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) 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

Easy to use program “Simkine3” for simulating kinetic profiles of multi-step chemical Systems and optimisation of predictable rate coefficients therein

‘Simkine3’, a Delphi based software is developed to simulate the kinetic schemes of complex reaction mechanisms involving multiple sequential and competitive elementary steps for homogeneous and heterogeneous chemical reactions. Simkine3 is designed to translate the user specified mechanism into chemical first-order differential equations (ODEs) and optimise the estimated rate constants in such a way that simulated curves match the experimental kinetic profiles. TLSoda which uses backward differentiation method is utilised to solve resulting ODEs and Downhill Simplex method is used to optimise the estimated rate constants in a robotic way. An online help file is developed using HelpScrible Demo to guide the users of Simkine3. The versatility of the software is demonstrated by simulating the complex reaction between methylene violet and acidic bromate, a reaction which exhibits complex nonlinear kinetics. The new software is validated after testing it on a 19-step intricate mechanism involving 15 different species. The kinetic profiles of multiple simulated curves, illustrating the effect of initial concentrations of bromate, and bromide were matched with the corresponding experimental curves.DOI: http://dx.doi.org/10.4314/bcse.v26i2.1

<b>Kinetics and mechanism of Prussian blue formation</b>

The kinetics of reaction between ferrocyanide and ferric ions under acidic conditions was studied at fixed ionic strength (0.1 M) and (25 plus or minus 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

<b>Speciation and stability of methylene blue-metal-thiocyanate ion-association complexes</b>

With thiocyanate, zinc(II), cobalt(II) and copper(II) ions form stable anion, [M(SCN) 4]2-. This anion in turn with methylene blue (MB+) forms ion-pair of the type MB2[M(SCN)4] and turns methylene blue to violet. The stoichiometry and stability constants of the ion-association complexes were determined using Benesi-Hildebrand method and the stoichiometry was confirmed by Job’s continuous variation method. The kinetics of formation of ternary complexes was studied using stopped-flow technique. The equilibrium studies showed that the stability of ternary complexes increased in the order Co(II) > Cu(II) > Zn(II) and the formation rate constants increased in the order, Cu(II) > Zn(II) > Co(II). The relative stabilities indicate that cobalt is preferred to other two metals in the speciation of ternary complexes comparable with similar complexes in biosystems. This study also provides a method for the spectrophotometric determination of Co(II) and Zn(II) ions at nanogram levels at 25 oC and an ionic strength of 0.15 M

<b>Ruthenium(III) determination by kinetic-catalytic method using the Nile Blue-acidic chlorite reaction</b>

The mechanism of the Ru(III) catalysed oxidation of Nile blue (3-amino-7-diethylamino-8,9-benzo-2-phenoxazine chloride, NB+) by acidic chlorite were investigated by kinetic approach and using the stopped flow technique at 633 nm. The catalysed reaction had a first-order dependence on the concentrations of NB+, H+, ClO2- and catalyst. The pertinent mechanism, consistent with the experimental results is proposed. Based on the high sensitivity and selectivity of the reaction to the presence of Ru(III), using its catalytic efficiency on the oxidation of Nile blue (NB+) by acidic chlorite, a fixed-time kinetic method is reported for Ru(III) determination. Interference studies confirm

<b>kinetics and mechanism of reaction of acidic chlorite with phenoxazine dyes, Nile blue and Meldola’s blue</b>

The kinetics and mechanism of the oxidation of two phenoxazine dyes namely Nile blue (7-amino-3-diethylamino-8,9-benzo phenoxazine chloride, NB⁺) and Meldola’s blue (3- dimethylamino-8,9-benzo phenoxazine chloride, MB⁺) with acidic chlorite and hypochlorous acid have been investigated using a UV-visible and a stopped flow equipment. For both Nile blue and Meldola’s blue reactions the rates have first-order dependence on each substrate, chlorite and acid. Both reactions showed negative salt effect indicating the reaction is between the oppositely charged species, likely the substrate cation and chlorite anion. The acidic chlorite reaction with MB⁺ was very slow compared with NB⁺ and was studied at higher temperature of 40 ^oC. The overall third order rate constants for the reaction of acidic chlorite with Nile blue and Meldola’s blue were (0.363 plus or minus 0.005) M^-2 s^-1 at 25 ^oC and (3.09 plus or minus 0.08) x 10^-3 M^-2 s^-1 at 40 ^oC, respectively. The energy parameters for NB⁺ reaction were E_a = 47.8 kJ mol^-1, H^ = 40.4 kJ mol^-1 and S^ = -233 J K^-1 mol^-1, while the corresponding values for MB⁺ reaction were 62.4 kJ mol^-1, 54.6 kJ mol^-1 and -248 J K^-1 mol^-1, respectively. The second-order rate coefficients for HOCl reaction with Nile blue and Meldola’s blue at 25 ^oC were (5.14 plus or minus 0.01) x 10³ M^-1 s^-1 and (1.25 plus or minus 0.03) x 10² M^-1 s^-1, respectively

Removal of chromium and sulphide from tannery effluents

Bull. Chem. Soc. Ethiop., 3(1), 1-7 (1989)

Removal of chromium and sulphide from tannery effluents

Bull. Chem. Soc. Ethiop., 3(1), 1-7 (1989)

River pollution in developing countries - a case study effect of waste discharges on quality of ruiruaka river waters in Kenya

Bull. Chem. Soc. Ethiop., 4(2), 89-103 (1990)