1953 年 73 巻 2 号 p. 140-145
Ionization constants and absorption spectra of 4-aminopyridine (A), its N-oxide (B), 4-aminoquinoline (C), and its N-oxide (D), were determined in water and in sulfuric acid as solvents. Results obtained are given below:
1) As shown in Table II, the N→O compounds were generally bathochromic compared to the N+-H type, in either solvent.
2) The pKa of the equilibrium such as (II) in aqueous solution was found to be 3.54 for (B) which is extremely small compared to that of 9.17 for (A) and (C).
3) The pKa of the equilibrium such as (VIII) in conc. sulfuric acid was: (A)=-6.55, (B)=-6.27, (C)=-7.11, (D)=-6.55, which showed that the values for the N-oxide compounds were larger in both cases.
The above results were explained from the resonance effect of the substituents, and the resonance energy contributed by the amino radical in (I) and (IV) were calculated as 22-23 kcal. per mole.