Kinetics of reduction of [Co(NH₃)₅N₃]Cl₂ by iron (II) in CTAB/n-heptane/butanol/water reverse micelles

952-956The kinetic study of reduction of pentaammineazidocobalt(III) chloride complex by Mohr’s salt (ammonium ferrous sulphate) has been carried out in the water pools of cationic reverse micelles of cetyltrimethylammonium bromide (CTAB). The reaction is first order each in Co(III) complex and iron(II) in all water-to-surfactant molar ratios, i.e. at all W values. The observed pseudo first order rate constant (kobs) versus W plot shows highest rate at W = 8.33. The kinetics has been accounted for by a mechanism involving bimolecular azido-bridged inner-sphere intermediate complex formation between Co(III) complex and iron(II). The significant increase of rate in reverse micellar media as compared to that in aqueous medium is due to the lower micropolarity of the water pool and bound state of reactants in this reverse micellar media, both facilitating the intermediate formation. The activation parameters (standard enthalpy of activation, Δ‡Hº and standard entropy of activation, Δ‡Sº) of the reaction at different W values have been calculated which corroborate the kinetics of the reaction