Study of the Catalytic Constant of Phosphate Base in the Kinetics of Iodination of Pyrazole by Molecular Iodine in Aqueous Medium

Rachana D Bamb, Ranjana P Bhad

Abstract

The rapid kinetics of base catalysed iodination of pyrazole by molecular iodine has been studied in aqueous medium using phosphate buffer. The reaction is electrophilic substitution reaction and rate sows second order kinetics. The specific reaction rates have been determined at constant pH of 7 and temperature 23°C at various base concentrations of the buffer component in the range of 0.02 M to 0.1 M. The catalytic constant of the reaction is calculated from the slope of the graph of specific reaction rate versus base concentration which is found to be 675.4 M-2s-1. The reaction has been also studied kinetically at different pH and at constant base concentration of 0.1 M of the buffer component used. The rapidity of the reaction necessitates the use of special technique namely hydrodynamic voltammetry to study the progress of reaction. The decay of the unreacted iodine is followed by measuring the decrease in diffusion current at rotating platinum electrode. The linear proportionality of specific reaction rates with the concentration of base component provides the quantitative verification for the base catalysed reaction.