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Indian Journal of Chemistry -Section A (IJC-A) >
IJC-A Vol.50A [2011] >
IJC-A Vol.50A(07) [July 2011] >
| 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 |
| Keywords: | Reaction mechanisms
Oxidation
Bromate oxidation
Arylbutanoic acids
Isokinetic relationships
Manganese |
| Issue Date: | Jul-2011 |
| Publisher: | NISCAIR-CSIR, India |
| 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. |
| Page(s): | 979-990 |
| CC License: |  CC Attribution-Noncommercial-No Derivative Works 2.5 India |
| ISSN: | 0975-0975(Online); 0376-4710(Print) |
| Source: | IJC-A Vol.50A(07) [July 2011]
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