Kinetics and mechanism of hydantoic ring opening. The alkaline hydrolysis of 3-arylimidazolidine-2,4-diones to 5-arylhydantoic acids
- 1 January 1978
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 5,p. 493-497
- https://doi.org/10.1039/p29780000493
Abstract
The kinetics of hydrolysis of 3-arylimidazolidine-2,4-diones to 5-arylhydantoic acids were studied in aqueous solution over the pH range 8–14 at 25°. In strongly alkaline media (pH > 11.5), an ionisation equilibrium gives rise to an unreactive anion. The pKa values determined both spectrophotometrically and kinetically for the unsubstituted derivative are in good agreement. In mildly alkaline media (pH < 11.5), the observed rates have a first-order dependence on hydroxide ion concentration and no general catalysis is detected. The value of the Hammett parameter (ρ 0.8), the low deuterium isotope solvent effect (kH2O /kD2O ca. 0.7), and the markedly negative values of the entropies of activation (–30 cal mol–1 K–1 < ΔS‡ < –20 cal mol–1 K–1) are rationalized in terms of a rate-determining hydroxide ion attack which is in agreement with the pKa value of the leaving group of 3-arylhydantoins.Keywords
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