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|Title:||Mechanistic investigations on manganese(II) catalyzed oxidation of substituted 4-oxo-4-arylbutanoic acids by bromate in acid medium|
|Authors:||Reddy, Cherkupally Sanjeeva|
Manjari, Padma Sunitha
|Abstract:||The manganese(II)-catalyzed oxidation of substituted 4-oxo-4-arylbutanoic acids (4-oxo acids) by bromate, in aqueous acetic acid medium containing sulphuric acid, has been studied. The reaction is first order each in [bromate] and [acid], less than unity order in both [substrate] and [catalyst], and also shows solvent isotope effect of 0.60 (kc′ (H2O)/kc′ (D2O)). Oxidation rate is not much affected by electron withdrawing substituents, although it is susceptible to electron demand at the seat of the reaction. The linear free-energy relationship is characterized by smooth curves in Hammett plots of log k versus σ. However, the plots are linear with excellent correlation coefficient at all the studied temperatures when Brown’s σ+ values are used. The reaction constant is negative and increases with decrease in temperature. The mechanism involving decomposition of the complex, formed by participation of the neighboring group of 4-oxo acid and intramolecular catalysis of Mn(II) is proposed, wherein, both the C–C bond-breaking and C–O bond-making in the oxidation are involved. However, these two processes are influenced in different ways by the electron withdrawing and electron releasing substituents. A π-complex formation between Mn(II) and -ene of the enol form of oxo acid is proposed.|
|Appears in Collections:||IJC-A Vol.50A(07) [July 2011]|
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