Potassium ferrocyanide, reaction with

Fluorination with fluorine produces copper(ll) fluoride, CuF2. Adding potassium ferrocyanide to CuCb aqueous solution precipitates out reddish brown cupric ferrocyanide. Reaction with caustic soda forms blue cupric... 

As mentioned earlier, potassium ferrocyanide reacts with Fe to produce Prussian blue. On the other hand, reaction with Fe2+ first gives a white precipitate of K2Feii[Feii(CN)6], which can readily oxidize in the air forming Prussian blue. 

Haleys Dialyzed Iron and Related Methods, Hyaluronic acid was said by Hale to combine with dialyzed iron in acetic acid solution 89), After the sections were rinsed, the classical HCl - potassium ferrocyanide reaction was used to color (as Prussian blue) the sites of iron-binding. The need for fixatives that would not dissolve hyaluronic acid was emphasized. The specificity was established by exposing duplicate portions of tissue to streptococcal hyaluronidase, presumable filtrates, before staining. This prevented coloration of hyaluronic acid but not that of other acidic carbohydrates. 

Sodium Nitroprusside, Na2Fe(CN)5NO (22.6.7) It is synthesized by successive reactions including the reaction of potassium ferrocyanide with nitric acid, which forms potassium nitroprusside (22.6.5), which is further transformed to copper nitroprusside (22.6.6), and reaction of this with sodium carbonate gives sodium nitroprusside (22.6.7). 

Copper(ll) nitrate, being an oxidizing agent, can undergo violent reactions with readily oxidizahle substances. Reaction with acetic anhydride is violent, and heating with potassium or ammonium ferrocyanide at 220°C may cause an explosion. It can ignite paper on prolonged contact. 

Alkylation of Alkali Metal Cyanides by Alkyl Halides Activated in the a-Posi-tion by a Double Bond. When a mixture consisting of 4 to 8 moles of an alkyl halide activated in the apposition by a double bond is heated with 1 mole of alkali metal ferrocyanide, several alkylation products of the ferrocyanide anion can be isolated from the reaction mixture (12). The relative proportions of the tetra-, penta-, and hexaalkylated complexes can be varied by varying the alkyl halide to ferrocyanide ratio and the time of reaction. When potassium ferrocyanide is alkylated with benzyl bromide at a ratio of 4 alkyl halides to ferrocyanide anion, short reaction times favor the tetraalkylated complex an 8 to 1 ratio and long reaction times favor the hexaalkylated complex of the alkylating agents tested benzyl bromide provided the fastest alkylation ... 

A typical reaction profile is summarized in Figure 2 for the reaction of potassium ferrocyanide with benzyl bromide. At the initial stages of the reaction the reaction mixture consists primarily of the tetra- and pentaalkylated complexes when the maximum conversion of 92% to isonitrile complexes is reached, after 48 hours, the hexaalkylated product begins to appear. 

Figure 2 Reaction of potassium ferrocyanide with benzyl...

Transalkylation Reaction. The alkylation reaction of potassium ferrocyanide with alkyl bromides activated at the a-carbon by a double bond (14) gave in each case good conversions to the corresponding isonitrile complexes. Since this method is limited to alkyl halides activated at the Qj-carbon by a double bond, it was of interest to develop a general method for the preparation of aliphatic isonitrile complexes. 

Perhaps the most spectacular secret ink is Prussian blue, which forms by means of a chemical reaction between ferric sulfate and potassium ferrocyanide. Generally, a message written with ferric sulfate solution will be revealed when it is sprayed with ferrocyanide. A spy can soak fabric with each of these solutions and transport secret information without detection. During World War ii a German spy named George Vaux Bacon made notations on his socks and cloth buttons with the secret ink reagents. He, too, was caught and executed. 

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 somewhat similar method of cyanide preparation is applicable in the aromatic series aromatic sulphonic acid potassium salts, on fusion with potassium cyanide or potassium ferrocyanide, yield aromatic nitriles. The reaction can be extended to derivatives of pyridine. 

