KINETICS AND MECHANISM OF PRUSSIAN BLUE FORMATION

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) degrees C 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, Fe-4{Fe(CN)(6)}(3)y H2O.