KINETICS AND MECHANISM OF PRUSSIAN BLUE FORMATION

Abstract

The kinetics of reaction between ferrocyanide and ferric ions under acidic conditions was studied at fixed ionic strength (0.1 M) and (25 ± 0.1) ^oC by using the stopped flow technique, under limiting conditions of [ferrocyanide] and with other reactants in excess. The reaction had first-order dependence on ferrocyanide, Fe(III) and H⁺ ion concentrations and had negative salt effect. On the basis of the experimental findings, a plausible mechanism for the formation of soluble form of Prussian blue (KFe{Fe(CN)₆}x H₂O) and rate law are proposed. The activation parameters for the title reaction are estimated. A relatively low energy of activation (23 kJ mol^-1) and high negative entropy of activation (-231 J K^-1 mol^-1) agree well with the proposed mechanism and configuration of complex ion leading to the formation of insoluble Prussian blue, Fe₄{Fe(CN)₆}₃ y H₂O.
KEY WORDS: Prussian blue, Kinetics, Ferrocyanide, Salt effect, Ferricferrocyanide

Bull. Chem. Soc. Ethiop. 2009, 23(1), 47-54.