Collect. Czech. Chem. Commun. 1994, 59, 2057-2068

Study of Amino-Imino Tautomerism in Derivatives of 2-, 4- and 6-Aminonicotinic Acid

Svatava Smrčková, Kristina Juricová and Viktor Prutianov

Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6, Czech Republic


13C NMR spectra of p-nitrobenzoyl 2-, 4-, and 6-aminopyridine-3-carboxylates, their hydrochlorides, trifluoroacetates and 1-benzyl derivatives were studied. As found from the chemical shifts of pyridine carbon atoms C-2, C-4 and C-6, the free bases exist in the amino form whereas hydrochlorides and 1-substituted pyridinium derivatives in the imino form. Trifluoroacetates of the 2- and 6-amino derivatives have structure similar to that of amidiniumcarboxylates (parallel hydrogen bonds and partially ionic character) whereas trifluoroacetate of the 4-amino derivative is structurally close to the corresponding hydrochloride. The found structures were confirmed by 1H NMR and IR spectroscopy.