Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
39, Number 10, October 2001, pp. 431-440
Tautomer Interconversion of 2,4-Pentanedione During Gas Chromatography
on an Oxidized Cyano-Modified Capillary Column
P.J. Skrdla*, V. Antonucci, and C. Lindemann
Merck & Co., Inc., P.O. Box 2000, Rahway, NJ 07065-0900
The tautomerization of 2,4-pentanedione (acetylacetone) is examined
on a microbore column containing an acid-modified stationary phase made by oxidizing
a commercially available cyano-modified column. This stationary phase is found
to provide separation of the two tautomers, which allows the kinetic and thermodynamic
properties of the on-column interconversion to be investigated. The enol-to-keto
tautomerization is found to occur primarily in the stationary phase, being enthalpically
driven. By treating the column as a reactor, the interconversion is investigated
as a function of temperature. Monitoring the loss of the more gas-stable ‘enol’
tautomer makes it possible to extract an energy of activation for the net tautomerization
(42.7 kJ/mol), because the reaction is found to obey pseudo first-order kinetics.
Simple peak-shape analysis of the major component (enol), which is used commonly
in treatments of peak tailing, provides insight into the nature of the retention
processes of the two tautomers as well as information on chromatographic optimization.
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