The spectrophotometric method and the method of potentiometric titration were used to study the acid ionization of 11 bis-azo derivatives of chromotropic acid, both containing and not containing acid groups in the benzene rings.
Ionization of the first hydroxy group of the naphthalene ring is observed at pH 10. In the investigated cases, oxidation of the hydroxy groups of the benzene rings precedes the ionization of the hydroxy groups of the naphthalene ring.
It was shown by the Hückel MO LCAO method that in acid and neutral media the reagents are in a state of tautomeric equilibrium. During the dissociation of the first hydroxy group of the naphthalene ring, the equilibrium is entirely shifted in the direction of the azoid form.
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Savvin, S.B., Petrova, T.V. & Kuzin, E.L. Study of the acid ionization of certain reagents — bis-azo derivatives of chromotropic acid. Russ Chem Bull 18, 247–253 (1969). https://doi.org/10.1007/BF00905529
- Benzene Ring