Ferricyanide/ferrocyanide reaction

Formation of Red-Brown Product in Ferricyanide/Ferrocyanide Reaction... 

Principle The ferricyanide/ferrocyanide reaction is known as reaction Kamovsky-Roots (Karnovsky and Roots, 1964). A final product of this... 

Du J, Li Y, Lu J. Flow injection chemiluminescence determination of captopril based on its enhancing effect on the luminol-ferricyanide/ferrocyanide reaction. Luminescence 2002 17 169-172. 

In redox electrodes an inert metal conductor acts as a source or sink for electrons. The components of the half-reaction are the two oxidation states of a constituent of the electrolytic phase. Examples of this type of system include the ferric/ferrous electrode where the active components are cations, the ferricyanide/ferrocyanide electrode where they are anionic complexes, the hydrogen electrode, the chlorine electrode, etc. In the gaseous electrodes equilibrium exists between electrons in the metal, ions in solution and dissolved gas molecules. For the half-reaction... 

The Hill reaction can be monitored by measuring the oxygen produced with an oxygen electrode or a Warburg manometer, or by spectrophotometry. The ferricyanide - ferrocyanide reduction can readily be measured by the last method ferrocyanide acceptor and spectrophotometry are therefore used to measure the Hill reaction inhibiting effect of herbicides (Hill, 1937, 1940, 1965). 

Srikantan and Rao (79) reported that the ferrocyanide catalysis is not first order in peroxide as found by Kistiakowsky but much more complicated. No details of the experiments were given. They also studied the ferricyanide-peroxide reaction and found that in the dark there was a pronounced induction period after which the decomposition rate was first order in peroxide concentration. Illuminating for five minutes in bright sunlight removed this induction period but the subsequent first order rate is somewhat less than the original dark rate. They suggest that the induction period was the time taken to build up on... 

As an example, let s take the well-known reversible reaction of ferricyanide/ferrocyanide on an RRDE with Pt as ring and Pt as disk electrodes ... 

A way to reduce interferences by cooxi-dizable sample constituents is by keeping the applied electrode potential as low as possible. Therefore, a reaction partner is chosen to be electrochemically indicated that is converted at low potential. For this purpose, the natural electron acceptors of many oxidoreductases have been replaced by redox-active dyes or other reversible electron mediators. Among them are the ferricyanide/ferrocyanide couple, V-methylphenazinium sulfate, fer-rocenes, and benzoquinone. With these mediators an electrode potential around -1-200 mV can be applied, which decreases... 

A commonly used mediator is the ferricyanide/ferrocyanide couple, and Equations (10.9) and (10.10) show the reaction sequence involved ... 

For example, for a linear sweep of potential, we obtain curves as illustrated in Figure 1.13, which, upon differentiation, provides the corresponding cyclic voltammogram [130]. Of course, the same methodology can be used to study assisted-ion-transfer reactions such as the transfer of copper(II) assisted by 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline [131], acid-base reactions such the transfer of bromophenol blue [132], and to study electron transfer. Ding et al. have in this way confirmed that electron-transfer reactions between ferricyanide-ferrocyanide in water, and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-DCE, were heterogeneous [133,134]. 

The redox potentials were determined by a chemical titration of the reaction center in tris-LDAO buffer at pH 7.8 with a potassium ferricyanide/ferrocyanide redox couple. The state of oxidation of the special pair was monitored by optical absorption spectroscopy. At most 70% reversibility to the original reduced state of the special pair was achieved with potassium ferrocyanide. At that point the solutions were so dilute that the concentration of the special pair could not be measured with sufficient accuracy. 

A typical outer-sphere charge-transfer reaction is the ferricyanide-ferrocyanide redox couple... 

Hexa.cya.no Complexes. Ferrocyanide [13408-63 ] (hexakiscyanoferrate-(4—)), (Fe(CN) ) , is formed by reaction of iron(II) salts with excess aqueous cyanide. The reaction results in the release of 360 kJ/mol (86 kcal/mol) of heat. The thermodynamic stabiUty of the anion accounts for the success of the original method of synthesis, fusing nitrogenous animal residues (blood, horn, hides, etc) with iron and potassium carbonate. Chemical or electrolytic oxidation of the complex ion affords ferricyanide [13408-62-3] (hexakiscyanoferrate(3—)), [Fe(CN)g] , which has a formation constant that is larger by a factor of 10. However, hexakiscyanoferrate(3—) caimot be prepared by direct reaction of iron(III) and cyanide because significant amounts of iron(III) hydroxide also form. Hexacyanoferrate(4—) is quite inert and is nontoxic. In contrast, hexacyanoferrate(3—) is toxic because it is more labile and cyanide dissociates readily. Both complexes Hberate HCN upon addition of acids. 

