Mechanistic investigations of the oxidation of indoles with bromamine-T in alkaline medium catalyzed by Os(VIII)

Ramachandra, H. and Rangappa, K.S. and Mahadevappa, D.S. and Jagadeesha, M.B. (1999) Mechanistic investigations of the oxidation of indoles with bromamine-T in alkaline medium catalyzed by Os(VIII). Oxidation communications, 22 (2). pp. 248-258.

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Abstract

The kinetics of oxidation of 5 substituted indoles (Y-In, where Y = H, Cl, Br, NO2, CH3 and OCH3) by sodium-N-bromo-p-toluenesulphonamide or bromamine-T (BAT) in the presence of NaOH and catalyzed by Os(VIII) in 10 % vol. methanol medium has been studied at 303 K. The corresponding oxindoles and p-toluenesulphonamide (PTS) have been characterized as reaction products. The reaction rate shows a first order dependence each on indole](0) and BAT](0), a fraction order on Os(VIII)] and an inverse first order on OH-]. Addition of p-toluenesulphanamide, chloride, bromide and variation of ionic strength of the medium have no effect on the reaction rate. There is a negative effect of dielectric constant of the solvent. Activation parameters have been calculated from the Arrhenius plots. The Hammett correlation of substituent effects indicates a linear free energy relationship with rho+ = - 1.0 showing the formation of an electron deficient transition state. From enthalpy-entropy relationships and the Exner correlations, the isokinetic temperature beta was found to be 330 K, indicating enthalpy as a controlling factor. Proton inventory studies in H2O-D2O mixtures have shown the involvement of a single exchangeable proton of OH- ion in the transition state. A mechanism consistent with the observed kinetics has been proposed.

Item Type: Article
Subjects: C Chemical Science > Chemistry
Divisions: Department of > Chemistry
Depositing User: lpa venkatesh user
Date Deposited: 14 Jun 2021 07:45
Last Modified: 14 Jun 2021 07:45
URI: http://eprints.uni-mysore.ac.in/id/eprint/16846

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