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Osmium (VIII) catalyzed kinetics and mechanism of indoles oxidation with Aryl‐N‐haloamines in alkaline medium
Author(s) -
Rangappa K. S.,
Ramachandra H.,
Mahadevappa D. S.,
Gowda N. M. Made
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:4<265::aid-kin4>3.0.co;2-t
Subject(s) - chemistry , substituent , catalysis , arrhenius equation , enthalpy , medicinal chemistry , ionic strength , kinetics , reaction rate , inorganic chemistry , activation energy , aqueous solution , organic chemistry , thermodynamics , physics , quantum mechanics
The kinetics of oxidation of the title substrates by sodium N ‐haloarylsulfonamides (or ary‐ N ‐haloamines), chloramine‐T (CAT), bromamine‐T (BAT), chloramine‐B (CAB), and bromamine‐B (BAB), catalyzed by osmium(VIII) in alkaline medium has been studied at 30°C. The corresponding oxindoles and arylsulfonamides have been characterized as reaction products. The reaction rate shows a first‐order dependence each on |indole| 0 and |oxidant| 0 , a fractional‐order on |Os(VIII)|, and an inverse first‐order on |OH − |. Addition of arylsulfon‐amide, chloride and 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 and Eyring plots. Hammett correlation of substituent effects indicates an LFE relationship with ρ = −1.0, showing the formation of an electron deficient transition state. From enthalpy‐entropy relationships and Exner correlations, the isokinetic temperatures (333 K and 326 K) have been determined for the reactions of CAT and BAT, respectively. Proton inventory studies in H 2 O‐D 2 O 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. © 1996 John Wiley & Sons, Inc.