Permanganate Oxidations. III. Kinetics and Mechanisms of the Oxidation of Furfurals in Alkaline Media

Fillmore Freeman, Jay B. Brant, Norman B. Hester, Albert A. Kamego, Marc Kasner, Thomas G. McLaughlin, Edward W. Paull

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Abstract

A spectrophotometric stopped-flow kinetic study of the permanganate ion oxidation of furfural (I) and six 5-substituted furfurals at pH 11.5-13.3 reveals that the reaction follows two reaction paths. The minor pathway (Scheme I) is independent of hydroxyl ion concentration, and the major mechanism (Scheme II) is dependent on the first power of hydroxide ion concentration. Both reaction pathways are first order with respect to the concentration of I and permanganate ion. A correlation of the second-order rate constants with Hammett σ meta-substituent constants has been observed for the substituents 5-Me, 5-Et, 5-n-Bu, H, 5-01, and 5-Br at 25° with ρ = +1.30 (Scheme II). At pH 13.3 (Scheme II), ΔH≠ is 10.2 kcal/mol, ΔS≠ is -22.8 eu, and ks/ko is >1.8. Oxygen-18 experiments show that the solvent is the major source of oxygen introduced into I via Scheme II. The kinetic data are consistent with the formation of the hydrate anion of I followed by a hydride anion transfer to permanganate ion in the rate-determining step for the mechanism of Scheme II. It is postulated that the mechanism of Scheme I involves a direct attack of permanganate ion on I to give the permanganate ester, which decomposes in a subsequent slow step.

Original languageEnglish
Pages (from-to)982-985
Number of pages4
JournalJournal of Organic Chemistry
Volume35
Issue number4
DOIs
StatePublished - 1 Apr 1970

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Oxidation
Kinetics
Ions
Anions
Oxygen
Furaldehyde
Hydrates
Hydrides
Rate constants
Esters
permanganic acid
Experiments
hydroxide ion

Cite this

Freeman, F., Brant, J. B., Hester, N. B., Kamego, A. A., Kasner, M., McLaughlin, T. G., & Paull, E. W. (1970). Permanganate Oxidations. III. Kinetics and Mechanisms of the Oxidation of Furfurals in Alkaline Media. Journal of Organic Chemistry, 35(4), 982-985. https://doi.org/10.1021/jo00829a025
Freeman, Fillmore ; Brant, Jay B. ; Hester, Norman B. ; Kamego, Albert A. ; Kasner, Marc ; McLaughlin, Thomas G. ; Paull, Edward W. / Permanganate Oxidations. III. Kinetics and Mechanisms of the Oxidation of Furfurals in Alkaline Media. In: Journal of Organic Chemistry. 1970 ; Vol. 35, No. 4. pp. 982-985.
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abstract = "A spectrophotometric stopped-flow kinetic study of the permanganate ion oxidation of furfural (I) and six 5-substituted furfurals at pH 11.5-13.3 reveals that the reaction follows two reaction paths. The minor pathway (Scheme I) is independent of hydroxyl ion concentration, and the major mechanism (Scheme II) is dependent on the first power of hydroxide ion concentration. Both reaction pathways are first order with respect to the concentration of I and permanganate ion. A correlation of the second-order rate constants with Hammett σ meta-substituent constants has been observed for the substituents 5-Me, 5-Et, 5-n-Bu, H, 5-01, and 5-Br at 25° with ρ = +1.30 (Scheme II). At pH 13.3 (Scheme II), ΔH≠ is 10.2 kcal/mol, ΔS≠ is -22.8 eu, and ks/ko is >1.8. Oxygen-18 experiments show that the solvent is the major source of oxygen introduced into I via Scheme II. The kinetic data are consistent with the formation of the hydrate anion of I followed by a hydride anion transfer to permanganate ion in the rate-determining step for the mechanism of Scheme II. It is postulated that the mechanism of Scheme I involves a direct attack of permanganate ion on I to give the permanganate ester, which decomposes in a subsequent slow step.",
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Permanganate Oxidations. III. Kinetics and Mechanisms of the Oxidation of Furfurals in Alkaline Media. / Freeman, Fillmore; Brant, Jay B.; Hester, Norman B.; Kamego, Albert A.; Kasner, Marc; McLaughlin, Thomas G.; Paull, Edward W.

In: Journal of Organic Chemistry, Vol. 35, No. 4, 01.04.1970, p. 982-985.

Research output: Contribution to journalArticle

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T1 - Permanganate Oxidations. III. Kinetics and Mechanisms of the Oxidation of Furfurals in Alkaline Media

AU - Freeman, Fillmore

AU - Brant, Jay B.

AU - Hester, Norman B.

AU - Kamego, Albert A.

AU - Kasner, Marc

AU - McLaughlin, Thomas G.

AU - Paull, Edward W.

PY - 1970/4/1

Y1 - 1970/4/1

N2 - A spectrophotometric stopped-flow kinetic study of the permanganate ion oxidation of furfural (I) and six 5-substituted furfurals at pH 11.5-13.3 reveals that the reaction follows two reaction paths. The minor pathway (Scheme I) is independent of hydroxyl ion concentration, and the major mechanism (Scheme II) is dependent on the first power of hydroxide ion concentration. Both reaction pathways are first order with respect to the concentration of I and permanganate ion. A correlation of the second-order rate constants with Hammett σ meta-substituent constants has been observed for the substituents 5-Me, 5-Et, 5-n-Bu, H, 5-01, and 5-Br at 25° with ρ = +1.30 (Scheme II). At pH 13.3 (Scheme II), ΔH≠ is 10.2 kcal/mol, ΔS≠ is -22.8 eu, and ks/ko is >1.8. Oxygen-18 experiments show that the solvent is the major source of oxygen introduced into I via Scheme II. The kinetic data are consistent with the formation of the hydrate anion of I followed by a hydride anion transfer to permanganate ion in the rate-determining step for the mechanism of Scheme II. It is postulated that the mechanism of Scheme I involves a direct attack of permanganate ion on I to give the permanganate ester, which decomposes in a subsequent slow step.

AB - A spectrophotometric stopped-flow kinetic study of the permanganate ion oxidation of furfural (I) and six 5-substituted furfurals at pH 11.5-13.3 reveals that the reaction follows two reaction paths. The minor pathway (Scheme I) is independent of hydroxyl ion concentration, and the major mechanism (Scheme II) is dependent on the first power of hydroxide ion concentration. Both reaction pathways are first order with respect to the concentration of I and permanganate ion. A correlation of the second-order rate constants with Hammett σ meta-substituent constants has been observed for the substituents 5-Me, 5-Et, 5-n-Bu, H, 5-01, and 5-Br at 25° with ρ = +1.30 (Scheme II). At pH 13.3 (Scheme II), ΔH≠ is 10.2 kcal/mol, ΔS≠ is -22.8 eu, and ks/ko is >1.8. Oxygen-18 experiments show that the solvent is the major source of oxygen introduced into I via Scheme II. The kinetic data are consistent with the formation of the hydrate anion of I followed by a hydride anion transfer to permanganate ion in the rate-determining step for the mechanism of Scheme II. It is postulated that the mechanism of Scheme I involves a direct attack of permanganate ion on I to give the permanganate ester, which decomposes in a subsequent slow step.

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