Hexacyanoferrate III ions

12 HEXACYANOFERRATE(III) IONS [Fe(CN)6] 3 Solubility Alkali and alkaline earth hexacyanoferrate(III)s are soluble in water, so is iron(III) hexacyanoferrate(III). Those of most other metals are insoluble or sparingly soluble. Metal hexacyanoferrate(III)s are in general more soluble than metal hexacyanoferrate(II)s. 

To study these reactions use a 0 033m solution of potassium hexacyano-ferrate(III) K3[Fe(CN)6]. 

Concentrated sulphuric acid On warming a solid hexacyanoferrate(III) with this acid, it is decomposed completely, carbon monoxide gas being evolved  

With dilute sulphuric acid, no reaction occurs in the cold, but on boiling hydrocyanic acid (POISON) is evolved  

This test must be carried out in a fume cupboard with good ventilation. 

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However, 4-aminophenazone when treated with a mild oxidising agent such as hexacyanoferrate(III) ions in alkaline solution and in the presence of a phenol, reacts to form a dye which can be extracted with chloroform. The absorbance of this solution can be used to ascertain the amount of phenol present and this provides a good method for the determination of traces of phenols. 

Nickel hexacyanoferrate (NiHCF) films can be prepared by electrochemical oxidation of nickel electrodes in the presence of hexacyanoferrate(III) ions,141 or by voltammetric cycling of inert substrate electrodes in solutions containing nickel(II) and hexacyanoferrate(III) ions.142 NiHCF films do not possess low-energy intervalent CT bands, however, when deposited on ITO they are observed to reversibly switch from yellow to colorless on electroreduction.143... 

Iron(III) very readily forms complexes, which are commonly 6-coordinate and octahedral. The pale violet hexaaquo-ion [Fe(H20)6]3+ is only found as such in a few solid hydrated salts (or in their acidified solutions), for example Fe2(S04)3.9H20. Fe(C104)3.10H20. In many other salts, the anion may form a complex with the iron(III) and produce a consequent colour change, for example iron(III) chloride hydrate or solution, p. 394. Stable anionic complexes are formed with a number of ions, for example with ethanedioate (oxalate), C204, and cyanide. The redox potential of the ironll ironlll system is altered by complex formation with each of these ligands indeed, the hexacyanoferrate(III) ion, [Fe(CN)6]3. is most readily obtained by oxidation of the corresponding iron(II) complex, because... 

The oxidative behaviour of glycolaldehyde towards hexacyanoferrate(III) in alkaline media has been investigated and a mechanism proposed, which involves an intermediate alkoxide ion. Reactions of tetranitromethane with the luminol and luminol-peroxide radical anions have been shown to contribute substantially to the tetranitromethane reduction in luminol oxidation with hexacyanoferrate(III) in aerated aqueous alkali solutions. The retarding effect of crown ethers on the oxidation of triethylamine by hexacyanoferrate(III) ion has been noted. The influence of ionic strength on the rate constant of oxidation of ascorbic acid by hexacyanofer-rate(III) in acidic media has been investigated. The oxidations of CH2=CHX (where X = CN, CONH2, and C02 ) by alkaline hexacyanoferrate(III) to diols have been studied. ... 

More generally, the method of competition kinetics is used to determine H-atom rate constants. The hexacyanoferrate(III) ion is a suitable solute because reaction (39) can be followed from the decrease in absorbance at 420 nm due to Fe(CN)g (8420 = 104 m mol ). When a second solute is present so that reaction (40) competes with reaction (39), G(-Fe (CN)g ) is given by Eq. (41) ... 

The preparation of film electrodes Prussian blue films are usually prepared by cycling an electrode in a freshly prepared solution containing iron(III) and hexacyanoferrate(III) ions [70-72]. As substrate, mostly platinum is used, sometimes glassy carbon [73] is used, and very frequently ITO electrodes [74] are used because the latter are very useful for electrochromism studies. Similar procedures using solutions containing metal ions and hexacyanoferrate(III) have been used to deposit cobalt hexacyanoferrate [75] and chromium hexacyanoferrate [76, 77]. Crumbliss et al. reported a plasma deposition of iron species from a plasma containing iron pentacarbonyl and ethane, followed by electrochemical derivatization of the deposited iron sites with the help of hexacyanoferrate solutions [78]. 

This process can be described in terms of a heterogeneous reaction in which ferri-cyanide (or hexacyanoferrate(III)) ions, [Fe(CN)g], are formed. At the beginning of the voltammetric peak, the current is controlled by the kinetic of the electron transfer across the electrode/electrolyte barrier so that the current increases somewhat exponentially with the applied potential. The value of the current is controlled 150-200 mV after the voltammetric peak by the diffusion rate of ferrocyanide ions from the solution bulk toward the electrode surface. 

