Equilibria and Absorption Spectra of Schiff Bases

Article abstract of DOI:10.1021/ja00539a017

Equilibria in the formation of Schiff bases between eight aromatic aldehydes including salicylaldehyde and pyridoxal 5'-phosphate with a variety of different amines, diamines, and amino acids have been investigated.The formation constants, the acid dissociation constants of the Schiff bases, and the absorption spectra of the various ionic species of the Schiff bases have been evaluated.The spectra have been resolved into components with log normal curves to provide a precise description of the band shapes and to permit estimation of tautomerisation constants.Constants for ring closure in the Schiff bases of diamines have also been estimated.In addition to the major tautomer, which has an ortho quinonoid structure, smaller amounts of both a phenolic tautomer and a tautomer with a dipolar ionic pyridine ring are present in small amounts.Results of this study are correlated with those of previous investigation on related systems and with spectra of two enzymes.