Reduction of hexacyanoferrate

Ionic Strength Effect on the Rate of Reduction of Hexacyanoferrate(lII) by Ascorbic Acid 241... 

There have been fewer reports on the particle size dependence of catalysis by platinum-catalyzed redox reactions. A report by Sharma et al. [21] showed that platinum colloidal nanoparticles do not demonstrate the same dependence on particle size as gold nanoparticles do for the reduction of hexacyanoferrate (III) by thiosulfate [19]. Platinum nanoparticles protected by sodium di(2-ethylhexyl) sulfosuccinate (synthesized by a reverse micelle technique) exhibit an optimum size ( 38 nm) for the reduction of ferricyanide by thiosulfate (Fig. 18.2). The reason for an optimum particle size is not fully understood however, they proposed the following explanation a shift in the Fermi level occurs as the diameter is increased. 

The reduction of hexacyanoferrate(III) by tetrahydroborate and the alkaline hydrolysis of the latter compound have been studied. The former... 

Figure 4 shows UV-visible absorption spectra recorded in a spectropotentiostatic experiment in an OTTLE cell on reduction of hexacyanoferrate(III) at a sequence of applied potentials. Curve a is at +0.50 V vs SCE reference electrode, where the redox system is in the oxidized state ([Ee (CN)5] "/ [EeWi(CN)6]4- > 1000). Curve h is at +0.00 V vs SCE, where the redox system is in the reduced state... 

A detailed kinetic study of outer-sphere reduction of hexacyanoferrate(III) by enoliz-able/nonenolizable aldehydes in aqueous alkaline medium indicates that benzaldehyde (for which = 1-93) generally oxidizes more slowly than aliphatic aldehydes and that the corresponding Hammett and Taft reaction constants are 4-0.6488 and -9.8, respectively. ... 

FIG. 5 (a) Schematic diagram of the heterogeneous reduction of TCNQ by the hexacyanoferrate... 

FIG. 10 Potential dependence of the electron-transfer rate constant k i) normalized to the value at the potential of zero charge TCNQ reduction by hexacyanoferrate at the water-DCE... 

In contrast to a variety of oxidizable compounds, only a few examples for the detection of strong oxidants with transition metal hexacyanoferrates were shown. Among them, hydrogen peroxide is discussed in the following section. Except for H202, the reduction of carbon dioxide [91] and persulfate [92] by Prussian blue-modified electrode was shown. The detection of the latter is important in cosmetics. It should be noted that the reduction of Prussian blue to Prussian white occurs at the lowest redox potential as can be found in transition metal hexacyanoferrates. 

Kinetic and mechanistic studies of hexacyanoferrate(II) reductions include those of hypochlorite, of peroxodisulfate (for which activation volumes were determined), and of trart5-[Co(salen)(H20)2] (salen = A,A -ethylenebis(salicylideneaminate), (37)). Peroxonitrite oxidation of hexacyanoferrate(II) is first-order in peroxonitrite, zeroth-order in hexacyanoferra-te(II). The inference that the rate-limiting step in this reaction is decomposition of the oxidant is supported by activation volume data - the value of A for oxidation of hexacyanoferrate(II), -fllcm moU lies within the range established for peroxonitrite decomposition but is very different from the value of AF, -7cm moU ... 

Studies of medium effects on hexacyanoferrate(II) reductions have included those of dioxygen,iodate, peroxodisulfate, - [Co(NH3)5(DMSO)] +, and [Co(en)2Br2]+. Rate constants for reaction with dioxygen depended strongly on the electron-donor properties of the organic cosolvent. Rate constants for reduction of peroxodisulfate in several binary aqueous media were analyzed into their ion association and subsequent electron transfer components. Rate constants for reduction of [Co(en)2Br2] in methanol water and dioxan water mixtures were analyzed by a variety of correlatory equations (dielectric constant Grunwald-Winstein Swain Kamlet-Taft). 

To prepare metal hexacyanoferrate films, very frequently the following procedure was followed first a film of the respective metal, for example, cadmium [79], copper [80], silver [81], or nickel [82, 83] was elec-trochemically plated on the surface of a platinum electrode, and that was followed by chemical oxidation of the metal film in a solution of K3[Fe(CN)6], leading to the formation of the metal hexacyanoferrates. The same method has been used to produce films of nickel hexacyanoruthen-ate and hexacyanomanganate using the appropriate anions [83]. It is also possible to perform the oxidation of the deposited metals in solutions containing hexacyano-ferrate(II) by cyclic oxidation/reduction of the latter. In a similar way, films of copper heptacyanonitrosylferrate have been deposited [84]. 

