Prussian blue

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For the musical duo, see Prussian Blue.
Prussian blue
A sample of Prussian blue
IUPAC name
Iron(II,III) hexacyanoferrate(II,III)
Other names
ferric ferrocyanide, iron(III) ferrocyanide, iron(III) hexacyanoferrate(II), ferric hexacyanoferrate (German: Preußischblau and Berliner Blau, Berlin blue, Parisian blue
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 14038-43-8 YesY
RTECS number V03AB31
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula Fe4[Fe(CN)6]3
Molar mass 859.23 g/mol
Appearance blue solid
Solubility in water insoluble
style="background: #F8EABA; text-align: center;" colspan="2" | Pharmacology
Routes of
administration 		Oral
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS MSDS prussian blue
EU Index Not listed
Flash point Non-flammable
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related compounds Sodium ferrocyanide
Potassium ferrocyanide
Potassium ferricyanide
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
Prussian Blue
<imagemap>Image:Gtk-dialog-info.svg|16px|About these coordinates

rect 0 0 50 50 About these coordinates desc none</imagemap>— Color coordinates —

Hex triplet #003153
RGBB (r, g, b) (0, 49, 83)
HSV (h, s, v) (205°, 100%, 43%)
Source [Unsourced]
B: Normalized to [0–255] (byte)

Prussian blue is a dark blue pigment – one of the first synthetic pigments – which was synthesized for the first time in Berlin around the year 1706.[1][2] It was named "Preußisch blau" and "Berlinisch Blau" in 1709 by its first trader.[3] Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue.

The key colored substance in Prussian blue pigment is an insoluble inorganic compound composed of iron and cyanide ions, with water. It has the idealized formula Fe7(CN)18 with 14 to 16 H2O. The pigment may also contain variable amounts of other ions. The color of the pigment depends partly on the size of precipitated particles formed when it precipitates from addition of iron(III) to soluble ferrocyanide.

With several other names (see table to right), this dark blue solid is commonly abbreviated "PB."[4] Because it is easily synthesized in impure form, it is the object of instructional experiments. It has a complicated chemistry, however, that has led to extensive speculation on its structure.

Prussian blue is a common pigment, used in paints, and it is the traditional "blue" in blueprints. It has been used as an antidote for certain kinds of heavy metal poisoning.

History

Prussian blue was probably synthesized for the first time by the paint maker Diesbach in Berlin around the year 1706.[5] Most historical sources do not mention a first name of Diesbach. Only Berger refers to him as Johann Jacob Diesbach.[6] The pigment was an important topic in the letters exchanged between Johann Leonhard Frisch and the president of the Royal Academy of Sciences, Gottfried Wilhelm Leibniz, between 1708 and 1716.[7] It is first mentioned in a letter written by Frisch to Leibniz, from March 31, 1708. Not later than 1708, Frisch began to promote and sell the pigment across Europe. By August 1709, the pigment had been termed "Preussisch blau"; by November 1709, the German name "Berlinisch Blau" had been used for the first time by Frisch. Frisch himself is the author of the first known publication of Prussian blue in the paper Notitia Coerulei Berolinensis nuper inventi in 1710, as can be deduced from his letters. Diesbach had been working for Frisch since about 1701.

In 1731, Georg Ernst Stahl published a story dealing with the incidence of the first synthesis of Prussian blue.[8] The story involves not only Diesbach but also Johann Konrad Dippel. Diesbach was attempting to create a red lake pigment from cochineal but obtained the blue instead as a result of the contaminated potash he was using. He borrowed the potash from Dippel, who had used it to produce his "animal oil". No other known historical source mentions Dippel in this context. It is therefore difficult to judge the reliability of this story today. In 1724, the recipe was finally published by Woodward.[9]

To date, the painting "Entombment of Christ", dated 1709 by Pieter van der Werff (Picture Gallery, Sanssouci, Potsdam) is the oldest known painting where Prussian blue has been used. Around 1710, painters at the Prussian court were already using the pigment. At around the same time, Prussian blue arrived in Paris, where Antoine Watteau and later his successors Nicolas Lancret and Jean-Baptiste Pater used it in their paintings.[10]

File:The Great Wave off Kanagawa.jpg
"The Great Wave off Kanagawa" by Hokusai, a famous artwork which makes extensive use of Prussian blue.

