Ionization constants of heterocyclic substances. Part X. Protonation of aminopyridine-2 (and-4)-thiones

Abstract

Protonation of 3- and 5-aminopyridine-2-thione and 3-aminopyridine-4-thione is shown to occur first at the primary amino-group, but 6-aminopyridine-2-thione (and probably 2-aminopyridine-4-thione) are protonated first at the sulphur atom. Ionisation constants and u.v. spectra of the mercapto-compounds and their S-methyl derivatives are reported and discussed.