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Quantitative Assessment of Relative Reactivity of Molecular Halogens in the Kinetics of Halogenations of 2-Methylthiazole in Aqueous Medium using Hydrodynamic Voltammetry

Sandhya B. Walke, Shantaram L. Bonde and Ranjana P. Bhadane

The relative reactivity of different halogenating reagents in the electrophilic substitution reactions has been quantitatively investigated using kinetics as an investigational tool. In the present study, the halogenation of 2-methylthiazo le in aqueous medium has been studied at 23.5 0 C using I 2 , Cl 2 and Br 2 as the halogenating reagents. The presence of electron donating methyl group activates the thiazole ring towards the elctrophilic substitution reaction. The reactions follow the second order kinetics. The rapidity of the reactions necessitated the use of a special technique i.e. hydrodynamic voltammetry, to follow the course of the reaction. The extent of reactions was measured by following the decrease of nano diffusion current due to the reduction of halogenating reagents with time using rotating micro platinum cathode. The order of specific reaction rates was observed as k Bromination > k Clorination > k Iodination . The kinetic study has also been carried out at different temperatures to determine the various activation parameters. The kinetic data thus invoked justifies the quantitativ e assessment of the comparative reactivity of these halogenating reagents towards the halogenation of 2-methylthiazole.