The kinetics and mechanism of oxidation of hexacyanoferrate(II) by periodate ion in highly alkaline aqueous medium

The oxidation of hexacyanoferrate(II) by periodate ion has been studied spectrophotometrically by registering an increase in absorbance at 420 nm (λ_max of yellow colored Fe(CN)₆ ^3?] complex under pseudo first-order conditions by taking excess of IO₄ ^?] over Fe(CN)₆ ^4?]. The reaction conditions were: pH = 9.5 ± 0.02, I = 0.1 M (NaCl) and Temp. = 25 ± 0.1 °C. The reaction exhibited first-order dependence on each IO₄ ^?] and Fe(CN)₆ ^4?]. The effects of variations of pH, ionic strength and temperature were also studied. The experimental observations revealed that the periodate ion exists in its protonated forms viz. H₂IO₆]^3? and H₃IO₆]^2? while Fe(CN)₆]^4? is present in its deprotonated form throughout the pH region selected for the present study. It has also been observed that deprotonated form of Fe(CN)₆ ^4?] and protonated forms of periodate ion are the most reactive species towards oxidation of Fe(CN)₆ ^4?]. The repetitive spectral scan is provided as an evidence to prove the conversion of Fe(CN)₆ ^4?] to Fe(CN)₆ ^3?] in the present reaction. The activation parameters have also been computed using the Eyring’s plot and found to be, ΔH? = 51.53 ± 0.06 kJ mol^?1, ΔS? = ?97.12 ± 1.57 J K^?1 mol^?1 and provided in support of a most plausible mechanistic scheme for the reaction under study.