Chemistry of Heterocyclic Compounds

, Volume 27, Issue 10, pp 1064–1069 | Cite as

Effect of the pH of the medium on the electronic absorption spectra and structure of 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone

  • B. E. Zaitsev
  • E. V. Nikiforov
  • M. A. Ryabov
  • G. V. Sheban


On the basis of the electronic absorption spectra it was found that 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone exists in acidic solutions in mono- and diprotonated forms. It was established by means of calculations by the Pariser—Parr—Pople (PPP) method that in the neutral and protonated forms the quinone hydrazone tautomer of the phenylazopyrazolone is more stable than the azo tautomer, and it was determined that the protonation center is the N(2) atom of the pyrazolone ring. The diprotonated form is most likely the quinone hydrazone tautomer protonated at the heteroring N(2) atom and the α-nitrogen atom of the azo group. In an alkaline medium the phenylazopyrazolone exists in the form of an anion with predominance of the azo form. The effect of substituents ion the diazo component of the phenylazopyrazolone on the long-wave bands of the electronic absorption spectra in various media was explained on the basis of calculation of the distribution of the π-electron density during electron transitions.


Organic Chemistry Acidic Solution Quinone Electronic Absorption Electron Transition 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Literature Cited

  1. 1.
    B. I. Stepanov, Introduction to the Chemistry and Technology of Organic Dyes [in Russian], Khimiya, Moscow (1984).Google Scholar
  2. 2.
    J. Elguero, C. Marzin, A. R. Katritzky, and P. Linda, The Tautomerism of Heterocycles, Academic Press, New York-London (1976), p. 336.Google Scholar
  3. 3.
    K. A. Hafez, E. M. Kayed, and K. U. Sadek, J. Heterocycl. Chem., 22, 241 (1985).Google Scholar
  4. 4.
    J. Elguero, R. Jacquier, and G. Tarrago, Bull. Soc. Chim. France, No. 9, 2990 (1966).Google Scholar
  5. 5.
    J. Arriau, J. P. Campillo, J. Elguero, and J. M. Pereillo, Tetrahedron, 30, 1345 (1974).Google Scholar
  6. 6.
    B. E. Zaitsev, V. A. Zaitseva, A. K. Molodkin, and E. S. Obraztsova, Zh. Neorg. Khim., 24, 127 (1979).Google Scholar
  7. 7.
    A. Lycka and D. Snobl, Coll. Czech. Chem. Commun., 42, 892 (1981).Google Scholar
  8. 8.
    L. G. Kuz'mina, L. P. Grigor'eva, Yu. T. Struchkov, Z. I. Ezhkova, B. E. Zaitsev, V. A. Zaitseva, and P. P. Pron'kin, Khim. Geterotsikl. Soedin., No. 6, 816 (1985).Google Scholar
  9. 9.
    I. S. Ioffe, L. M. Kryukova, and L. Yu. Kim, Zh. Org. Khim., 7, 2193 (1971).Google Scholar
  10. 10.
    D. Simov, S. Stoyanov, and S. Tomov, Godishnik Sofiisk. Univ. “Kliment Okhridski”: Khim. Fak., 74, 155 (1979/1980).Google Scholar
  11. 11.
    P. Nikolov, P. Fratev, S. Stoyanov, and O. E. Polanskii (Polansky), Z. Naturforsch., 36A, 191 (1981).Google Scholar
  12. 12.
    J. J. Trotter, Appl. Spectr., 31, 30 (1977).Google Scholar
  13. 13.
    A. Albert and E. Sergeant, Ionization Constants of Acids and Bases [Russian translation], Khimiya, Moscow-Leningrad (1964).Google Scholar
  14. 14.
    M. Dewar, Molecular Orbital Theory in Organic Chemistry [Russian translation], Mir, Moscow (1972), p. 464.Google Scholar

Copyright information

© Plenum Publishing Corporation 1992

Authors and Affiliations

  • B. E. Zaitsev
    • 1
  • E. V. Nikiforov
    • 1
  • M. A. Ryabov
    • 1
  • G. V. Sheban
    • 1
  1. 1.Patrice Lumumba International-Friendship UniversityMoscow

Personalised recommendations