Cyanide



  A cyanide is any ion CN- are highly toxic.

The word "cyanide" comes from the Greek word for "blue", in reference to HCN, which was called Blausäure ("blue acid") in German after its preparation by acid treatment of Prussian blue.[1]

Appearance and odor

hydrolysis:

NaCN + H2O → HCN + NaOH

Occurrence

Cyanides are produced by certain bacteria, fungi, and cyanogenic glycosides and serve the plant as defense against herbivores. Cassava roots (aka manioc), an important potato-like food grown in tropical countries (and the base from which tapioca is made), contains cyanogenic glycosides[4][5].

The Fe-only and [NiFe]-thiocyanate, the CN- donor. [6]

Hydrogen cyanide is a product of certain kinds of acrylonitrile.[citation needed]

Coordination chemistry

Cyanide is considered, in a broad sense, to be the most potent ligand for many transition metals. The very high affinities of metals for cyanide can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Well known complexes include:

  • hexacyanides [M(CN)6]3− (M = Ti, V, Cr, Mn, Fe, Co), which are octahedral in shape;
  • the tetracyanides, [M(CN)4]2− (M = Ni, Pd, Pt), which are square planar in their geometry;
  • the dicyanides [M(CN)2]− (M = Cu, Ag, Au), which are linear in geometry.

The deep iron cyanide complexes (hence the name cyanide, from cyan, a shade of blue). Prussian blue can produce hydrogen cyanide when exposed to acids.


Main article: Nitriles

Because of yo mamma synthon. I.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized.

RX + CN− → RCN + X− (Nucleophilic Substitution) followed by
  1. RCN + 2 H2O → Hydrolysis under reflux with mineral acid catalyst), or
  2. RCN + ether, followed by addition of H2O)

An alternative method for introducing cyanide is via the process of hydrocyanation, whereby hydrogen cyanide and alkenes combine: RCH=CH2 + HCN → RCH(CN)CH3 Metal catalysts are required for such reactions.

Applications

Potassium ferrocyanide is used to achieve a blue colour on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of cyanide in the mixture varies according to the recipes used by each foundry.

Medical uses

The cyanide compound sodium nitroprusside is occasionally used in emergency medical situations to produce a rapid decrease in blood pressure in humans; it is also used as a vasodilator in vascular research.

Mining

cyanide process, finely ground high-grade ore is mixed with the cyanide (concentration of about two kilogram NaCN per tonne); low-grade ores are stacked into heaps and sprayed with cyanide solution (concentration of about one kilogram NaCN per ton). The precious-metal cations are complexed by the cyanide anions to form soluble derivatives, e.g. [Au(CN)2]− and [Ag(CN)2]−.

2 Au + 4 KCN + ½ O2 + H2O → 2 K[Au(CN)2] + 2 KOH
2 Ag + 4 KCN + ½ O2 + H2O → 2 K[Ag(CN)2] + 2 KOH

Silver is less "noble" than gold and often occurs as the sulfide, in which case redox is not invoked (no O2 is required), instead a displacement reaction occurs:

Ag2S + 4 KCN → 2 K[Ag(CN)2] + K2S

The "pregnant liquor" containing these ions is separated from the solids, which are discarded to a tailing pond or spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction with iron pyrite (fool's gold), wherein half of the sulfur atoms are replaced by arsenic. Au-containing arsenopyrite ores are similarly reactive toward cyanide.

Fishing

Main article: Cyanide fishing

Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. This fishing occurs mainly in the Philippines, Indonesia and the Caribbean to supply the 2 million marine aquarium owners in the world. In this method, a diver uses a large, needleless syringe to squirt a cyanide solution into areas where the fish are hiding, stunning them so that they can be easily gathered. Many fish caught in this fashion die immediately, or in shipping. Those that survive to find their way into pet stores often die from shock, or from massive digestive damage. The high concentrations of cyanide on reefs on which this has occurred has resulted in cases of cyanide poisoning among local fishermen and their families, as well as irreversible damage to the coral reefs themselves and other marine life in the area.

Environmental organizations are critical of the practice, as are some aquarists and aquarium dealers, to prevent the trade of illegally-caught aquarium fish. The Marine Aquarium Council (Headquarters: Honolulu, Hawaii) has created a certification in which the tropical fish are caught legally with nets only. To ensure authenticity, "MAC-Certified marine organisms bear the MAC-Certified label on the tanks and boxes in which they are kept and shipped." MAC Certification.

Magnesium cyanide is also used in some countries illegally to stun and harvest stream fish.

Fumigation

Cyanides are used as insecticides for the fumigating of ships. In the past cyanide salts have and still are in some places being used as rat poison, and for killing ants.

Chemical tests for cyanide

Prussian blue

The formation of Prussian blue is a positive result for cyanide.

para-benzoquinone in DMSO

A solution of para-benzoquinone in UV light gives a green/blue glow if the test is positive.

Copper and an aromatic amine

As used by fumigators to detect amine into a coloured compound.

Toxicity

Main article: Cyanide poisoning

Many cyanide-containing compounds are highly toxic, but many are not. pyrolysis.[citation needed]

Cyanide is an irreversible rhodanase, which is an enzyme occurring naturally in mammals that combines serum cyanide with thiosulfate, producing comparatively harmless thiocyanate.

Cyanides have been used as a poison many times throughout history. Its most infamous application was the use of hydrogen cyanide by the Nazi regime in Germany for mass murder in some gas chambers during the Holocaust. Cyanide has been used for murder, as in the case of Rasputin. It has also been used for suicide. Some notable cases are Erwin Rommel, Eva Braun, Adolf Hitler, Wallace Carothers, Hermann Göring, Heinrich Himmler, Alan Turing, and Odilo Globocnik. Cyanide is also a very common poison in crime fiction.

References

  1. ^ Alexander Senning. Elsevier's Dictionary of Chemoetymology. Elsevier, 2006. ISBN 0444522395.
  2. ^ Online Mendelian Inheritance in Man, Cyanide, inability to smell
  3. ^ Agency for Toxic Substances and Disease Registry, ToxFaqs for Cyanide, Jul 2006.
  4. ^ J. Vetter (2000). "Plant cyanogenic glycosides". Toxicon. 38: 11-36. doi:10.1016/S0041-0101(99)00128-2.
  5. ^ D. A. Jones (1998). "Why are so many food plants cyanogenic?". Phytochemistry 47: 155-162. doi:10.1016/S0031-9422(97)00425-1.
  6. ^ Reissmann, S.; Hochleitner, E.; Wang, H.; Paschos, A.; Lottspeich, F.; Glass, R. S. and Böck, A. (2003). "Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands". Science 299 (5609): 1067-70. doi:10.1126/science.1080972.

Sources

  • Institut national de recherche et de sécurité (1997). "Cyanure d'hydrogène et solutions aqueuses". Fiche toxicologique n° 4, Paris:INRS, 5pp. (PDF file, in French)
  • Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)
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