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A mechanistic investigation of the oxidation of N,α-diphenylnitrones by dichloramine-T in aqueous acetonitrile medium - a non-linear Hammett plot

Manivarman S. (Department of Chemistry, Annamalai University, Tamil Nadu, India)
Rajarajan G. (Department of Chemistry, Annamalai University, Tamil Nadu, India)
Manikandan G. (Department of Chemistry, Annamalai University, Tamil Nadu, India)
Sekar M. (Department of Chemistry, Post Graduate Centre, Government Arts and Science College, Chidambaram, India)
Jayabharathi J. (Department of Chemistry, Annamalai University, Tamil Nadu, India)
Thanikachalam V. (Department of Chemistry, Annamalai University, Tamil Nadu, India)

The kinetics of oxidation of a number of meta- and para-substituted N,α-diphenylnitrones (nitrone) by dichloramine-T (DCT) was investigated in the presence of alkali in aqueous acetonitrile medium. The order with respect to DCT was one and to OH- an inverse fractional order. The reaction was first order with respect to nitrone. Both electron releasing and withdrawing substituents suppress the reaction rate. The observed rate constant for the substituents were plotted against the Hammett constant, σ, and a non-linear concave downward curve was obtained. The electron withdrawing substituents fall on one side of the curve, having a negative ρ value and the electron releasing substituents fall on the other side, with a positive ρ value. A mechanism is proposed and the derived rate law is in conformity with the observed results.

Keywords: nitrones, kinetics, dichloramine-T, non-linear concave downward curve