Chemistry of Heterocyclic Compounds, Vol. 40, No. 11, 2004
SELF-OSCILLATING REACTION
IN THE FURAN SERIES
T. I. Gubina1, A. N. Pankratov2, V. I. Labunskaya1, and S. M. Rogacheva3
It was found for the first time that the acid hydrolysis of 2,5-dimethylfuran in water–ethanol solutions
has self-oscillating character. Oscillations in the concentrations of the two products 2,5-hexanedione
and an unidentified compound X were detected by GLC. The ranges of hydrochloric acid and ethanol
concentrations in which these oscillations appear were determined. It is suggested that the formation of
compound X results from tautomeric transformations of 2,5-hexanedione under the reaction conditions.
Quantum-chemical calculations showed that the possible tautomers are formed with equal probability.
Keywords: 2,5-dimethylfuran, tautomers, self-oscillating reaction, acid hydrolysis.
During the development of a method for the production of thiophenes and selenophenes by the
recyclization of furans in water–ethanol media under the conditions of acid catalysis it was shown that the
reaction takes place in two directions, one of which includes a stage involving the formation of a diketone, i.e.,
hydrolysis. Kinetic investigations of the hydrolysis of 2,5-dimethylfuran (1) in 50% ethanol under the influence
of HCl revealed the formation of 2,5-hexanedione (2) and an unidentified compound X. During the reaction the
ratio of the concentrations of the products varied with some degree of periodicity, i.e., as it accumulated one
product changed into the other, and these transformations were self-oscillating in nature [1, 2].
Study of the behavior of furan compounds in aqueous and water–alcohol media under the conditions of
acid catalysis is of great theoretical and practical interest in so far as oscillating chemical reactions take place in
various types of processes that determine the vital activity of living organisms [3], while furan derivatives are
physiologically active substances.
In the present work in order to determine the boundary conditions for the appearance of the above-
mentioned transformations the kinetics of the hydrolysis of dimethylfuran 1 in 50% aqueous ethanol with
various hydrochloric acid concentrations (1.5, 2.0, 3.0, 3.5 N) were investigated by GLC. The results of the
experiments are presented in Fig. 1. As seen, the fluctuations in the contents of the dione 2 and compound X in
the reaction medium are observed at HCl concentrations (c) of 1.5-2.0 M. At c = 3 M both products are formed,
but the ratio of their amounts in the reaction medium does not change with time.
The experiments in 60 and 80% ethanol at HCl concentrations of 2.0 and 2.5 N (the dimethylfuran is
poorly soluble in the 40% alcohol) showed that in 80% alcohol at the indicated acid concentrations only the
hexanedione 2 is formed, while in 60% ethanol the concentrations of compound 2 and X oscillate in both cases
(Fig. 2).
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1
2
Saratov State Technical University, Saratov, Russia; e-mail: aus@sstu.saratov.su. Saratov State
3
University, Saratov, Russia. Saratov Military Institute of Radiation, Chemical, and Biological Protection,
Saratov, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1619-1625, November,
2004. Original article submitted January 3, 2002; revision submitted October 25, 2002.
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0009-3122/04/4011-1396©2004 Springer Science+Business Media, Inc.