Reactivity of Certain Piperidin-4-ols Towards Oxidation with Cerium(IV)

DOI: 10.1039/P29830001333

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 1333 - 1336 (1983)

Update date:2022-08-11

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Authors:

Devi, Chenniappan Vasantha

Selvaraj, Kuppusamy

Ramalingam, Kondareddiar

Ramarajan, Krishnasamy

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Article abstract of DOI:10.1039/P29830001333

Kinetics of the oxidation of six pairs of epimeric piperidin-4-ols by cerium(IV) in the presence of sulphuric acid in an aqueous acetic acid medium at 60 deg C have been investigated.The corresponding α-deuteriated piperidin-4-ols have been prepared and their oxidation rates measured.The oxidation is first-order in both oxidant and substrate at constant acid concentration.Mechanism involving free-redical intermediates are proposed.The observed kinetic isotope effect in the case of t-2,t-6-diphenyl-c-3-isopropyl-N-methylpiperidin-r-4-ol (4) (k_H/k_D= 6.26) suggests that the C-H (or C-D) bond of the carbinol carbon is involved in the rate-determining step.An alternative mechanism involving the participation of the O-H bond in the rate-limiting step is proposed to account for the absence of a kinetic isotope effect (k_H/k_D= 1.00) in the oxidation of t-2,t-6-diphenyl-c-3,c-5,N-trimethylpiperidin-r-4-ol (5) and c-2,c-6-diphenyl-t-3,t-5,N-trimethylpiperidin-r-4-ol (14).It is probable that both mechanisms operate simultaneously in the oxidation of those piperidin-4-ols which show a kinetic isotope effect of ca. 2.00.The conformational effects on the rates of oxidation are discussed.