Studies on New Derivatives of 8-Quinolinol as Chelating Agents. I. Syntheses, Coloration Reaction with Metal Ions and Acid Dissociation Constants of Some Azomethine and Aminomethyl Derivatives

Abstract

Azomethine derivatives of 8-hydroxyquinoline-2-carbaldehyde with aromatic and aliphatic amines and their aminomethyl derivatives were synthesized for the purpose of investigating their applications as analytical reagents. Spot tests with metal ions revealed that azomethine derivatives form intensely colored chelates, whereas aminomethyl derivatives form less intensely colored chelates. The acid dissociation constants were determined by means of potentiometric titration in 50 v/v% aqueous dioxane solution at 25±0.1°C. The values of pKNH+ and pKOH of 8-hydroxyquinoline-2-carbaldehyde, 2-(o-hydroxyphenylaminomethyl)-, 2-(p-chlorophenylaminomethyl)-, 2-(p-tolylaminomethyl)- and 2-(naphthylaminomethyl)-8-quinolinol are lower than those of 8-quinolinol. The phenyl substituent in 2 position of oxine moiety exerts an acid strengthening effect on these ligands. The basicity of the ligand N,N′-bis- (8-hydroxy-2-quinolylmethyl)ethylenediamine is higher than that of other oxine derivatives.