Potassium cyanide
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| Names | |
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| IUPAC name
Potassium cyanide
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| Identifiers | |
3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.005.267 |
| EC Number |
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PubChemCID
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| RTECS number |
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| UNII | |
| UN number | 1680 |
CompTox Dashboard(EPA)
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| Properties | |
| KCN | |
| Molar mass | 65.12 g/mol |
| Appearance | White crystalline solid deliquescent |
| Odor | faint,bitter almond-like |
| Density | 1.52 g/cm3 |
| Melting point | 634.5 °C (1,174.1 °F; 907.6 K) |
| Boiling point | 1,625 °C (2,957 °F; 1,898 K) |
| 71.6 g/100 ml (25 °C) 100 g/100 ml (100 °C) | |
| Solubilityinmethanol | 4.91 g/100 ml (20 °C) |
| Solubilityinglycerol | soluble |
| Solubilityinformamide | 14.6 g/100 mL |
| Solubilityinethanol | 0.57 g/100ml |
| Solubilityinhydroxylamine | 41 g/100 ml |
| Acidity(pKa) | 11.0 |
| −37.0·10−6cm3/mol | |
Refractive index(nD)
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1.410 |
| Thermochemistry | |
Std molar
entropy(S⦵298) |
127.8 J K−1 mol−1 |
Std enthalpy of
formation(ΔfH⦵298) |
−131.5 kJ/mol |
| Hazards | |
| GHSlabelling: | |
   
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| Danger | |
| H290,H300,H310,H330,H370,H372,H410 | |
| P260,P264,P273,P280,P284,P301+P310 | |
| NFPA 704(fire diamond) | |
| Flash point | Non-flammable |
| Lethal doseor concentration (LD, LC): | |
LD50(median dose)
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5 mg/kg (oral, rabbit) 10 mg/kg (oral, rat) 5 mg/kg (oral, rat) 8.5 mg/kg (oral, mouse)[2] |
| NIOSH(US health exposure limits): | |
PEL(Permissible)
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TWA 5 mg/m3[1] |
REL(Recommended)
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C 5 mg/m3(4.7 ppm) [10-minute][1] |
IDLH(Immediate danger)
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25 mg/m3[1] |
| Safety data sheet(SDS) | ICSC 0671 |
| Related compounds | |
Otheranions
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Potassium cyanate Potassium thiocyanate |
Othercations
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Sodium cyanide Rubidium cyanide lithium cyanide caesium cyanide |
Related compounds
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Hydrogen cyanide |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Potassium cyanideis a compound with theformulaKCN.It is a colorless salt, similar in appearance tosugar,that is highlysolublein water. Most KCN is used ingold mining,organic synthesis,andelectroplating.Smaller applications includejewelleryfor chemicalgildingandbuffing.[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 ofhydrogen cyanidedue tohydrolysis(reaction with water). Hydrogen cyanide is often described as having an odor resembling that ofbitter 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
[edit]KCN is produced by treatinghydrogen cyanidewith an aqueous solution ofpotassium hydroxide,followed by evaporation of the solution in a vacuum:[4]
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
[edit]Before 1900 and the invention of theCastner process,potassium cyanide was the most important source ofalkali metalcyanides.[4]In this historical process, potassium cyanide was produced by decomposingpotassium ferrocyanide:[9]
Structure
[edit]In aqueous solution, KCN is dissociated into hydrated potassium (K+) ions andcyanide(CN−) ions. As a solid, KCN has structure resemblingsodium 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
[edit]KCN andsodium cyanide(NaCN) are widely used inorganic synthesisfor the preparation ofnitrilesandcarboxylic acids,particularly in thevon Richter reaction.It also finds use for the synthesis ofhydantoins,which can be useful synthetic intermediates, when reacted with a carbonyl compound such as analdehydeorketonein the presence ofammonium carbonate.
KCN is used as aphotographic fixerin the wet platecollodion 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 forsodium thiosulfate,but KCN is still used.
In the 19th century, cyanogensoap,a preparation containing potassium cyanide, was used byphotographersto removesilverstains from their hands.[13]: 11 [14]: 73 [15]
Potassium gold cyanide
[edit]Ingold mining,KCN forms the water-soluble saltpotassium 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 producesodium gold cyanide(NaAu(CN2)).
