Ferric-ferrocyanide complex

Such cyanide complexes are also known for several other metals. All the fer-rocyanide complexes may be considered as the salts of ferrocyanic acid H4Fe(CN)e and ferricyanide complexes are that of ferricyanic acid, H3Fe(CN)e. The iron-cyanide complexes of alkali and alkaline-earth metals are water soluble. These metals form yellow and ruby-red salts with ferro-cyanide and ferricyanide complex anions, respectively. A few of the hexa-cyanoferrate salts have found major commercial applications. Probably, the most important among them is ferric ferrocyanide, FeFe(CN)e, also known as Prussian blue. The names, formulas and the CAS registry numbers of some hexacyanoferrate complexes are given below. Prussian blue and a few other important complexes of this broad class of substances are noted briefly in the following sections ... 

Iron blues, or cyanide iron blues, are complex ferriferrocyanide, generally with ammonium, potassium, or sodium cations. They are most commonly produced by a two-step process. First, ammonium, potassium, or sodium ferrocyanide, M4[Fe(CN)6], is reacted with ferrous sulfate, FeS04, to yield M2Fe[Fe(CN)]6. The latter is digested with hot sulfuric acid and oxidized with sodium chlorate or sodium bichromate to yield the ferric ferrocyanide M(Fe[Fe(CN)6]. ... 

This method for determining reducing sugars (7) is based on the reduction of ferricyanide ions in alkaline solution by a reducing sugar. The ferrocyanide produced can then react with a second mole of ferricyanide producing the ferric-ferrocyanide (Prussian blue) complex. Potassium... 

The above compensating reactions are attractive because of the success of similar schemes in the halide catalysis, but proof in this case is more difficult. Thus it was possible to show in the halide systems that halogen and halide are present simultaneously. Evidence for the presence of ferrous ion in the ferric catalysis would support a similar interpretation. Manchot and Lehmann (44) claimed to have proved that ferrous ion is formed from ferric ion in the presence of peroxide since the addition of <, < -dipyridyl to the mixture resulted in the slow formation of the red ferrous tris-dipyridyl ion Fe(Dipy)3++. However, later work (65,66), which will be discussed when these systems are considered in more detail (IV,6), indicates that the ferrous complex ion may be formed by reduction not of the ferric ion, but of a ferric dipyridyl complex. Similar conclusions on the presence of ferrous ion were drawn by Simon and Haufe (67) from the observation that on addition of ferri-cyanide to the system Prussian blue is formed. This again is ambiguous, since peroxide is known to reduce ferricyanide to ferrocyanide and the latter with ferric ion will of course give Prussian blue (53). 

The hydroferrocyanic derivatives prodnced are in colloidal form. Their floccnlation in wine is accelerated by adding a protein fining agent. Fnr-thermore, precipitation of ferric ferrocyanide at least partially eliminates proteins (Vogt, 1931). This may be advantageous in white wines susceptible to protein turbidity. The precipitation of proteins is not due to the ferrocyanide itself, but rather to an insoluble ferric complex. Indeed, when potassium ferrocyanide is added to a wine containing no iron, no protein turbidity is observed. 

Bronze blue n. One of the names applied to the complex ferric ferrocyanide or iron blues. Leach RH, Pierce RJ, Hickman, EP, Mackenzie MJ, Smith HG (eds) (1993) Printing ink manual, 5th edn. Blueprint, New York. 

The sodium ferrite/ferrate solution is very alkaline and lends to absorb other acid gases such as HCN, CO2. and S02- HCN is a weak acid that reacts with the alkaline solution to form NaCN by a reversible acid/base reaction. Since it is not destroyed (as is H2S) the NaCN builds up in the solution until the vapor pressure of HCN over the solution is high enough to impede absorption. At this point most of the HCN in the feed gas leaves the absorber with the product gas. A small fraction of the HCN will react with solution components to form NaSCN and ferric ferrocyanide (Prussian blue). This fetrocyanide complex is identical to the oxygen carrier employed in the Staatsmijnen-Otto process, and contributes to the oxidation of hydrogen sulfide to elemental sulfur. 

Ferrous ion, iron(II), forms a complex with six cyanide ions, CN- the octahedral complex is called ferrocyanide. Ferric ion, iron(III), forms a complex with six cyanide ions the octahedral complex is called ferricyanide. Write the structural formulas for the ferrocyanide and the ferricyanide complex ions. 

