Cyanide

Cyanides, salts and other compounds of hydrocyanic acid ( hydrogen cyanide, HCN). In organic chemistry is " cyanide " is outdated, but still quite common name for Nitrile - in the way it regards as esters of hydrogen cyanide - having the general formula R -C ≡ N. The name derives from the Greek κυανός cyanide ( kyanos ), blue ', and touch of the recovery from Eisenhexacyanidoferrat ( Prussian blue ) ago, a pigment with blue color.

Properties

The salt-like cyanides contain the cyanide anion [C ≡ N] -, the organic cyanides the functional group -C ≡ N. Water-soluble cyanides are hydrolyzed in moist air and partly by smell of hydrocyanic acid.

Simple compounds

All cyanides of the alkali and alkaline earth metals are highly toxic and readily soluble in water, such as potassium cyanide ( cyanide ) and sodium cyanide. The toxicity of these salts is due to the release of cyanide from the reaction with the hydrochloric acid of the stomach:

Potassium plays a role in electroplating.

Sodium cyanide is used for gold and silver recovery.

Complex compounds ( cyano compounds )

The cyanide anion is very reactive and forms, with other metals (other than alkali metals and alkaline earth metals ), such as in particular very stable complexes with iron. Usually an anion in which the metal is the central atom of the cyanide components forms. The metal constituting the center and is surrounded by the cyanide ion, such as the [Fe (CN) 6 ] 4 -. It has become a type of connection is formed which is referred to as a complex. Formation of salts with cations such as K 4 [Fe (CN ) 6], Kaliumhexacyanidoferrat (II ), the so-called yellow prussiate of potash. In many complex compounds, the cyanide is tied, goes so that its toxicity (reactivity ) lost. The hydrocyanic acid can be released in part by adding hot dilute sulfuric acid, cyanide complexes should therefore be handled with some caution. Concentrated sulfuric acid does not release hydrogen cyanide, as it hydrolyzes the resulting cyanide immediately to carbon monoxide. Analytically can, however, in aqueous solutions of the complexes no cyanide detected.

Use of the complex compounds in the food industry

In the food industry Cyanido complexes sodium ferrocyanide (E 535 Natriumhexacyanidoferrat (II)), potassium ferrocyanide (E 536, Kaliumhexacyanidoferrat (II)) and Calciumferrocyanid (E 538 Calciumhexacyanidoferrat (II) ) can be used as a food additive. These salts are permitted in small quantities as artificial anti-caking agent, releasing agent and stabilizer for salt and salt substitutes.

Natural Occurrence

Cyanide come - bound in non-toxic cyanogenic glycosides - in the nuclei of many fruits before, such as in Rosaceae ( Prunus species such as plum (Prunus domestica), blackthorn (Prunus spinosa), apricot (Prunus armeniaca ), almond (Prunus dulcis ), Peach ( Prunus persica ), sour cherry (Prunus cerasus) ), in leguminous ( Leguminosae ), spurge such as cassava (Manihot esculenta ), grasses such as sorghum, millets, Leingewächsen, about flax (Linum usitatissimum ), the arum family, Compositae and passion flower plants, but also in ferns how the Goldtüpfelfarn ( Phlebodium aureum ).

Toxic effect

Cyanides such as hydrogen cyanide (HCN ) and the alkali metal salts (e.g., KCN or NaCN ) are highly toxic. Poisoning with these substances may occur as a result of intentional Giftbeibringung at murder and suicide in the industrial and commercial sector as accidents, but also in the private sector. The poison can be added as gaseous hydrogen cyanide via the lungs (eg, by inhalation of fire smoke cyanidhaltigem ), in liquid form (eg biting a cyanide capsule in his mouth ), but also orally as alkali metal salt (eg, either. ingestion of potassium cyanide ).

The mechanism of the cyanide poisoning is due to the inhibition of the enzyme cytochrome c oxidase in the respiratory chain. Thus, the utilization of oxygen is prevented in the cell. Antidotes are 4- dimethylamino phenol hydrochloride (4- DMAP), sodium thiosulfate, hydroxocobalamin (vitamin B12a, in Cyanokit ), amyl nitrite. The binding of cyanide to Fe ( II) ions is relatively low. The inactivation of hemoglobin by binding of Fe (II ) ion, therefore, plays a minor role in poisoning. The bright red color of the skin is a typical sign of poisoning with cyanides: The venous blood is enriched with oxygen, since the oxygen by the cells could not be recycled.

Detoxification process

Most cells contain the enzyme rhodanese, the sulfur binds to the cyanide ion (CN- ), there arises thiocyanate ( SCN- ). This detoxification in the body takes place at a rate of 0.1 mg per kg body weight and hour. Therefore, a longer recording of small amounts of cyanide is harmless, symptoms of poisoning caused by the shock absorption.

Therapy

Usually 4 -DMAP (4- dimethylamino phenol ) or Ethylendiamintetraessigsäurecobalt be administered (II ) complexes as an antidote.

Proof

The high chemical detection of cyanides can be done with Fe3 ions in hydrochloric acid solution after reaction with ammonium polysulfide. Here, the deep red colored Eisenthiocyanat Fe ( SCN ) 3 is formed However, it should be noted that this proof in the presence of Fe ( II), due to the formation of Prussian blue, a complex of Fe ( II) with the Hexacyanidoferrat (III ) as ligands, does not work. But also, the detection with a mixture of iron (II) - and iron ( III) salt are carried out, forming Prussian blue.

Practical Uses

Cyanide solutions are used in practice for extracting precious metals from rocks used ( gold, silver recovery ). Due to the high toxicity of cyanide, this is associated with great potential harm to the environment. Environmental damage can result from the derivation of the sludge or by unsafe deposit. In the Romanian Baia -Mare, it came in 2000 to great environmental damage caused by a dam failure at a gold processing, Turkish Kutahya broke in 2011 two out of three dams a silver preparation.

The European Parliament voted in May 2010 to ban the use of cyanide in mining. Environmental organizations have criticized that cyanide outside the EU will continue to be used in mining, such as in the highlands of the Dominican Republic and Costa Rica.

Disposal

To dispose of cyanides, using a suitable oxidant such as sodium hypochlorite ( NaOCl) or hydrogen peroxide (H2O2). The cyanide is thereby converted into harmless nitrogen and carbon dioxide.

Cyanide may not come into contact with acids in the disposal, otherwise hydrocyanic acid is formed. The conversion for disposal must therefore take place in a basic medium.

Even the autoionization of water ( ) is already sufficient to donate protons for the formation of toxic hydrogen cyanide, so the above alkaline disposal must be observed.