Szerkesztő:Dorgan/Hidrogén-cianid

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Hydrogen cyanide

Hydrogen cyanide bonding
Hydrogen cyanide space filling
IUPAC-név formonitrile
Más nevek hydrogen cyanide; methanenitrile; hydrocyanic acid; prussic acid; Zyklon B
Kémiai azonosítók
CAS-szám 74-90-8
PubChem 768
EINECS-szám 200-821-6
RTECS szám MW6825000
SMILES
C#N
Kémiai és fizikai tulajdonságok
Kémiai képlet HCN
Moláris tömeg 27.0253 g/mol
Megjelenés Colorless gas or pale blue
highly volatile liquid
Sűrűség 0.687 g/cm3, liquid.
Olvadáspont −13,4 °C
Forráspont 25,6 °C
Oldhatóság (vízben) completely miscible
Savasság (pKa) 9.21
Törésmutató (nD) 1.2675 [1]
Viszkozitás 0.201 cP
Kristályszerkezet
Molekulaforma Linear
Dipólusmomentum 2.98 D
Termokémia
Std. képződési
entalpia ΔfHo298		 -4.999 kJ/g
Égés standard-
entalpiája ΔcHo298		 -24.6 kJ/g
Hőkapacitás, C 1.328 J/(g·K) (gas)
2.612 J/(g·K) (liquid)
Veszélyek
EU osztályozás Extremely flammable (F+)
Very toxic (T+)
Dangerous for the environment (N)
EU Index 006-006-00-X
NFPA 704
4
4
1
 
R mondatok R12, R26, R50/53
S mondatok (S1/2), S7/9, S16, S36/37, S38, S45, S60, S61
Lobbanáspont −17.8 °C (−64 °F)
Öngyulladási hőmérséklet 538 °C
Rokon vegyületek
Rokon vegyületek Cyanogen
Cyanogen chloride
Trimethylsilyl cyanide
Methylidynephosphane
Ha másként nem jelöljük, az adatok az anyag standardállapotára (100 kPa) és 25 °C-os hőmérsékletre vonatkoznak.

A hidrogén-cianid (HCN, régebbi nevén kéksav) keserűmandula szagú, könnyen párolgó, rendkívül mérgező, színtelen folyadék, forráspontja 26 °C. Molekulái lineáris felépítésűek, a szénatom a nitrogénatomhoz háromszoros kovalens kötéssel kapcsolódik. Legfőbb tautomerje a HNC (hidrogén-izocianid).

Nagyon gyenge sav, ennek ellenére molekulái erősen polárisak. Vízzel minden arányban elegyedik, vízmentes állapotban meggyújtható, szén-dioxiddá, vízzé és szabad nitrogénné ég el. Sói a cianidok.

HCN has a faint, bitter, burnt almond-like odor that some people are unable to detect due to a genetic trait.[2] The volatile compound has been used as inhalation rodenticide and human poison. Cyanide ions interfere with iron-containing respiratory enzymes.

HCN is produced on an industrial scale, and is a highly valuable precursor to many chemical compounds, ranging from polymers to pharmaceuticals.

History of discovery[szerkesztés]

A hidrogén-cianidot először a Berlini-kék nevű pigmentből állítottak elő, melyet már 1704 óta ismertek. A szerkezete azonban ismeretlen volt. A pigmentet jelenleg koordinációs polimerként tartják számon komplex struktúrával, mely hidratált ferri-ferrocianid. 1752-ben egy francia kémikus Pierre Macquer kísérletete világított rá arra, hogy a Berlini-kék vas-oxiddá és egy könnyen párolgó vegyületté alakítható, melyekből a festéket újból elő lehet állítani. A párolgó vegyület, melyet előállított a hidrogén-cianid volt. Following Macquer's lead, it was first isolated from Prussian blue in pure form and characterized about 1783 by the Swedish chemist Carl Wilhelm Scheele, and was eventually given the German name Blausäure (literally "Blue acid") because of its acidic nature in water and its derivation from Prussian blue. In English it became known popularly as Prussic acid.

Anion of Prussian blue

In 1787 the French chemist Claude Louis Berthollet showed that Prussic acid did not contain oxygen, an important contribution to acid theory, which had hitherto postulated that acids must contain oxygen[3] (hence the name of oxygen itself, which is derived from Greek elements that mean "acid-former" and are likewise calqued into German as Sauerstoff). In 1815 Joseph Louis Gay-Lussac deduced Prussic acid's chemical formula. The radical cyanide in hydrogen cyanide was given its name from the Greek word for blue, again due to its derivation from Prussian blue.

Production and synthesis[szerkesztés]

Iparilag Andruszov módszerével nyerik metán, ammónia és levegő elegyéből, platina katalizátor jelenlétében, 1200 °C körüli hőmérsékleten. A reakcióhoz szükséges energiát a metán és az ammónia egy részének oxidálásával nyerik.


Of lesser importance is the Degussa process (BMA process) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall:[4]

CH4 + NH3 → HCN + 3H2

This reaction is akin to steam reforming, the reaction of methane and water to give carbon monoxide and hydrogen.

