Prussian blue formation

Sodium ferrocyanide (IOH2O) [13601-19-9] M 484.1, m 50-80 (ioses lOHjO), 435 (dec), d 1.46, pK 2.57, pK4 4.35 (for ferrocyanide). Crystd from hot water (0.7mL/g), until free of ferricyanide as shown by absence of Prussian Blue formation with ferrous sulfate soln. 

All of the [Fe(CN) J4- salts may be considered salts of ferrocyanic acid or tetrahydrogen hexakiscyanoferrate [17126-47-5], H4[Fe(CN)J, a strongly acidic, air-sensitive compound. It is soluble in water and alcohol but is insoluble in ether. It can be prepared by precipitation of an etherate by adding ether to a solution of [Fe(CN) J4"" that was acidified with concentrated sulfuric acid. Removal of the ether of solvation affords a white powder which is stable when dry but slowly turns blue in moist air because of Prussian Blue formation. 

Hydrochloric acid should not be used for acidifying the alkaline solution since the yellow colour, due to the ferric chloride formed, causes the Prussian blue to appear greenish. For the same reason, ferric chloride should not be added—as is frequently recommended a sufficient concentration of ferric ions is produced by atmospheric oxidation of the hot alkaline solution. The addition of a little dfiute potassium fluoride solution may be advantageous in assisting the formation of Prussian blue in a readily filterable form. 

Prussian Blue. Reaction of [Fe(CN)3] with an excess of aqueous h on(Ill) produces the finely divided, intensely blue precipitate Pmssian Blue [1403843-8] (tetrairon(Ill) tris(hexakiscyanoferrate)), Fe4[Fe(CN)3]. Pmssian Blue is identical to Turnbull s Blue, the name which originally was given to the material produced by reaction of [Fe(CN)3] with excess aqueous h on(Il). The soHd contains or has absorbed on its surface a large and variable number of water molecules, potassium ions (if present in the reaction), and h on(Ill) oxide. The h on(Il) centers are low spin and diamagnetic h on(Ill) centers are high spin. Variations of composition and properties result from variations in reaction conditions. Rapid precipitation in the presence of potassium ion affords a colloidal suspension of Pmssian Blue [25869-98-1] which has the approximate composition KFe[Fe(CN)3]. Pmssian Blue compounds are used as pigments in inks and paints and its formation on sensitized paper is utilized in the production of blueprints. 

The industrial production of Prussian blue is based on the reaction in aqueous solution of sodium hexacyanoferrate(n), Na4Fe(CN)6, with iron(n) sulfate, FeS04-7H20 in the presence of an ammonium salt, which results initially in the formation of the colourless insoluble iron(n) hexa-cyanoferrate(n) (Berlin white). Prussian blue is generated by subsequent oxidation with a dichromate or chlorate. 

Following a published procedure for converting substituted anilines to isatins by reaction with chloral hydrate and hydroxylamine [1], it was noticed that at the end of the first stage (formation of an isonitrosoacetanilide), the odour of hydrogen cyanide was present, and this was confirmed by a Prussian blue test [2], In related work, concentrations of 100-200 ppm of hydrogren cyanide were found [3]. A mechanism for its formation from chloral hydrate and hydroxylamine was proposed [2], and the need for appropriate precautions was stressed [2,3],... 

The fact that Prussian blue is indeed ferric ferrocyanide (Fe4in[Fen(CN)6]3) with iron(III) atom coordinated to nitrogen and iron(II) atom coordinated to carbon has been established by spectroscopic investigations [4], Prussian blue can be synthesized chemically by the mixing of ferric (ferrous) and hexacyanoferrate ions with different oxidation state of iron atoms either Fe3+ + [Fen(CN)6]4 or Fe2+ + [Fem(CN)6]3. After mixing, an immediate formation of the dark blue colloid is observed. However, the mixed solutions of ferric (ferrous) and hexacyanoferrate ions with the same oxidation state of iron atoms are apparently stable. 

Except for deposition of Prussian blue from the mixture of ferric and ferricya-nide ions, its electrosynthesis from the single ferricyanide solution is reported [13]. Ferricyanide ions are not extremely stable even in aqueous solution, which is noticed in the change of color after a few days of storage. Thus, the coordination sphere can be destroyed also in the course of electrochemical reactions. The mentioned processes may lead to formation of ferric-ferricyanide complex or free ferric ions. The reduction of the resulting mixture leads to the formation of Prussian blue. 

Excess oils and hydrocarbons in the sulfur plant feed can readily darken the sulfur, minimizing its sales value. Ammonia can cause fouling of the Claus catalyst beds. Cyanides have a tendency to polymerize, causing significant problems with the formation of Prussian blue. Organic forms of sulfur are not so readily reacted in low-temperature Claus beds and may cause problems in achieving the desired sulfur plant efficiency. Addi-... 

If Prussian blue can be used to detect cyanide, which is one of its ingredients, why not iron, another one There is no reason why it can t. When the right reagent containing cyanide is added to a sample containing ferric ions, Prussian blue forms readily. This is the basis of a laboratory test for detecting iron deposits in the human liver. The formation of Prussian blue upon addition of a reagent to the biopsy sample indicates iron overload, a potentially serious condition. 

This acid was isolated by Winterl (1790), Buchholz (1798) and Rink (1804).4 Its potassium salt was first prepared by Porret in 1808 by boiling potassium sulphide solution with Prussian blue. The composition of the acid was first determined by Berzelius in 1820. The question of the formation of the acid in animals has been the subject of investigation by Dezani and others, but their results have led to the conclusion that the acid is not produced in the animal organism, but is purely exogenetic.6... 

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