The cyanide ion, CN, is isoelectronic with carbon monoxide and has an extensive chemistry of reaction with transition metals (e.g. the formation of the hexacyanoferrate(III) ion, [Fe(CN)63 ] by reaction with iron(III) in solution) but, unlike CO, it shows a preference for the positive oxidation states of the elements. This is mainly because of its negative charge. 

Hexacyanoferrate(III) ion has been found to be very effective.454 Since overoxidation often takes place in the catalytic process, stoichiometric oxidation generally gives better yields. 

Silver nitrate Hexacyanoferrate (III) Ions, [Fe(CN)6]3 Orange-red precipitate of silver hexacyanoferrate (III), which is soluble in ammonia solution, but not in nitric acid... 

We have already discussed several cases of fast Fe(III) oxidations which occur by a non-bonded electron-transfer mechanism (Tables 13 and 14). One case of a relatively slow reaction, involving the substitution-inert hexacyanoferrate(III) ion, is shown in Table 14 (entry no. 17) and clearly demonstrates the electron-transfer oxidizing properties of this species with respect to easily oxidized aliphatic amines. Whether the same mechanism holds for compounds more resistant to oxidation, such as methylnaphthalenes (Andrulis et al., 1966) remains to be seen (the estimated rate constant at 25°C is ca. 10-7 M l s-1). Generally, hexacyanoferrate(III) seems to be a good non-bonded electron-transfer reagent (for a review, see Rotermund, 1975). 

Potassium hexacyanoferrate(III) solution a dark-blue precipitate is obtained. First hexacyanoferrate(III) ions oxidize iron(II) to iron(III), when hexacyanoferrate(II) is formed ... 

In excess reagent the precipitate dissolves giving a yellow solution, when hexacyanoferrate(III) ions are formed ... 

The precipitate is insoluble in 6m hydrochloric acid. Hexacyanoferrate(III) ions do not react. Oxidizing anions (like chromate, arsenate or nitrite) should be absent, as these oxidize hexacyanoferrate(II) ions in acid medium. 

Dilute acetic acid should be present as well. Hexacyanoferrate(III) ions react only in concentrated solutions, after long standing or heating, to give a dirty-yellow precipitate. Filter paper may reduce some hexacyanoferrate(III) to... 

Benzidine acetate test (DANGER THE REAGENT IS CARCINOGENIC) A neutral or weakly acetic acid solution of a peroxodisulphate converts benzidine into a blue oxidation product. Perborates, percarbonates, and hydrogen peroxide do not react. Chromates, hexacyanoferrate(III) ions, permanganates, and hypohalites react similarly to peroxodisulphates. 

Hydrogen peroxide reduces hexacyanoferrate(III) ions to hexacyano-ferrate(II) ... 

Other reducing agents, e.g. tin(II) chloride, sodium sulphite, sodium thiosulphate, etc. will reduce hexacyanoferrate(III) ions to hexacyanoferrate(II), so that this reaction is not always a reliable test. 

The effect of individual reactants on the tetrahedral and cubic platinum nanoparticles was investigated in order to determine which reactants were responsible for the distortion of the nanoparticles [40]. There was significant dissolution of atoms from the comers and edges of both the tetrahedral and cubic platinum nanoparticles upon exposure to hexacyanoferrate (III) ions. Distorted tetrahedral and cubic platinum nanoparticles became the dominant shape (Fig. 18.3b and d, respectively). The distortion in shape of the nanoparticles was proposed to be due to the cyanide ligand of the hexacyanoferrate (III) ions adsorbing and reacting with the platinum comer and edge atoms of the nanoparticles to form Pt(CN) " complexes. 

Detection of oligosaccharides (e.g., stachyose, raffinose, sucrose, and fructose) in a soybean extract using invertase hydrolysis of p-o-fructo-fructoside to fructose, and further oxidation of this sugar by hexacyanoferrate (III) ion in the presence of fructose dehydrogenase (FDH). This analysis is based on a coimmobilization of invertase from Candida utilis and FDH from Gluconobacter on poly(vinyl alcohol) (PVA) beads and coulometric quantification of the hexacyanoferrate(II) ions formed. 

Thallium forms the monovalent thallium(I) and trivalent thallium(III) ions, the former being of greater analytical importance. Thallium(III) ions are less frequently encountered in solutions, as they tend to hydrolyse in aqueous media, forming thallium(III) hydroxide precipitate. Thallium(I) ions can be oxidized to thallium(III) ions in acid media with permanganate and hexacyanoferrate(III) ions as well as with lead dioxide, chlorine gas, bromine water or aqua regia (but not with concentrated nitric acid). The reduction of thallium(III) ions to thallium(I) is easily effected by tin(II) chloride, sulphurous acid, iron(II) ions, hydroxylamine or ascorbic acid. 

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