A study of some metal ion catalysed reactions

Abstract

A study has been made of the reactivity of certain complexed and uncomplexed carboxylic acid derivatives of 8-quinolinol toward nucleophilic attack by hydroxide ion. Binding of 2-cyano-8- uinolinol to 1st row transition metal ions markedly increases the rate of base hydrolysis to the corresponding carboxamide. Similarly large rate enhancements (10® - 10®) have been observed for the metal ion promoted base hydrolysis of 2-carbomethoxy-8-quinolinol (M = Zn, Cu, Ni, Co and Mn). ase hydrolysis of the 1:1 complex of 8-acetoxy-2-carboxyquinoline with zinc(II) or copper(II) roceeds .7 x 1 0® times faster than base hydrolysis of the deprotonated ligand. Arrhenius parameters for the hydrolytic processes have been determined and possible mechanisms for the reactions are considered. The iodination of the metal ion complexes (M = Zn, Cu and Ni) of 2-acetyl-8-quinolinol has been investigated. The reactions exhibit substantial kinetic deuterium isotope effects (acetyl-d3) and are general base catalysed, indicating that the rate determining step involves ionization of the active H atom in the methyl group. Comparative studies, using 2-acetyl pyridine as a reference substrate, suggest that electrostatic facilitation of ionization may be of importance in the metal ion promoted reactions. A number of transition metal complexes of 2-carbethoxy pyridine have been prepared and characterised. Data for mono- and bis-ligand complexes are reported. Complex formation between copper(II) and the macrocyclic ligand 5,7,7,12,14,14-hexamethyl-l,4,8,11- etraazacyclotetradecane (tet a) has been studied using spectrophotometric and pH-stat techniques. Under the conditions of measurements the product is a blue complex Cu(tet a)(blue) . The rate law for the reaction in the presence of acetate ion has been established as: rate = k^[ Cu^+] [ tet a H+] + k^[ CuOAc+] [ tet a H+] + k^[ CuOAc+] f tet a Hj+1