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Structural formula
Structure of dicyan
Surname Dicyan
other names
  • Cyan
  • Cyanogen
  • Oxalic acid dinitrile
  • Oxalyl dinitrile
  • Cyan
Molecular formula (CN) 2
Brief description

colorless gas with a pungent bitter almond smell

External identifiers / databases
CAS number 460-19-5
EC number 207-306-5
ECHA InfoCard 100.006.643
PubChem 9999
ChemSpider 9605
Wikidata Q421724
Molar mass 52.04 g mol −1
Physical state



0.95 g cm −3 (liquid, −21 ° C )
2.38 g l −1 (gas, 0 ° C, 1013 mbar)

Melting point

−27.83 ° C

boiling point

−21.15 ° C

Vapor pressure

0.49 M Pa (20 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 04 - gas bottle 06 - Toxic or very toxic 09 - Dangerous for the environment


H and P phrases H: 220-280-330-319-335-410
P: 210-260-281-377-381-304 + 340-315-403-405

DFG / Switzerland: 5 ml m −3 or 11 mg m −3

Toxicological data

350 ppm 60 min −1 ( LC 50ratinh. )

Thermodynamic properties
ΔH f 0

306.7 kJ / mol

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Dicyan is a poisonous, gaseous chemical compound. It consists of two cyanide groups linked by a single bond . It is also known as cyan or cyan for short .

History and occurrence

Dicyan was probably synthesized for the first time by Carl Wilhelm Scheele in 1782 when he was investigating hydrogen cyanide. It was definitely synthesized in 1802 when cyanogen chloride was produced. Even before the first synthesis of an organic substance, generally recognized as such ( urea , Friedrich Wöhler , 1828), F. Wöhler succeeded in synthesizing oxalic acid by hydrolyzing dicyan (1824).

Dicyan was detected in 1910 in the tail of Halley's comet, which was then returning .

Extraction and presentation

In the laboratory, dicyan is produced by heating mercury (II) cyanide or silver cyanide , the complex salts dicyanidoargentate (I), K [Ag (CN) 2 ] and tetracyanidomercurate (II) K 2 [Hg (CN) 4 ] behave in the same way.

In the laboratory, the representation by dropping a concentrated sodium or potassium cyanide solution on finely powdered copper sulfate or a concentrated solution of the same is also used:

Copper (II) salts can also be used as oxidizing agents. In the presence of cyanide salts , these are oxidized to dicyan and the copper is reduced to tetracyano-cuprate (I) .

Gold (III) salts in water also react as strong oxidizing agents towards cyanides with the formation of potassium dicyanido aurate (I) .

Dicyan is formed in all electrolyses of cyanides or cyanido complexes by anodic oxidation at pH 4–6 on inert platinum electrodes, the mechanism is similar to that of Kolbe electrolysis .

Technically, it is determined by the oxidation recovered by cyanide, usually with chlorine in an activated silica - catalyst or nitrogen dioxide to copper salts is used. Dicyan is also formed from nitrogen and ethylene under the action of electrical discharges.


Dicyan is a linear molecule with a bond length of 116.3  pm (C – N) or 139.3 pm (C – C). The C – C bond, with a dissociation energy of 603 (21) kJ / mol, is the strongest so far determined C – C single bond.

Dicyan is a colorless and poisonous, pungent-sweet smelling gas with a boiling point of −21 ° C. It burns with a very hot (4800 K in pure oxygen), red-violet flame. Dicyan behaves chemically similar to a halogen and is therefore referred to as a pseudohalogen .

It dissolves little in water and slowly disproportionates to hydrogen cyanide and cyanic acid ; their salts are formed in alkaline solution.

Dicyan already polymerizes in sunlight or when heated to solid, brown-black paracyan .

Dicyan forms easily flammable mixtures with air. The explosion range is between 3.9% by volume (84 g / m 3 ) as the lower explosion limit (LEL) and 36.6% by volume (790 g / m 3 ) as the upper explosion limit (UEL).

The critical point is at a temperature of 126.5 ° C and a critical pressure of 5.98  MPa .

The enthalpy of vaporization of dicyan at a pressure of 1013 hPa is 448 kJ / kg.

Individual evidence

  1. a b entry on dicyan. In: Römpp Online . Georg Thieme Verlag, accessed on July 16, 2014.
  2. a b c d e f g h i j Entry for CAS no. 460-19-5 in the GESTIS substance database of the IFA , accessed on January 3, 2014(JavaScript required) .
  3. Entry on Oxalonitrile in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  4. Swiss Accident Insurance Fund (Suva): Limits - Current MAK and BAT values (search for 460-19-5 or Dicyan ), accessed on November 2, 2015.
  5. Entry on dicyan in the ChemIDplus database of the United States National Library of Medicine (NLM)
  6. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-23.
  7. ^ Burckhard Frank: 250 years of chemistry in Göttingen . In: Hans-Heinrich Voigt (Ed.): Natural sciences in Göttingen. A series of lectures . Vandenhoeck + Ruprecht Gm, Göttingen 1988, ISBN 3-525-35843-1 ( Göttinger Universitätsschriften . Volume 13), p. 72 ( limited preview in Google book search and p. 221 limited preview in Google book search)
  8. Hellmuth Vensky: Like a comet Europe panicked. Reported to Zeit Online on May 19, 2010.
  9. a b Georg Brauer , with the collaboration of Marianne Baudler a . a. (Ed.): Handbook of Preparative Inorganic Chemistry . 3rd, revised edition. tape I . Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , pp. 629 .
  10. ^ Henry M. Woodburn et al .: Cynogen . In: Therald Moeller (Ed.): Inorganic Syntheses . tape 5 . McGraw-Hill, Inc., 1957, pp. 43-48 (English).
  11. Hans Schmidt, Hasso Meinert: Electrolyses of cyanides. I. Electrolyses of cyanides in aqueous solutions. In: Journal of Inorganic and General Chemistry. 293, 1957, pp. 214-227, doi : 10.1002 / zaac.19572930309 .
  12. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Structure of Free Molecules in the Gas Phase, pp. 9-34.
  13. John A. Dean: Lange's Handbook of Chemistry . 15th edition. McGraw-Hill, Inc., 1999, ISBN 0-07-016384-7 , pp. 4.43 .
  14. Entry on high temperature chemistry. In: Römpp Online . Georg Thieme Verlag, accessed on July 16, 2014.
  15. ^ E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
  16. a b A. Lieberam: Caloric and critical data. In: Association of German Engineers , VDI Society for Process Engineering and Chemical Engineering (ed.): VDI-Wärmeatlas. Calculation sheets for heat transfer. 7th expanded edition. VDI-Verlag, Düsseldorf 1994, ISBN 3-18-401362-6 , S. Dc1.