Oxidation of N,-diphenylnitrones by N-chlorosuccinimide in alkaline medium – A non-linear Hammett plot

The kinetics of oxidation of some substituted N,a-diphenylnitrones by N-chlorosuccinimide (NCS) to yield benzaldehyde and nitrosobenzene was studied. The reaction follows first order kinetics with respect to (NCS) and fractional order with respect to (nitrone). The order with respect to alkali was inverse fractional order. The reaction exhibited both negative and positive Hammett reaction constants depending upon the nature of substituents. A plot of rate constant (log k) and s gave a concave downward curve. The electron releasing substituents fall on one side of curve and electron withdrawing substituents fall on another side. The activation parameters were calculated. A probable mechanism consistent with experimental observations has been proposed.