Abstract
Schiff bases of 3-hydroxy-4-formylpyridine (1), pyridoxal (PL), pyridoxal-5'-phosphate (PLP), and related aldehydes with methyl valinate, n-butylamine, and various amino acids and their derivatives were prepared and their absorption spectra in various solvents and in acidic, neutral and alkaline methanol were measured. From the spectral analyses, the longest π bands of the eight possible molecular species of the Schiff base of 1 involved in acid-base equilibrium were determined as follows ; anion, 368 nm ; enolimine, 325 nm ; ketoenamine, 420 nm ; species with a phenolate and a pyridinium groups, 385 nm ; species with a protonated azomethine and a phenol group, 365 nm ; ketoenamine with a pyridinium group, 425 nm ; enolimine with a pyridinium group, 330 nm ; fully protonated species, 365 nm. Equilibria between equally protonated species were dependent on media and on the amine part. The wavelengths of the π bands were affected by media and slightly by the amine part. Corresponding species of Schiff bases of PL and PLP have the π band at the longer wavelength side of less than 10 nm. Infrared and proton magnetic resonance data of the Schiff bases are presented.