This Prussian blue pigment is significant since it was the first stable and relatively lightfast blue pigment to be widely used following the loss of knowledge regarding the synthesis of Egyptian Blue. European painters had previously used a number of pigments such as indigo dye, smalt, and Tyrian purple, which tend to fade, and the extremely expensive ultramarine made from lapis lazuli. Japanese painters and woodblock print artists likewise did not have access to a long-lasting blue pigment until they began to import Prussian blue from Europe. Cobalt blue has been used extensively by Chinese artists in blue and white porcelains for centuries, and was introduced to Europe in the 18th century.

In 1752 the French chemist Pierre J. Macquer made the important step of showing the Prussian blue could be reduced to a salt of iron, and a new acid, previously unknown, which could be used to reconstitute the dye. The new acid, hydrogen cyanide, first isolated from Prussian blue in pure form and characterized about 1783 by the Swedish chemist Carl Wilhelm Scheele, was eventually given the name Blausäure (literally "Blue acid") because of its derivation from Prussian blue, and in English became known popularly as Prussic acid. Prussian blue would also give the name to the cyanide family of compounds, which are named from the Greek word for "blue," because they were first isolated from Prussian blue.

Properties

Structure

Prussian blue has a soluble form, K[FeIIIFeII(CN)6], and an insoluble form, FeIII4[FeII(CN)6]3.xH2O.

Despite being one of the oldest known synthetic compounds, the composition of Prussian blue was uncertain until recently. The precise identification of Prussian blue was complicated by three factors:

  1. Prussian blue is extremely insoluble but also tends to form colloids;
  2. Traditional syntheses tend to afford impure compositions; and
  3. Even pure Prussian blue is structurally complex, defying routine crystallographic analysis.

The chemical formula of Prussian blue is Fe7(CN)18.xH2O where x = 14-16. [11] The determination of the structure and the formula resulted from decades of study using IR spectroscopy, Moessbauer spectroscopy, X-ray crystallography, and neutron crystallography. Since X-ray diffraction cannot distinguish carbon from nitrogen, the location of these lighter elements is deduced by spectroscopic means as well as distances from the iron atom centers.

Researchers concluded that the framework consists of sequences of Fe(II)-C-N-Fe(III), with Fe(II)-carbon distances of 1.92 Å (0.192 nanometers) and Fe(III)-nitrogen distances of 2.03 Å (0.203 nanometers). The Fe(II) centers, which are low spin, are surrounded by six carbon ligands. The Fe(III) centers, which are high spin, are surrounded on average by 4.5 nitrogen atom centers and 1.5 oxygen atom centers (the oxygen from water).[12] The ideal unit cell contains six coordinated water molecules around the Fe(III) atom and eight uncoordinated (interstitial) water molecules. [11]

The composition is notoriously variable due to the presence of lattice defects, allowing it to be hydrated to various degrees as water molecules are incorporated into the structure to occupy four cation vacancies. The variability of Prussian blue's composition is attributable to its low solubility, which leads to its rapid precipitation without the time to achieve full equilibrium between solid and liquid.

Turnbull's blue

File:HexacyanidoferratIII 2.svg
Ferricyanide ion

"Prussian blue" (PB) can be obtained by the addition of Fe(III) salts to a solution of [Fe(CN)6]4− (ferrocyanide). "Turnbull's Blue" (TB) arises by the related reaction where the valences on the iron precursors are switched, i.e. the addition of a Fe(II) salt to a solution of [Fe(CN)6]3- (ferricyanide). TB is also an intensely blue colored material, whose hue was claimed to differ from that of PB.

It has been shown by means of X-ray diffraction pattern and electron diffraction pattern methods, that the compositions of PB and TB are identical. [13] [14] This may be explained by the following equilibrium reaction:

<math>\mathrm{Fe^{2+} + [Fe(CN)_6]^{3-} \ \rightleftharpoons \ Fe^{3+} + [Fe(CN)_6]^{4-}}</math>

The predominating reaction to the right side results in prussian blue:

K+ + Fe3+ + [FeII(CN)6]4- → KFeIII[FeII(CN)6] [15]

This all means that Turnbull's blue is just another way to produce Prussian blue. It is now appreciated that TB and PB are the same because of the rapidity of electron exchange through a Fe-CN-Fe linkage. The differences in the colors for TB and PB reflect subtle differences in the method of precipitation, which strongly affects particle size and impurity content.

