Reactivities of heterocyclic compounds in nitration. 6. Ionization constants of 2-anilinopyridines

The pKa values of 2-anilinopyridines with electron-acceptor substituents in the 3 and 5 positions of the pyridine ring and in the 2, 4, and 6 positions of the benzene ring determined by spectrophotometry range from 2.4 to -6.4. The sensitivity to the introduction of nitro groups in the pyridine ring is considerably higher than the sensitivity to introduction in the benzene ring in the case of both isomeric dinitro and tri- and tetranitro derivatives of 2-anilinopyridines.