Toxicity
[edit]Potassium cyanide is a potent inhibitor ofcellular respiration,acting on mitochondrialcytochrome c oxidase,hence blockingoxidative phosphorylation.Lactic acidosisthen occurs as a consequence ofanaerobic metabolism.Initially, acute cyanide poisoning causes a red or ruddy complexion in the victim because the tissues are not able to use theoxygenin 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, andbrain deatheventually follows. During this period the victim may sufferconvulsions.Death is caused bycerebral 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 bysuicide,were killed, or killed someone else using potassium cyanide include:
- Viktor Meyer,19th-century German chemist, died by suicide in 1897 after taking cyanide[17]
- Gustav Wied,Danish novelist, poet, and playwright, in 1914
- Pritilata Waddedar,an Indian revolutionary nationalist, took cyanide in 1932 to avoid capture byIndian Imperial Police,British India
- Badal Gupta,a revolutionary from Bengal, who launched an attack on the Writers' Building in Kolkata, consumed cyanide in 1930 immediately after the attack.
- Wallace Carothers,polymer chemist who died by suicide in 1937 after battling depression for years
- Senior figures inNazi Germany,such asErwin Rommel,Hitler's longtime companionEva Braun,Joseph Goebbels,Heinrich Himmler,andHermann Göring
- Alan Turing,a computer scientist who died of cyanide poisoning in 1954
- Ronald Clark O'Bryan,a Texas optician who killed his son by lacing apixy stickwith potassium cyanide in 1974
- Peoples Temple,the 1978cult suicidein (Jonestown), Guyana
- Members of theLTTEinvolved in the assassination of Indian prime ministerRajiv Gandhiin 1991
- Ramon Sampedro,Spanish tetraplegic and activist whose assisted suicide in 1998 provoked a national debate about euthanasia, and was the subject of the Oscar-winning film "The Sea Inside"
- Jason Altom,a promising graduate student in the lab of Nobel Prize–winning chemistEJ Coreyat Harvard, died after drinking potassium cyanide in 1998
- Slobodan Praljak,a wartime general in Republic of Croatia, died by suicide by drinking from a vial containing potassium cyanide during the reading of his appeal judgment inThe HagueonInternational Criminal Tribunal for the former Yugoslavia(ICTY) on 29 November 2017.[18]
It is used by professionalentomologistsas a killing agent incollecting jars,asinsectssuccumb within seconds to the HCN fumes it emits, thereby minimizing damage to even highly fragile specimens.
KCN can be detoxified most efficiently withhydrogen peroxideor with a solution ofsodium hypochlorite(NaOCl). Such solutions should be kept alkaline whenever possible so as to eliminate the possibility of generation of hydrogen cyanide:[4]
References
[edit]- ^abcNIOSH Pocket Guide to Chemical Hazards."#0522".National Institute for Occupational Safety and Health(NIOSH).
- ^"Cyanides (as CN)".Immediately Dangerous to Life or Health Concentrations (IDLH).National Institute for Occupational Safety and Health(NIOSH).
- ^"POTASSIUM CYANIDE | CAMEO Chemicals | NOAA".
- ^abcdeAndreas 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
- ^"Suicide note reveals taste of cyanide".8 July 2006.
- ^Not everyone, however, can smell cyanide; the ability to do so is agenetic trait.Online Mendelian Inheritance in Man(OMIM):304300
- ^ലേഖകൻ, മാധ്യമം (19 December 2021)."'സയനൈഡ് ചവർപ്പാണ്... പുകച്ചിലാണ്...'; ആ 'രുചി രഹസ്യം' പുറത്തുവിട്ട മലയാളി നടന്ന വഴിയിലൂടെ | Madhyamam ".www.madhyamam.com(in Malayalam).Retrieved21 December2021.
- ^"The only taste: Cyanide is acrid".hindustantimes.com.Hindustan Times. 8 July 2006.
- ^Von Wagner, Rudolf (1897).Manual of chemical technology.New York: D. Appleton & Co. p. 474 & 477.
- ^Crystallography Open Database, Structure of KCN
- ^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.PMID10005242..
- ^J. Towler, MD. "The Silver Sunbeam (Facsimile 1864 edition, 1969)" pg 119
- ^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.
- ^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 byProject Gutenberg.
- ^"Cyanuret of potassium",Paper, Shadows and Light, Robert Douglas. Accessed 2024-01-20.
- ^John Harris Trestrail III.Criminal Poisoning - Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists, and Attorneys (2nd edition).p. 119
- ^"Top 10 Scientists who Committed Suicide".7 October 2007.
- ^"War criminal 'took cyanide' in Hague court".BBC News.1 December 2017.Retrieved1 December2017.
External links
[edit]- International Chemical Safety Card 0671
- Hydrogen cyanide and cyanides(CICAD61)
- National Pollutant Inventory - Cyanide compounds fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- CSST (Canada)
- NIST Standard Reference Database
- Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium".Fiche toxicologique n° 111,Paris:INRS, 6pp.(in French)