There is no valid interpretation for the activation by OJ and by hexacyano-ferrate(III), although they fitted nicely in a reaction scheme with Cu(III) as the active species In the oxidation of an alcohol to an aldehyde Cu(III) would be reduced to Cu(I). In the subsequent reaction of Cu(I) with Oj, Cu(II)Oj was considered an intermediate yielding Cu(III) and H O. This intermediate would be in a reversible equilibrium with OJ and with the resting Cu(II)-enzyme. This resting enzyme would be oxidized by hexacyanoferrate(III) to the active Cu(III) species. There was unfortunately no indication in X-ray absorption measurements for the formation of Cu(III) with hexacyanoferrate(III) and the resting enzyme . EPR measurements indicated that Cu(II) was present in the active enzyme It was not possible, moreover, to detect Oj by the reduction of Fe(III)-cytochrome c in a galactose oxidase — galactose system... 

Figure 9 shows a cyclic voltammogram (CV) of hexacyanoferrate(III) (Fe(III)) in water observed at a gold microelectrode (8 fim wide x 33 fim long x 0.2 fim thick). A cathodic current at 200 mV corresponds to reduction of Fe(III) to Fe(II). At a micrometer-sized electrode, mass transfer of a solute in water to the electrode proceeds very efficiently owing to hemispherical diffusion of the solute. This is proved by a characteristic sigmoidal current-potential curve in the CV, different from a peak current observed at a millimeter-size electrode (linear diffusion) [32,64]. Using... 

Mediators such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) [166], hexacyanoferrate(III) [168] and CoPC [169], which have been applied to a carbon paste or ink, are reduced by the reaction with thiocholine and then reoxidised at the carbon electrode (Fig. 23.6). A second type of mediator has involved the addition of Prussian blue (ferric hex-anocyanoferrate) into an AChE and choline oxidase (ChO) bienzyme biosensor. Prussian blue mediates the reduction of hydrogen peroxide produced by the conversion of choline to betaine by ChO [170]. 

The driving force in the reduction of die Fe3+ is the considerably more favorable energetical situation of the hexacyanoferrate(II) as compared to hexacyanoferrate(III) see, in this regard, R.M. Izatt, G.D. Watt, C.H. Bartholomew, J.J. Christensen, Inorg. Chem. 9 (1970), pp. 

Figure 11.69 shows a cyclic voltammogram (CV) for the reversible Nernstian redox involving the reduction of potassium hexacyanoferrate(III) to potassium hexayanoferrite(II) ... 

Filter paper pulp (e.g. in the form of a Whatman filtration accelerator) cannot be used as the organic matter may cause appreciable reduction of the hexacyanoferrate(III). 

Blueprints are based on a photochemical reaction. The paper is treated with a solution of iron(III) ammonium citrate and potassium hexacyanoferrate(III) and dried in the dark. When a tracing-paper drawing is placed on the blueprint paper and exposed to light, Fe ions are reduced to Fe ions, which react with hexa-cyanoferrate(III) ions in the moist paper to form the blue color on the paper. The lines of the drawing block the light and prevent the reduction of Fe ions, resulting in white lines. Find out how sepia prints are made, and report on this information. 

The existence of homoerythrina alkaloids has been anticipated from biosynthetic considerations. Homoerythrina dienone 77 was synthesized in the following way. Oxidation of the diphenolic isoquinoline 86 with vanadium oxytrichloride in methylene chloride afforded the expected prohomoerythrinadienone 87 (47), which was transformed to the imine 88 in quantitative yield by 1 N sodium hydroxide at 0°C. Sodium borohydride reduction of the iminium chloride of 88 gave 76. Oxidative phenolic coupling of 76 with potassium hexacyanoferrate in methylene chloride afforded homoerythrina dienone 77 in 45% yield and homoery-sodienone 89a in 15% yield (48). Moreover, the lactam dienone 91 was prepared in excellent yield by oxidation of the N-acyltetrahydroquinoline 90 with potassium ferricyanide (49). 

V -(2-Aminophenyl)hydrazides are cyclized to 5 and oxidized to 1,2,4-benzotriazines 6 when treated with hydrochloric acid and sodium 3-nitrobenzenesulfonate.5,147 Similarly, A -(2-nitro-phenyl)hydrazides give 1,2-dihydro-l, 2,4-benzotriazines 5 when the nitro group is reduced with sodium amalgam in ethanol. In most cases, the initially formed dihydro compounds are not isolated, but are oxidized by potassium hexacyanoferrate(III) to the aromatic 1,2,4-benzotriazines 6.148 Reduction of the nitrohydrazones or the tautomeric azo compounds with zinc, catalytic hydrogenation,332 or elcctrochemically246 affords 1,2,4-benzotriazines 6.148 Electrochemical reduction of A"-(2-nitrophenyl)hydrazides yields 3-substituted 1,2,4-benzotriazines 6.140... 

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