Spectrophotometric determination of the second dissociation constants of the aminoquinolines

The second dissociation constants representing the transition from monocation to dication for all of the isomeric aminoquinolines have been determined as pKa' values. The analogous values for 2- and 4-aminopyridine have been recalculated using a revised H_O scale. The accurate determination of the second pKa values follows from measurement, for the first time, of the ultraviolet spectra of all the mono- and dications of the aminoquinolines.