For forced-convection studies, the cathodic reaction of copper deposition has been largely supplanted by the cathodic reduction of ferricyanide at a nickel or platinum surface. An alkaline-supported equimolar mixture of ferri- and ferrocyanide is normally used. If the anolyte and the catholyte in the electrochemical cell are not separated by a diaphragm, oxidation of ferrocyanide at the anode compensates for cathodic depletion of ferricyanide.3... 

Chemical complexes of various transition metals have been shown to promote N-nitrosation (28). These metal complexes include ferrocyanide, ferricyanide, cupric ion, molybate ion, cobalt species, and mercuric acetate. All of the reactions are thought to proceed by oxidation-reduction mechanisms. However, such promotion may not be characteristic of transition metal complexes in general, since ferricyanide ion has been shown to promote nitrosation in metalworking fluids, whereas ferric EDTA does not (2 0). Since the metalworking operation generates metal chips and fines which build up in the fluids, this reaction could be of significance in the promotion of nitrosamine formation in water-based metalworking fluids. 

The evidence for the formation of complex heteropoly-acids with tantalic acid is very comparable to that set forth in the case of niobic acid (see p. 165). Solutions of tantalates are readily hydrolysed in aqueous solution by boiling, and even more readily by the addition of mineral acids, acetic acid or succinic acid in the presence, however, of arsenious add, arsenic add, tartaric add or dtric add no precipitation of tantalic add takes place. Again, tincture of galls yields a yellow predpitate with solutions of tantalates which have been rendered feebly acid with sulphuric add this reaction does not, however, take place in the presence of ordinary tartaric add, racemic add or citric acid. Tartaric add also prevents the formation of the predpitates which are thrown down on the addition of potassium ferrocyanide or potassium ferricyanide to faintly acid solutions of tantalates, and hinders the precipitation of tantalic add from solutions in inorganic acids by the action of ammonia. In all these cases it is assumed that complex acids or their salts are produced, in consequence of which the usual reaction does not take place. 

A new development is that electrochemical oxidation of ferrocyanide to ferricyanide can be coupled with AD to give a very efficient electrocatalytic process [37]. Under these conditions, the amount of potassium ferricyanide needed for the reaction becomes catalytic and Eqs. 6D.6 and 7 can be added following Eq. 6D.4. Summation of Eq. 6D.1-6D.4, 6D.6, and 6D.7 gives 6D.8, showing that only water in addition to electricity is needed for the conversion of olefins to asymmetric diols and that hydrogen gas, released at the cathode, is the only byproduct of this process. In practice, sodium ferrocyanide is used in the reaction and the amount of this reagent used in comparison with the potassium ferricyanide method mentioned above has been reduced from 3.0 equiv. to 0.15 equiv. (relative to an equivalent of olefin). 

The accuracy of the ORP measurements depends on the temperature at which a measurement is taken. For solutions with reactions involving hydrogen and hydroxyl ions, the accuracy also depends on the pH of the water. In natural waters, many redox reactions occur simultaneously each reaction has its own temperature correction depending on the number of electrons transferred. Because of this complexity, some of the field meters are not designed to perform automatic temperature compensation. The temperature correction for such meters may be done with a so-called ZoBell s solution. It is a solution of 3 x 10 3 mole (M) potassium ferrocyanide and 2 x 10 2 M potassium ferricyanide in a 0.1 M potassium chloride solution. The Eh variations of the ZoBell s solution with temperature are tabulated for reference, and the sample Eh is corrected as follows ... 

The method employed is a modification of that proposed by Hoffman (H2). In this modification the disappearance of color is measured when yellow alkaline ferricyanide is reduced to nearly colorless ferrocyanide in the presence of glucose and heat. The reaction is catalyzed by the presence of cyanide ion, although this is not essential (M3). 

The standard equilibrium potential at the anode related to reaction (XXIV-7 is 7c° = 0.356 V. As oxygen is evolved owing to overvoltage from neutral solutions as late as the potential is about 1.2 V and from alkaline solution at about 0.8 V, the oxidation of ferrocyanide to ferricyanide can proceed with a 100 per... 

Relaxation Kinetics. The details of the experimental procedure have been described earlier (14). 0.1 M phosphate buffer, pH 7.0, containing 2 X 10"5 M EDTA was used in all relaxation experiments. These were performed with solutions of different initial reagent composition— either ferrocyanide was added to oxidized azurin or ferricyanide to reduced azurin. Temperature jumps of 2.9° or 4.7° were applied to the reaction solution. The subsequent transmission changes were monitored at 625 nm (absorption of oxidized azurin) or 420 nm (absorption of ferricyanide ). Each plotted value of the relaxation time or amplitude represents the average of at least four measurements. 

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