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

The kinetics of oxidation of a number of metaand 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 OHan 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.