METAL ION CATALYSIS OF ANHYDRIDE HYDROLYSIS. METAL ION PROMOTED WATER AND HYDROXIDE ION CATALYZED REACTIONS OF MIXED CINNAMIC ACID ANHYDRIDES.

Article abstract of DOI:10.1021/ja00344a036

Rate constants have been determined for hydrolysis of cinnamic picolinic anhydride and cinnamic 6-carboxypicolinic monoanhydride in 50% dioxane-H//2O at 30 degree C. At pH values less than 7, both water and hydronium ion catalyzed reactions are observed in hydrolysis of cinnamic picolinic anhydride. The latter reaction is also seen with cinnamic isonicotinic anhydride and is very likely associated with protonation of the pyridine nitrogen. Divalent metal ions (Cu**2** plus , Ni**2** plus , Co**2** plus , and Zn**2** plus ) exert a significant catalytic effect in the hydrolysis of cinnamic picolinic anhydride even though binding is weak (saturation effects were not observed). Rate enhancements ranging from 200-fold with 0. 0005 M Cu**2** plus to 10-fold with 0. 0005 M Zn**2** plus were obtained. The reactions at constant metal ion concentration are pH independent. Metal ion catalysis is not observed in the hydrolysis of cinnamic isonicotinic anhydride. Therefore, metal ion catalysis in the hydrolysis of cinnamic picolinic anhydride must be specifically associated with a chelation effect. The metal ion binding to cinnamic 6-carboxypicolinic monoanhydride is quite strong, and saturation occurs at low metal ion concentrations.