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 nature Of the ions.—In 1814, G. F. Parrst12 found that in the electrolysis of aq. soln. of potassium ferrocyanide the alkali accumulated about the negative pole, and ferric oxide and hydrocyanic acid about the positive pole, and the work of J. F. Daniell and W. A. Miller, and of W. Hittorf (1859), showed that double salts are of two kinds, and that in the one kind the metal is bound as a complex negative ion, and in the other it is the positive ion. For example, in the electrolysis of potassium silver cyanide, KCy.AgCy, W. Hittorf (1859) found that silver was deposited on the cathode, whereas with salts of the type AgN03 it is deposited on the anode. Hence, it was inferred that the salt ionizes KAgCy2=K,- -AgCy2 similarly,... 

A large number of polymeric complexes is known containing ambidentate cyanide bridging groups. These are related to Prussian blue, which is formed by the addition of ferric salts to ferrocyanides ... 

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... 

When a solution of potassium ferrocyanide reacts with rather less than one equivalent of a ferric salt, a blue hydrated precipitate of a-soluble Prussian blue, or ferric potassium ferrocyanide Fe K[Fe (CN)6], is obtained. Now, Hofmann and his co-workers 5 have shown that this precipitate is identical with that prepared under precisely similar conditions by the addition of a ferrous salt to potassium fcrricyanide, although in this case ferrous potassium ferricyanide, Fe K[Fe (CN)6], might be expected. It is therefore assumed that the latter salt is unstable, and, at the moment of formation, undergoes intramolecular rearrangement to the former complex. 

Iron can assume the oxidation states - -2, -f 3, and +6, the last being rare, and represented by only a few compounds, such as potassium ferrate, KoFeO. The oxidation states -f 2 and +3 correspond to the ferrous ion, Fe+ +, and ferric ion, Fe + +, respectively. The ferrous ion is easily oxidized to ferric ion, by air or other oxidizing agents. Both ferrous and ferric ion form complexes, such as the ferrocyanide... 

Complex Cyanides of Iron. Cyanide ion added to a solution of ferrous or ferric ion forms precipitates, which dissolve in excess cyanide to produce the complexes. Yellow crystals of potassium ferrocyanide, K4Fe(CN)(./3H20, are made by heating organic material, such as dried blood, with iron filings and potassium carbonate. The mass produced by the heating is extracted with warm water, and the crystals are made by evaporation of the solution. Potassium ferricyanide, K3Fe(CN), is made as red crystals by oxidation of ferrocyanide. 

So far, we have identified coordination compounds only by their chemical formulas, but names are also useful for many purposes. Some substances were named before their structures were known. Thus, K3[Fe(CN)g] was called potassium fer-ricyanide, and K4[Fe(CN)g] was potassium ferrocyanide [these are complexes of Fe (ferric) and Fe (ferrous) ions, respectively]. These older names are still used conversationally but systematic names are preferred to avoid ambiguity. The definitive source for the naming of inorganic compounds is Nomenclature of Inorganic Chemistry-IUPAC Recommendations 2005 (N. G. Connelly and T. Damhus, Sr., Eds. Royal Society of Chemistry, 2005). 

Notes on the addition reactions of nitric oxide. Nitric oxide is an odd molecule, with an odd number of electrons. Probably because of this fact it is unusually active in forming coordination compounds. Examples of such coordination compounds and complex ions are (FeNO)++, [Co(NH3)6NO]++, CuNOCls-, FeNOCls, AINOCI3, Fe(CN)BNO", and the nitrosyl carbonyls, such as Co(CO)3NO. Many of these complexes are unstable and decompose on heating. They appear to be formed by the donation of either one or three electrons from the NO molecule thus in the nitroprusside ion, Fe(CN)5NO , produced by the action of nitric acid on a ferrocyanide, the nitric oxide is considered to contribute three electrons to the iron atom, leaving the latter in the ferrous rather than the ferric condition. Likewise the existence... 

It should also be taken into account that only Fe + ions react with ferrocyanide, and that most of the ferric iron Fe is combined in soluble complexes with organic acids. As the ferrocyanide reacts with the Fe + ions, the soluble complexes break down to reestablish an equilibrium, generating new Fe + ions that react in turn. This series of reactions may continue for several hours, or even days. Reaction time is longest at high pH, as larger quantities of soluble complexes are present (Figure 4.2). 

The reaction with potassium ferrocyanide is not nearly as slow when the iron is in ferrous form, as less ferrous iron is combined in complexes than ferric iron. It is, therefore, clear that wine should be in a reduced state when it is treated with ferrocyanide. Prior treatment (24 hours before) with ascorbic acid (5-6 g/hl) considerably improves effectiveness. 

Blue Ultramarine blue pigments are sodium/aluminum sulfide-silicate complexes. They are used in PP and HOPE, but they have poor resistance to acidic and alkaline outdoor environments. "Cobalt blue" (cobalt aluminate) is a higher-cost, more weatherable alternative. Ferric ammonium ferrocyanide "iron blue" has been used in LDPE bags, for example. 

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