In the Shawinigan Process, ammonia and natural gas are passed over coke. As practiced at BASF, formamide is heated and split into hydrogen cyanide and water:

CH(O)NH2 → HCN + H2O

Laboratóriumban a hidrogén-cianidot alkálifém-sóinak savas kezelése útján állítják elő:

H+ + NaCN → HCN + Na+

This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.

Historical methods of production[szerkesztés]

The demand for cyanides for mining operations in the 1890s was met by George Thomas Beilby, who patented a method to produce hydrogen cyanide by passing ammonia over glowing coal in 1892. This method was used until Hamilton Castner in 1894 developed a synthesis starting from coal, ammonia, and sodium yielding sodium cyanide, which reacts with acid to form gaseous HCN.

Applications[szerkesztés]

A hidrogén-cianidból nátrium-cianidot és kálium-cianidot állítanak elő, mely vegyületeket régebben rágcsálók írtására használták, napjainkban leginkább a bányászat használja fel őket. Via the intermediacy of cyanohydrins, a variety of useful organic compounds are prepared from HCN including the monomer methyl methacrylate, from acetone, the amino acid methionine, via the Strecker synthesis, and the chelating agents EDTA and NTA. Via the hydrocyanation process, HCN is added to butadiene to give adiponitrile, a precursor to Nylon 66.[5]

Occurrence[szerkesztés]

HCN is obtainable from fruits that have a pit, such as cherries, apricots, apples, and bitter almonds, from which almond oil and flavoring are made. Many of these pits contain small amounts of cyanohydrins such as mandelonitrile and amygdalin, which slowly release hydrogen cyanide.[6][7] One hundred grams of crushed apple seeds can yield about 10 mg of HCN.[forrás?] Some millipedes release hydrogen cyanide as a defense mechanism,[8] as do certain insects such as some burnet moths. Hydrogen cyanide is contained in the exhaust of vehicles, in tobacco and wood smoke, and in smoke from burning nitrogen-containing plastics. So-called "bitter" roots of the cassava plant may contain up to 1 gram of HCN per kilogram.[9][10]

HCN and the origin of life[szerkesztés]

Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids. It is possible, for example, that HCN played a part in the origin of life.[11] Although the relationship of these chemical reactions to the origin of life remains speculative, studies in this area have led to discoveries of new pathways to organic compounds derived from condensation of HCN.[12]

HCN in space[szerkesztés]

Lásd még: Astrochemistry

HCN has been detected in the interstellar medium.[13] Since then, extensive studies have probed formation and destruction pathways of HCN in various environments and examined its use as a tracer for a variety of astronomical species and processes. HCN can be observed from ground-based telescopes through a number of atmospheric windows.[forrás?] The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.[13][14][15]

HCN is formed in interstellar clouds through one of two major pathways:[16] via a neutral-neutral reaction (CH2 + N → HCN + H) and via dissociative recombination (HCNH+ + e- → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the HCNH+ must be in its linear form. Dissociative recombination with its structural isomer, H2NC+ produces hydrogen isocyanide (HNC), exclusively.

HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud.[16] In photon-dominated regions (PDRs), photodissociation dominates, producing CN (HCN + ν → CN + H). At further depths, photodissociation by cosmic rays dominate, producing CN (HCN + cr → CN + H). In the dark core, two competing mechanisms destroy it, forming HCN+ and HCNH+ (HCN + H+ → HCN+ + H; HCN + HCO+ → HCNH+ + CO). The reaction with HCO+ dominates by a factor of ~3.5. HCN has been used to analyze a variety of species and processes in the interstellar medium. It has been suggested as a tracer for dense molecular gas[17][18] and as a tracer of stellar inflow in high-mass star-forming regions[19]. Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs).[20]

A hidrogén-cianid mint méreg és mint kémiai fegyver[szerkesztés]

300 mg/m3-es hidrogén-cianid koncentráció a levegőben 10 perc alatt halált okoz. 3200 mg/m3-es koncentráció már 1 percen belül öl. The toxicity is caused by the cyanide ion, which halts cellular respiration by inhibiting an enzyme in mitochondria called cytochrome c oxidase.

Hydrogen cyanide absorbed into a carrier for use as a pesticide (under IG Farben's brand name Cyclone B, or in German Zyklon B, with the B standing for Blausäure)[21] was most infamously employed by Nazi Germany in the mid-20th century in extermination camps. The same product is currently made in the Czech Republic under the trademark "Uragan D2." Hydrogen cyanide is also the agent used in gas chambers employed in judicial execution in some U.S. states, where it is produced during the execution by the action of sulfuric acid on an egg-sized mass of potassium cyanide.

Hydrogen cyanide is commonly listed amongst chemical warfare agents that cause general poisoning and skin blisters.[22] As a substance listed under Schedule 3 of the Chemical Weapons Convention as a potential weapon which has large-scale industrial uses, manufacturing plants in signatory countries which produce more than 30 tonnes per year must be declared to, and can be inspected by, the Organisation for the Prohibition of Chemical Weapons.

