The 2-oxocyclohexanecarboxylic acid keto-enol system in aqueous solution
J A Chang1, A J Kresge, V A Nikolaev
1Contribution from the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
Journal of the American Chemical Society
|June 6, 2003
Summary
Flash photolysis generated 2-oxocyclohexylideneketene, which hydrated to an enol and isomerized to the keto form of 2-oxocyclohexanecarboxylic acid. This study determined the keto-enol equilibrium constant for this acid.
Area of Science:
- Organic Chemistry
- Photochemistry
- Physical Chemistry
Background:
- Keto-enol tautomerism is a fundamental concept in organic chemistry.
- Understanding the equilibrium and kinetics of these forms is crucial for reaction mechanisms.
- Previous assumptions about the stability of enol forms may require reevaluation.
Purpose of the Study:
- To investigate the photochemistry of specific diazodiones and dioxinones in aqueous solution.
- To characterize the keto-enol tautomerism of 2-oxocyclohexanecarboxylic acid.
- To determine the keto-enol equilibrium constant and compare it with related systems.
Main Methods:
- Flash photolysis of diazodiones and dioxinones in aqueous solution.
- Kinetic measurements of ketonization in various acidic, basic, and buffer solutions.
- Measurement of enolization rates using bromine as an enol scavenger.
- Determination of the keto-enol equilibrium constant (pK(E)).
Main Results:
- Flash photolysis produced 2-oxocyclohexylideneketene, which hydrated to the enol of 2-oxocyclohexanecarboxylic acid.
- The enol isomerized to the keto form, a process also observed for solid enol.
- Ketonization and enolization rates were measured, yielding a pK(E) of 1.27 for 2-oxocyclohexanecarboxylic acid.
- Significant differences were observed compared to the 2-oxocyclopentanecarboxylic acid system.
Conclusions:
- The study elucidates the photochemical generation and subsequent keto-enol tautomerism of 2-oxocyclohexanecarboxylic acid.
- The determined equilibrium constant and kinetic data provide new insights into this system.
- The findings challenge previous beliefs about the stability of the enol form and highlight differences with a related cyclic system.
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