International Journal of Modern Science and Technology

ISSN 2456-0235

INDEXED IN 

International Journal of Modern Science and Technology, 1(3), 2016, Pages 106-110. 


Kinetics and mechanism of oxidation of 5-(4’-bromophenyl)-5-oxopentanoic acid by acid permanganate 

​S. Mahendran, C. Anbuselvan
​PG & Research Department of Chemistry, Presidency College, Chennai 600005, India.

​​Abstract
The manganese (II)-catalyzed oxidation of substituted δ-oxoacid by (δ-oxo acids) by acid permanganate, in aqueous acetic medium containing sulphuric acid, has been studied. The reaction is first order each in [oxoacid], [MnO4─] and [acid], less than unity order in both [substrate] and [catalyst], and also shows solvent isotope effect of 0.60 (k c’ H2O)/k c’ (DO)). At low [H+] the reaction is zero order with respect to [MnO4─]. 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 increase with decrease in temperature. The mechanism involving decomposition of the complex, formed by participation of the neighboring group of δ-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 from of oxo acid is proposed. A mechanism consistent with the observed kinetics results has been reported

​​Keywords: ​Kinetics, Reaction mechanisms, δ-oxoacid, Oxidation, Acid permanganate, Isokinetic relationships, Manganese.  . 


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