Protonation equilibria and complex formation ability of 2-amino-3-aminomethyl-4,6-disubstituted pyridines

Abstract

The protonation equilibria of 2-amino-3-aminomethyl-4,6-disubstituted pyridines were studied by potentiometric titrations and by UV and 13C NMR spectrometry. Protonation constants log K 1 and log K 2 potentiometrically determined for 4-methoxymethyl-6-methyl (8.959 and 5.778), 6-methoxymethyl-4-methyl (8.964 and 5.407), and 4,6-dimethyl derivative (9.141 and 6.604), were compared with the values obtained by the spectrometric methods. Complex formation of these compounds with Cu(II), Ni(II), Zn(II) and Co(II) was investigated in solution whereby the outstanding effect of the pH value was established and the presence of the species with 1 : 1 and 2 : 1 ligand to metal ratios confirmed. Stability constants obtained by potentiometric titrations show a decrease of the complex stability in the order Cu > Ni > Zn with respective log β 1 values of 5.85, 3.56 and 2.93. Series of complexes isolated in the crude state were characterized by elemental analyses and spectrometric data, the latter serving also as the basis for making an attempt at the discernment of the coordination mode and sites.