The redox reaction of the ferrocene moiety in a 6-(ferrocenyl)hexanethiol-hexanethiol (FcCgSH Q,SH, 1 20) mixed monolayer has been studied in the presence of potassium ferrocyanide as reducing agent. Thus, the ferrocenium formed at anodic potentials is reduced to ferrocene by the ferrocyanide in solution and the whole process becomes a surface catalytic reaction, in agreement with the following reaction scheme ... 

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 ... 

Cyanides.—The attempts to prepare cyanides by the direct or indirect union of nitrogen and carbon must be mentioned here they are of importance particularly for the problem of utilizing atmospheric nitrogen. Since the reactions take place at a high temperature, we can also make use of electrically produced heat, as suggested by Readmann 2 but in his process— a mixture of oxides or carbonates of alkalies, or earthy alkalies, with carbon is heated in the voltaic arc between two carbon points in the presence of nitrogen—electrolysis occurs as an important factor. The conditions are similar in his attempts, undertaken with Gilmour,3 to prepare potassium ferrocyanide. 

Osmyl Tetra-ammine Chloride, 0sO2(NH3)4Cl2, and is obtained as a yellow, crystalline precipitate when ammonium chloride is added to aqueous potassium osinate.6 It is but slightly soluble in water, and boiling water decomposes it into osmium tetroxide and osmium di-ammine hydroxide. Its solution gives a violet coloration with potassium ferrocyanide, a reaction that may be utilised for the detection of osmium.7 It is insoluble in alcohol and in hydrochloric acid. When heated it decomposes completely, yielding a mass of spongy osmium. 

The old commercial method of preparing the salt lay in heating nitrogenous material, such as horn, wool, feathers, blood, etc., with potash and iron turnings. The mass was ultimately heated to fusion to complete the reaction, cooled, and extracted with boiling water. The solution contained potassium ferrocyanide, thiocyanate, carbonate, and sulphide. The first-named was crystallised out, but the yield was seldom more than 20 per cent, of the quantity theoretically obtainable from the nitrogen content of the organic material consumed. 

When potassium ferrocyanide is heated with concentrated sulphuric acid, carbon monoxide is evolved. This reaction has been known for many years,4 but it was not until 1900 that the reaction was thoroughly investigated.5... 

If a little water is present, carbon monoxide is readily formed on warming, the best result being attained with acid of concentration corresponding to H2S04,2H20, when dry anhydrous potassium ferrocyanide is employed the reaction is then complete at 180° C. —6... 

The reaction velocity has been studied 9 at 90° C., with interesting results. The velocity at first decreases slightly, then increases rapidly to a maximum, after attaining which it falls again. The reason for the increased velocity lies in the autocatalytic action of the potassium ferrocyanide produced during the reaction. 

Hydrogen nitroso ferricyanide or nitroprussic acid, H2[Fe(CN)5NOJ, is obtained by decomposition of the silver salt with hydrochloric acid or by the action of dilute sulphuric acid upon the barium salt. It is also formed when nitric oxide is bubbled through an acidified solution of potassium ferrocyanide.4 The reaction proceeds in two stages, namely, (a) oxidation to the ferricyanide, and (b) substitution of the cyanogen radicle by NO —... 

It may be conveniently prepared by heating potassium ferrocyanide with 50 per cent, nitric acid solution on a water-bath until a drop of the solution gives no colour with ferrous sulphate. The whole is cooled, the liquid poured from the precipitate, neutralised with sodium carbonate, and taken to dryness. Extraction with water, filtration from the insoluble iron compounds, and crystallisation from the clear aqueous solution yields the salt in ruby-coloured, rhombic prisms. The reactions involved may be represented as follows —... 

Wet Tests.—The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate—Turnbull s blue—is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not d troyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present. 

The fusion of alkali arylsulfonates with potassium cyanide forms aromatic nitriles by a replacement of the sulfo group. For the most part, the yields are low, although the reaction has been applied successfully in the preparation of naphthonitriles and cyanopyridines. Sometimes potassium ferrocyanide is substituted for the alkali cyanide with better results. Ten isomeric cyanonaphthalenesulfonates have been converted to the dinitriles by fusion with this reagent in yields ranging from 8% to 75%. Migration of the cyano group from the beta to the alpha position has been observed in the formation of these Compounds. ... 

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