Solubility

PB is insoluble, but it tends to form such small crystallites that colloids are common. These colloids behave like solutions, for example they pass through fine filters. "Soluble" forms of PB tend toward compositions with the approximate formula KFe[Fe(CN)6].[4]

Color

Prussian blue is strongly colored and tends towards black and dark purple when mixed into oil paints. The exact hue depends on the method of preparation, which dictates the particle size. The intense blue color of Prussian blue is associated with the energy of the transfer of electrons from Fe(II) to Fe(III). Many such mixed-valence compounds absorb certain wavelengths of visible light. In this case, orange-red light around 680 nanometers in wavelength is absorbed, and the transmitted light appears blue as a result.

Other properties

Prussian blue and its analogs have been extensively studied by inorganic chemists and solid-state physicists because of its unusual properties.

  • It undergoes intervalence charge transfer. Although intervalence charge transfer is well-understood today, Prussian blue was the subject of intense study when the phenomenon was discovered.
  • It is electrochromic—changing from blue to colorless upon reduction. This change is caused by reduction of the Fe(III) to Fe(II) eliminating the intervalence charge transfer that causes Prussian blue's color.

Despite the presence of the cyanide ion, Prussian blue is not especially toxic because the cyanide groups are tightly bound. Other cyanometalates are similarly stable with low toxicity. Treatment with acids, however, can liberate hydrogen cyanide which is extremely toxic, as discussed in the article on cyanide.

Production

Prussian blue, such as that in inks, is prepared by adding a solution containing iron(III) chloride to a solution of potassium ferrocyanide. During the course of the addition the solution thickens visibly and the color changes immediately to the characteristic blue of Prussian blue.

Uses

Prussian blue in medicine

Prussian blue's ability to incorporate cations that have one unit of positive charge makes it useful as a sequestering agent for certain heavy-metals ions. Pharmaceutical-grade Prussian blue in particular is used for patients who have ingested thallium or radioactive cesium. According to the International Atomic Energy Agency, an adult male can eat at least 10 grams of Prussian blue per day without any serious harm. The U.S. Food and Drug Administration (FDA) has determined that the "500 mg Prussian blue capsules, when manufactured under the conditions of an approved New Drug Application (NDA), can be found safe and effective therapy" in certain poisoning cases.[16] Radiogardase® (Prussian blue insoluble capsules) is a commercial product for the removal of cesium-137 from the bloodstream.[17]

As a laboratory histopathology stain for iron

Prussian blue is a common histopathology stain used by pathologists to detect the presence of iron in biopsy specimens, such as in bone marrow samples. The original stain formula, known historically (1867) as "Perls' Prussian blue" after its inventor, German pathologist Max Perls (1843-1881), used separate solutions of potassium ferrocyanide and acid to stain tissue (these are now used combined, just before staining). Iron deposits in tissue then form the purple Prussian blue dye in place, and are visualized as blue or purple deposits.[18] The formula is also known as Perls Prussian blue and (incorrectly) as Perl's Prussian blue.

As a pigment

Prussian blue is the coloring agent used in engineer's blue and the pigment formed on cyanotypes - giving them their common name blueprints. Certain crayons were once colored with Prussian blue (later relabeled Midnight Blue). It is also a popular pigment in paints.

Clothes laundering

Colloids derived from Prussian blue are the basis for laundry bluing.

By machinists and toolmakers

Prussian blue in oil paint is the traditional material used for spotting metal surfaces such as surface plates and bearings for hand scraping. A thin layer of non-drying paste is applied to a reference surface and transfers to the high spots of the workpiece. The toolmaker then scrapes, stones, or otherwise removes the high spots. Prussian blue is preferable because it will not abrade the extremely precise reference surfaces as many ground pigments may.

Chemical Assays

Prussian blue is formed in the Prussian blue assay for total phenols. Samples and phenolic standards are given acidic ferric chloride and ferricyanide which is reduced to ferrocyanide by the phenols. The ferric chloride and ferrocyanide react to form Prussian blue. Comparing the absorbance at 700 nm of the samples to the standards allows for the determination of total phenols.[19]

References

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See also

External links

Shades of blue
Air Force blueAlice blueAzureBaby blueBleu de FranceBlueBondi blueBrandeis blueCambridge BlueCarolina blue
          
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IrisLight blueMajorelle BlueMaya blueMidnight blueNavy blueNon-photo bluePalatinate bluePeriwinklePersian blue
          
Powder bluePrussian blueRoyal blueSapphireSky blueSteel blueTealTiffany BlueTufts BlueUCLA Blue
          