Under the name prussic acid, HCN has been used as a killing agent in whaling harpoons.[23]

Hydrogen cyanide gas in air is explosive at concentrations over 5.6%, equivalent to 56000 ppm[24].

External links[szerkesztés]

References[szerkesztés]

  1. ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
  2. ↑ Cyanide, inability to smell. Online Mendelian Inheritance in Man. (Hozzáférés: 2010. március 31.)
  3. ↑ Brian T Newbold: Claude Louis Berthollet: A Great Chemist in +he french Tradition.. Canadian Chemical News, 1999. november 1. (Hozzáférés: 2010. március 31.)
  4. ↑ F. Endter (1958). „Die technische Synthese von Cyanwasserstoff aus Methan und Ammoniak ohne Zusatz von Sauerstoff”. Chemie Ingenieur Technik 30 (5), 281–376. o. DOI:10.1002/cite.330300506.  
  5. ↑ Forráshivatkozás-hiba: Érvénytelen <ref> címke; nincs megadva szöveg a(z) Ullmmann nevű lábjegyzeteknek
  6. ↑ J. Vetter (2000). „Plant cyanogenic glycosides”. Toxicon 38 (1), 11–36. o. DOI:10.1016/S0041-0101(99)00128-2. PMID 10669009.  
  7. ↑ D. A. Jones (1998). „Why are so many food plants cyanogenic?”. Phytochemistry 47, 155–162. o. DOI:10.1016/S0031-9422(97)00425-1.  
  8. ↑ M. S. Blum, J. P. Woodring (1962). „Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede Pachydesmus crassicutis (Wood)”. Science 138 (3539), 512–513. o. DOI:10.1126/science.138.3539.512. PMID 17753947.  
  9. ↑ Aregheore E. M, Agunbiade O. O. (1991). „The toxic effects of cassava (manihot esculenta grantz) diets on humans: a review.”. Vet. Hum. Toxicol. 33 (3), 274–275. o. PMID 1650055.  
  10. ↑ White W. L. B., Arias-Garzon D. I., McMahon J. M., Sayre R. T. (1998). „Cyanogenesis in Cassava, The Role of Hydroxynitrile Lyase in Root Cyanide Production”. Plant Physiology 116 (4), 1219–1225. o. DOI:10.1104/pp.116.4.1219. PMID 9536038.  
  11. ↑ Matthews, C. N. "The HCN World: Establishing Protein-Nucleic Augucid Life via Hydrogen Cyanide Polymers" Cellular Origin and Life in Extreme Habitats and Astrobiology (2004), 6 (Origins : Genesis, Evoluation and Diversity of Life), 121-135.
  12. ↑ Al-Azmi, A.; Elassar, A.-Z. A.; Booth, B. L. "The Chemistry of Diaminomaleonitrile and its Utility in Heterocyclic Synthesis" Tetrahedron (2003), 59, 2749-2763. CODEN: TETRAB ISSN:0040-4020
  13. ↑ a b Snyder, Lewis E.; Buhl, David (1971). „Observations of Radio Emission from Interstellar Hydrogen Cyanide”. Astrophysical Journal 163, L47. o. DOI:10.1086/180664.  
  14. ↑ Bieging, J. H. et al. (2000). „Submillimeter‐ and Millimeter‐Wavelength Observations of SiO and HCN in Circumstellar Envelopes of AGB Stars”. Astrophysical Journal 543, 897. o. DOI:10.1086/317129.  
  15. ↑ Schilke, P. and Menten, K. M. (2003). „Detection of a Second, Strong Sub-millimeter HCN Laser Line toward Carbon Stars”. Astrophysical Journal 583, 446. o. DOI:10.1086/345099.  
  16. ↑ a b Boger, G. I. and Sternberg, A. (2005). „CN and HCN in Dense Interstellar Clouds”. Astrophysical Journal 632, 302. o. DOI:10.1086/432864.  
  17. ↑ Gao, Y. and Solomon, P. M. (2004). „The Star Formation Rate and Dense Molecular Gas in Galaxies”. Astrophysical Journal 606, 271. o. DOI:10.1086/382999.  
  18. ↑ Gao, Y. and Solomon, P. M. (2004). „HCN Survey of Normal Spiral, Infrared‐luminous, and Ultraluminous Galaxies”. Astrophysical Journal Supplements 152, 63. o. DOI:10.1086/383003.  
  19. ↑ Wu, J. and Evans, N. J. (2003). „Indications of Inflow Motions in Regions Forming Massive Stars”. Astrophysical Journal 592, L79. o. DOI:10.1086/377679.  
  20. ↑ Loenen, A. F. et al. (2007). „”. Proceedings IAU Symposium 202.  
  21. ↑ Dwork, Deborah, van Pelt, Robert Jan. Auschwitz, 1270 to the present. Norton, 219. o. (1996). ISBN 0393039331 
  22. ↑ Hydrogen Cyanide. Organisation for the Prohibition of Chemical Weapons. (Hozzáférés: 2009. január 14.)
  23. ↑ Poison Hand Darted Harpoons and Lances
  24. ↑ Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs) - 74908
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