion and benzylpenicillin which is attacked by hydroxide ion and amine ca. 107-fold faster than unco-ordinated benzylpenicilin. The Brønsted value for nucleophilic attack by amines is 0.87. The copper(II)ion catalysed reactions of the methyl ester of benzylpenicillin show much smaller rate enhancements indicating that the site of co-ordination for the antibiotic involves the ionised carboxy-group. The mechanism of the catalysed reactions does not involve the intermediate formation of benzylpenicillenic acid or a keten. The reactions are inhibited by buffers which co-ordinate to copper(II)ions. Trifluoroethylamine forms a 1 : 1 complex with copper(II) ion with an equilibrium constant of 15.6 l mol–1