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The samples shown above are only indicative.
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    de:Berliner Blau es:Azul de Prusia fr:Bleu de Prusse ko:프러시안 블루 it:Blu di Prussia he:כחול פרוסי la:Caeruleus Berolinus lt:Karaliaučiaus mėlis nl:Pruisisch blauw ja:紺青 no:Preussisk blå pl:Błękit pruski (pigment) pt:Azul da prússia ro:Albastru de Berlin ru:Берлинская лазурь simple:Prussian blue sv:Berlinerblått zh-yue:洋靛

    zh:普鲁士蓝
    1. ↑ J.Bartoll, B. Jackisch, M. Most, E. Wenders de Calisse, C. M. Vogtherr: Early Prussian Blue. Blue and green pigments in the paintings by Watteau, Lancret and Pater in the collection of Frederick II of Prussia In: TECHNE 25, 2007, S. 39-46
    2. ↑ Jens Bartoll. "The early use of prussian blue in paintings" (PDF). 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008. Retrieved 2010-01-22. 
    3. ↑ J. L. Frisch: Briefwechsel mit Gottfried Wilhelm Leibniz L. H. Fischer (ed.), Berlin, Stankiewicz Buchdruck, 1896, reprint Hildesheim/New York: Georg Olms Verlag, 1976
    4. ↑ 4.0 4.1 *Dunbar, K. R. and Heintz, R. A., "Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives", Progress in Inorganic Chemistry, 1997, 45, 283-391.
    5. ↑ J.Bartoll, B. Jackisch, M. Most, E. Wenders de Calisse, C. M. Vogtherr: Early Prussian Blue. Blue and green pigments in the paintings by Watteau, Lancret and Pater in the collection of Frederick II of Prussia In: TECHNE 25, 2007, S. 39-46
    6. ↑ J. E. Berger: Kerrn aller Fridrichs=Städtschen Begebenheiten Manuskript, Berlin, ca.1730 (Berlin, Staatsbibliothek zu Berlin – Preußischer Kulturbesitz, Handschriftenabteilung, Ms. Boruss. quart. 124)
    7. ↑ J. L. Frisch: Briefwechsel mit Gottfried Wilhelm Leibniz L. H. Fischer (ed.), Berlin, Stankiewicz Buchdruck, 1896, reprint Hildesheim/New York: Georg Olms Verlag, 1976
    8. ↑ G. E. Stahl: Experimenta, Observationes, Animadversiones CCC Numero, Chymicae et Physicae, Berlin, 1731
    9. ↑ J. Woodward: Praeparatio coerulei Prussiaci es Germanica missa in: Philosophical Transactions, London, 33, 1726
    10. ↑ J.Bartoll, B. Jackisch, M. Most, E. Wenders de Calisse, C. M. Vogtherr: Early Prussian Blue. Blue and green pigments in the paintings by Watteau, Lancret and Pater in the collection of Frederick II of Prussia In: TECHNE 25, 2007, S. 39-46
    11. ↑ 11.0 11.1 Fikru Tafesse: Comparative Studies on Prussian Blue or Diaquatetraamine-cobalt(III) Promoted Hydrolysis of 4-Nitrophenylphosphate in Microemulsions Int. J. Mol. Sci. 2003, 4, p.367
    12. ↑ S. Choudhury; et al. (2002). "Crystallization of Prussian Blue Analogues at the Air−Water Interface Using an Octadecylamine Monolayer as a Template". Langmuir. 18: 7409–7414. doi:10.1021/la0201873. 
    13. ↑ Toru Ozeki, Koichi Matsumoto, Seiichiro Hikime: Photoacoustic spectra of prussian blue and photochemical reaction of ferric ferricyanide Anal. Chem., 1984, 56 (14), pp. 2819–2822. doi:10.1021/ac00278a041
    14. ↑ Izatt, et al. Calorimetric study of Prussian blue and Turnbull's blue formation Inorg. Chem., 1970, 9 (9), pp. 2019–2021. doi:10.1021/ic50091a012
    15. ↑ Egon Wiberg,Nils Wiberg,Arnold Frederick Holleman: Inorganic chemistry Academic Press, 2001; Google books
    16. ↑ "Questions and Answers on Prussian Blue". Retrieved 2009-06-06. 
    17. ↑ Heyltex Corporation - Toxicology
    18. ↑ Formula for Perls' Prussian blue stain. Accessed April 2, 2009.
    19. ↑ Tannin ChemistryPDF (1.41 MB)Accessed December 19, 2009
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