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Alkaline hexacyanoferrate(III) oxidation of substituted 4‐oxo acids: a mechanistic study
Author(s) -
Pushparaj F. J. Maria,
Kannan S.,
Vikram L.,
Kumar Lalitha S.,
Rangappa K. S.
Publication year - 2005
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.968
Subject(s) - chemistry , reaction rate constant , arrhenius equation , hydroxide , ionic strength , steric effects , reagent , aqueous solution , inorganic chemistry , kinetics , ion , arrhenius plot , equilibrium constant , activation energy , reaction rate , organic chemistry , catalysis , physics , quantum mechanics
The kinetics of the oxidation of substituted 4‐oxo‐4‐arylbutanoic acids by hexacyanoferrate(III) in aqueous alkaline medium were studied. The reactions are found to be first order in each of the reagents, the oxo acid, hydroxide ion and the hexacyanoferrate(III) ion. A mechanism involving the formation of enolate anion from the oxo compound and subsequent rate‐determining electron transfer is proposed. Application of the Olson–Simonson rule substantiated the participation of negatively charged ions in the rate‐determining step. The experimental rate constant is found to be composite, being the product of the equilibrium constant for the enolate anion formation and the rate constant of the oxidation step ( Kk 2 ). The effect of addition of solvents such as methanol and DMSO is discussed and a quantitative relationship is derived between the ionic strength and the composite rate constant. The low activation energies and even the negative activation energy in the oxidation of 4‐(3‐nitrophey1)‐4‐oxobutanoic acid are explained. The ρ values are positive and decrease with temperature. Contrary to the expected electronic effect, the methyl group in the ortho position accelerates the reaction owing to steric factors. From the intersection of the lines in the Hammett and Arrhenius plots, the isokinetic relationship is discussed. Copyright © 2005 John Wiley & Sons, Ltd.