Cyanogen halide
| X-C≡N |
A cyanogen halide is a molecule consisting of cyanide and a halogen. Cyanogen halides are chemically classified as pseudohalogens.
The cyanogen halides are a group of chemically reactive compounds which contain a cyano group (-CN) attached to a halogen element, such as fluorine, chlorine, bromine or iodine. Cyanogen halides are colorless, volatile, lacrimatory (tear-producing) and highly poisonous compounds.
Production
[edit]Halogen cyanides can be obtained by the reaction of halogens with metal cyanides or the halogenation of hydrocyanic acid.[1][2]
- M = metal, X = halogen
Cyanogen fluoride can be obtained by thermal decomposition of cyanuric fluoride.
Properties
[edit]Halogen cyanides are stable at normal pressure below 20 °C and in the absence of moisture or acids. In the presence of free halogens or Lewis acids[3] they easily polymerize to cyanuric halides, for example cyanogen chloride to cyanuric chloride. They are very toxic and tear-inducing (lachrymatory). Cyanogen chloride melts at −6 °C and boils at about 150 °C. Bromine cyanide melts at 52 °C and boils at 61 °C. Iodine cyanide sublimates at normal pressure.[1] Cyanogen fluoride boils at −46 °C and polymerizes at room temperature to cyanuric fluoride.[4]
In some of their reactions they resemble halogens.[2][3] The hydrolysis of cyanogen halides takes place in different ways depending on the electronegativity of the halogen and the resulting different polarity of the X-C bond.[5]
| (X = F, Cl) | ||
| (X = Br, I) |
Cyanogen fluoride is a gas produced by heating cyanuric fluoride. Cyanogen chloride is a liquid produced by reacting chlorine with hydrocyanic acid.
Biomedical effects and metabolism of cyanogen halides
[edit]Cyanide is naturally present in human tissues in very small quantities. It is metabolized by rhodanese, a live enzyme at a rate of approximately 17 μg/kg·min. Rhodanese catalyzes the irreversible reaction forming thiocyanate from cyanide and sulfane which is non-toxic and can be excreted through the urine. Under normal conditions, availability of sulfane is the limiting factor which acts as a substrate for rhodanese. Sulfur can be administered therapeutically as sodium thiosulfate to accelerate the reaction. A lethal dose of cyanide is time-dependent because of the body's ability to detoxify and excrete small amounts of cyanide through rhodanese-sulfate catalysis. If an amount of cyanide is absorbed slowly, rhodanese-sulfate may be able to biologically render it non-toxic through catalysis to thiosulfate whereas the same amount administered over a short period of time may be lethal.[6]
Use
[edit]Halogen cyanides, in particular cyanogen chloride and cyanogen bromide, are important starting materials for the incorporation of the cyanogen group, the production of other carbonic acid derivatives and heterocycles.[3]
It has been suggested that cyanogen chloride be used by the military as poison gas. Cyanogen bromide is a solid that is prepared by reacting bromine with hydrocyanic acid salts; it has been used as a chemical pesticide against insects and rodents and as a reagent for the study of protein structure.[7] Cyanogen halides have been found to act as electrolytes in liquid solvents, sulfur dioxide, arsenous chloride, and sulfuryl chloride.
See also
[edit]References
[edit]- ^ a b C.R. Noller (2013), Lehrbuch der Organischen Chemie (in German), Springer-Verlag, p. 335, ISBN 978-3-642-87324-9
- ^ a b Houben-Weyl Methods of Organic Chemistry Vol. VIII, 4th Edition Peroxides, Carbonic Acid Derivatives, Carboxylic Acids, Carboxylic Acid Derivatives (in German), Georg Thieme Verlag, 2014, p. 90, ISBN 978-3-13-180534-8
- ^ a b c Houben-Weyl Methods of Organic Chemistry Vol. E 4, 4th Edition Supplement Carbonic Acid Derivatives (in German), Georg Thieme Verlag, 2014, p. 915, ISBN 978-3-13-181144-8
- ^ Georg Brauer (Hrsg.), unter Mitarbeit von Marianne Baudler u. a.: Handbuch der Präparativen Anorganischen Chemie. 3., umgearbeitete Auflage. Band I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6, S. 227.
- ^ spektrum.de: Halogencyane - Lexikon der Chemie - Spektrum der Wissenschaft, retrieved 22 January 2017.
- ^ "Iodine cyanide". PubChem. NIH. Retrieved 2012-04-27.
- ^ "Cyanogen halide". Encyclopædia Britannica. 2012. Retrieved 2012-04-27.