stringtranslate.com

Potassium cyanide

Potassium cyanide is a compound with the formula KCN. It is a colorless salt, similar in appearance to sugar, that is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewellery for chemical gilding and buffing.[4] Potassium cyanide is highly toxic, and a dose of 200 to 300 milligrams will kill nearly any human.

The moist solid emits small amounts of hydrogen cyanide due to hydrolysis (reaction with water). Hydrogen cyanide is often described as having an odor resembling that of bitter almonds.[5][6]

The taste of potassium cyanide has been described as acrid and bitter, with a burning sensation[7][unreliable source?] similar to lye.[8]

Production

KCN is produced by treating hydrogen cyanide with an aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum:[4]

HCN + KOH → KCN + H2O

About 50,000 tons of potassium cyanide are produced yearly.[4] For laboratory purpose it is easier to pass hydrogen cyanide through an alcoholic solution of potassium base because the crystals of potassium cyanide are not soluble in alcohol .

Historical production

Before 1900 and the invention of the Castner process, potassium cyanide was the most important source of alkali metal cyanides.[4] In this historical process, potassium cyanide was produced by decomposing potassium ferrocyanide:[9]

K4[Fe(CN)6] → 4 KCN + FeC2 + N2

Structure

In aqueous solution, KCN is dissociated into hydrated potassium (K+) ions and cyanide (CN−) ions. As a solid, KCN has structure resembling sodium chloride: with each potassium ion surrounded by six cyanide ions, and vice versa. Despite being diatomic, and thus less symmetric than chloride, the cyanide ions rotate so rapidly that their time-averaged shape is spherical. At low temperature and high pressure, this free rotation is hindered, resulting in a less symmetric crystal structure with the cyanide ions arranged in sheets. [10][11]

Applications

KCN and sodium cyanide (NaCN) are widely used in organic synthesis for the preparation of nitriles and carboxylic acids, particularly in the von Richter reaction. It also finds use for the synthesis of hydantoins, which can be useful synthetic intermediates, when reacted with a carbonyl compound such as an aldehyde or ketone in the presence of ammonium carbonate.

KCN is used as a photographic fixer in the wet plate collodion process.[12] The KCN dissolves silver where it has not been made insoluble by the developer. This reveals and stabilizes the image, making it no longer sensitive to light. Modern wet plate photographers may prefer less toxic fixers, often opting for sodium thiosulfate, but KCN is still used.

In the 19th century, cyanogen soap, a preparation containing potassium cyanide, was used by photographers to remove silver stains from their hands.[13]: 11 [14]: 73 [15]

Potassium gold cyanide

In gold mining, KCN forms the water-soluble salt potassium gold cyanide (or gold potassium cyanide) and potassium hydroxide from gold metal in the presence of oxygen (usually from the surrounding air) and water:

4 Au + 8 KCN + O2 + 2 H2O → 4 K[Au(CN)2] + 4 KOH

A similar process uses NaCN to produce sodium gold cyanide (NaAu(CN2)).

Toxicity

Potassium cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase, hence blocking oxidative phosphorylation. Lactic acidosis then occurs as a consequence of anaerobic metabolism. Initially, acute cyanide poisoning causes a red or ruddy complexion in the victim because the tissues are not able to use the oxygen in the blood. The effects of potassium cyanide and sodium cyanide are identical, and symptoms of poisoning typically occur within a few minutes of ingesting the substance: the person loses consciousness, and brain death eventually follows. During this period the victim may suffer convulsions. Death is caused by histotoxic hypoxia/cerebral hypoxia. The expected LD100 dose (human) for potassium cyanide is 200–300 mg while the median lethal dose LD50 is estimated at 140 mg.[16]

People who died by suicide, were killed, or killed someone else using potassium cyanide include:

It is used by professional entomologists as a killing agent in collecting jars, as insects succumb within seconds to the HCN fumes it emits, thereby minimizing damage to even highly fragile specimens.

KCN can be detoxified most efficiently with hydrogen peroxide or with a solution of sodium hypochlorite (NaOCl). Such solutions should be kept alkaline whenever possible so as to eliminate the possibility of generation of hydrogen cyanide:[4]

KCN + H2O2 → KOCN + H2O
KCN + NaOCl → KOCN + NaCl


References

  1. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0522". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ "Cyanides (as CN)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. ^ "Potassium Cyanide | Cameo Chemicals | NOAA".
  4. ^ a b c d e Andreas Rubo, Raf Kellens, Jay Reddy, Joshua Wooten, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Industrial Chemistry 2006 Wiley-VCH, Weinheim, Germany. doi:10.1002/14356007.i01_i01
  5. ^ "Suicide note reveals taste of cyanide". 8 July 2006.
  6. ^ Not everyone, however, can smell cyanide; the ability to do so is a genetic trait.Online Mendelian Inheritance in Man (OMIM): 304300
  7. ^ ലേഖകൻ, മാധ്യമം (19 December 2021). "'സയനൈഡ് ചവർപ്പാണ്... പുകച്ചിലാണ്...'; ആ 'രുചി രഹസ്യം' പുറത്തുവിട്ട മലയാളി നടന്ന വഴിയിലൂടെ | Madhyamam". www.madhyamam.com (in Malayalam). Retrieved 21 December 2021.
  8. ^ "The only taste: Cyanide is acrid". hindustantimes.com. Hindustan Times. 8 July 2006.
  9. ^ Von Wagner, Rudolf (1897). Manual of chemical technology. New York: D. Appleton & Co. pp. 474 & 477.
  10. ^ Crystallography Open Database, Structure of KCN
  11. ^ H. T. Stokes; D. L. Decker; H. M. Nelson; J. D. Jorgensen (1993). "Structure of potassium cyanide at low temperature and high pressure determined by neutron diffraction". Physical Review B (Submitted manuscript). 47 (17): 11082–11092. Bibcode:1993PhRvB..4711082S. doi:10.1103/PhysRevB.47.11082. PMID 10005242..
  12. ^ J. Towler, MD. "The Silver Sunbeam (Facsimile 1864 edition, 1969)" p. 119
  13. ^ Crookes, William, ed. (10 September 1858). "Photographic Notes and Queries". The Photographic News: A Weekly Record of the Progress of Photography. 1 (1). London: Cassell, Petter, and Galpin: 10–12.
  14. ^ Reports of Trials for Murder by Poisoning; by Prussic Acid, Strychnia, Antimony, Arsenic, and Aconita. Including the trials of Tawell, W. Palmer, Dove, Madeline Smith, Dr. Pritchard, Smethurst, and Dr. Lamson, with chemical introduction and notes on the poisons used, G. Lathom Browne and C. G. Stewart, London: Stevens and Sons, 1883; redistributed by Project Gutenberg.
  15. ^ "Cyanuret of potassium", Paper, Shadows and Light, Robert Douglas. Accessed 2024-01-20.
  16. ^ John Harris Trestrail III. Criminal Poisoning –Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists, and Attorneys (2nd ed.) p. 119
  17. ^ "Top 10 Scientists who Committed Suicide". 7 October 2007.
  18. ^ "War criminal 'took cyanide' in Hague court". BBC News. 1 December 2017. Retrieved 1 December 2017.

External links