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Title: Kinetics and mechanism of oxidation of some substituted 4-piperidones by pyridinium fluorochromate (PFC)
Authors: Dhar, R K
Varadarajan, R
Issue Date: Nov-1991
Publisher: NISCAIR-CSIR, India
Abstract: The kinetics of oxidation of several 3-alkyl and 3,5-dimethyl substituted 2,6-diphenylpiperidin-4- ones (1-6) by pyridinium fluorochromate (PFC) in the presence of perchloric acid in aqueous acetic acid medium have been investigated. Direct second order kinetics is observed, first order each in [oxidant] and [substrate]. A primary isotope effect, kC-H/kC-D = 4.2, suggests that the αC-H bond is cleaved in the rate determining step. An interesting order of reactivity has been found to be: 3-ethyl > 3-methyl > 3- isopropyl > 3-H > 3,5-dimethyl. An explanation has been presented to justify the above rate differences. Further, the effect of electron-withdrawing NO2 group or electron-donating OCH3 group present at the para position of the phenyl ring of these piperidones (7,8) on the rate of oxidation suggests participation of the phenyl group. 3-Hydroxy-substituted piperidin-4-ones and substituted pyrrolidine-3-carboxylic acids are the major products of oxidation. Activation energies and related thermodynamic parameters have been determined and compared. Aprobable mechanism consistent with experimental observations has been proposed.
Page(s): 936-940
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.30A(11) [November 1991]

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