Self-association of pyridine monocarboxylic acids and their esters in aqueous solution. A study by ultraviolet spectroscopy

Abstract

The ultraviolet spectra of pyridine monocarboxylic acids and their methyl or ethyl esters in aqueous solution, at different pH values, show an hypochromic effect over the range 10 −6–10 −1 M, which is interpreted in terms of dimerization and polymerization. In general, the values calculated for the association constants show that the studied interaction is a function of the nature and position of the substituent groups in the pyridine ring, and of the cationic, zwitterionic, anionic or neutral species which predominate at each of the selected pH values.