P. J. Kovi, Connie Miller, S. Schulman
Nov 1, 1972
Citations
0
Influential Citations
5
Citations
Journal
Analytica Chimica Acta
Abstract
Abstract pH and Hammett acidity dependences of the electronic absorption and fluorescence spectra of quinaldic acid. quinoline-8-carboxylic acid and their methyl esters have been studied. Conversions of the quinoline-like absorption spectra of the anions to quinolinium-like absorption spectra of the uncharged species show that the uncharged ground state species derived from the free acids consist overwhelmingly of the zwitterions. The excited singly charged cation of quinaldic acid appears to undergo an acidity-dependent phototautomerism. However, the 8-isomer does not exhibit this phenomenon. The long emission wavelengths of the esters relative to the zwitterions indicate that of the two electron-withdrawing groups, the carboxyl group is stronger than the heterocyclic nitrogen in the excited state. The fluorescence of quinoline-8-carboxylic acid in sulfuric acid could be very useful for quantitative analysis of transition metal chelates of this ligand.