Synthesis of some benzimadazole derivatives and kinetics studies of their oxidation using chloramine-t in alkaline medium

Manikyanahalli Narasigowda.Kumara and Muddegowda Harsha

The kinetics of oxidation of 2-phenyl-1Hbenzimidazole (BzlH), 2-(4-methoxyphenyl)-1H-benzimidazole (OMeBzlH), 2-(4-nitrophenyl)-1H-benzimidazole (NO2BzlH) by chloramine-T; (CAT) in presence of NaOH has been investigated at 297 K. Under similarexperimental conditions, the oxidation reactions follow identical kinetics for all the threebenzimidazoles with first order dependence each on [CAT]0 and [substrate] 0 and inverse fractional order dependence on [OH-]. Solvent composition shows negative effect indicating the involvement of negative ion-dipolar molecule in the rate determining step. Variation of ionic strength of the medium and addition of halide ions had no effect on the reaction rate. Addition of p-toluenesulphonamide (PTS), the reduction product had no effect on the rate of reaction.The reactions were studied at different temperatures and the composite activation parameters have been computed. Relative reactivity of oxidation of these follow the order: OMeBzlH >BzlH> NO2BzlH. This trend may be attributed to inductive effects. Finally a related rate law has been deduced.

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