Ionization constants of heterocyclic substances. Part IX. Protonation of aminopyridones and aminopyrimidones

Abstract

Ionization constants and u.v. spectra are reported and discussed for amino-2(and 4)-hydroxypyridines [amino-2-(and 4)-pyridones] and amino-2,4-dihydroxypyrimidines [aminopyrimidine-2,4-diones] and their O- and nuclear N-methyl derivatives.

Protonation of 3- and 5-amino-2-hydroxypyridine and 3,4-diamino-2-hydroxypyridine is shown to occur first at the 3(or 5)-amino group, but 4- and 6-amino-2-hydroxypyridine and 2- and 3-amino-4-hydroxypyridine are protonatied first at the oxygen atom. The most basic centre of 4,5-diamino-2,6-dihydroxypyrimidine is shown to be the 5-amino-group.