Spectroscopic study of phenyl- and 4-pyridylmalondialdehydes

Abstract

4-Pyridylmalondialdehyde ( 1) and phenylmalondialdehyde ( 2) and their potassium salts were investigated by 1H and 13C NMR, Raman and UV spectroscopy. Three forms of 1 and two forms of 2 were found in water or DMSO solution depending on the pH by means of UV, 1H and 13C NMR spectroscopy. For 2 the chemical exchange between two cis-enol tautomers was observed, while the structure of 1 in the solution is zwitterionic. From the UV measurements and potentiometric titrations p K 1=1.9±0.1, p K 2=7.2±0,1 for 1 and p K=4.0±0.2 for 2 were evaluated. For 1 the Raman spectra of solid state and DMSO solution are very similar, while for 2 they differ significantly. Butylamine was used as a model compound for the study of the potential interaction of malondialdehyde with compounds containing amino groups. The effect of addition of butylamine on the spectra of both malondialdehyde derivatives were indistinguishable from that corresponding to protonation–deprotonation processes.