Cyanide specifically refers to a compound with a cyano group (CN), in which the carbon atom and the nitrogen atom are connected by a triple bond. This triple bond gives the cyano group a very high stability, so that it exists as a whole in the usual chemical reactions. Because this group has similar chemical properties to halogen, it is often called pseudo-halogen. Cyanides generally known to people are inorganic cyanides, which refer to inorganic salts containing cyanide ions (CN-), which can be considered as salts of hydrocyanic acid (HCN). Common ones are potassium cyanide and sodium cyanide . They are highly toxic. There are also organic cyanides, which are formed by combining a cyano group with another carbon atom through a single bond. Depending on the binding mode, organic cyanides can be classified into nitrile (C-CN) and isonitrile (C-NC). Correspondingly, cyano groups can be called nitrile (-CN) or isonitrile (-NC). . Cyanide can be divided into inorganic cyanide, such as hydrocyanic acid, potassium (sodium) cyanide, cyanogen chloride, etc.; organic cyanide, such as acetonitrile, acrylonitrile, n-butyronitrile, etc. can quickly precipitate ions in the body. It is highly toxic. Many cyanides, which can release hydrogen cyanide or cyanide ions after heating or reacting with acid, or in the air and tissues, have the same highly toxic effects as hydrogen cyanide.
Cyanide is widely used in industry. For example, people engaged in electroplating, washing and injection, paint, dyes, rubber and other industries have more exposure opportunities. In daily life, peaches, plums, apricots, and loquats contain hydrocyanic acid, of which bitter almonds have the highest content, and cassava also contains hydrocyanic acid.
Occupational cyanide poisoning is mainly through the respiratory tract, and secondly, it can be absorbed through the skin at high concentrations.
Living cyanide poisoning is mainly oral. The oral mucosa and digestive tract can be fully absorbed.
Cyanide enters the human body and releases cyanide ions, which combine with the ferric iron of the oxidative cytochrome oxidase in the cell mitochondria to prevent the ferric iron in the oxidase from reducing and hinder the normal respiration of the cells. The tissue cells cannot use oxygen, resulting in hypoxia. , Causing the body to fall into a state of suffocation. In addition, the molecules of certain nitrile compounds have a direct inhibitory effect on the central nervous system.
Cyanide is a very useful reagent in organic synthesis. It is often used to introduce a cyano group into the molecule to generate organic cyanide, that is, nitrile. For example, acrylic fiber commonly used in textiles, its chemical name is polyacrylonitrile. Nitriles can generate carboxylic acids by hydrolysis; amines can be generated by reduction, and so on. Many other functional groups can be derived. It is also used in the condensation of benzoin. The aromatic aldehyde undergoes bimolecular condensation reaction in the alcohol-water solution under the action of potassium cyanide (highly toxic) to generate α-hydroxyketone. In addition to aromatic aldehydes, certain fatty aldehydes that do not contain α-hydrogen can also react in the same way.
Existence and application
Cyanide has a daunting toxicity, but they are by no means a chemist's creation, on the contrary, they are widespread in nature, especially in the biological world. Cyanide can be produced by certain bacteria, fungi or algae, and is found in many foods and plants. In plants, cyanide is usually combined with sugar molecules and exists in the form of cyanogenic glycoside. For example, cassava contains cyanogenic glycosides, which must be removed before consumption (usually by continuous boiling). Fruit cores usually contain cyanide or cyanogenic glycosides. For example, the amygdalin contained in almonds is a kind of cyanogenic glycoside, so it is usually soaked in warm water to detoxify before eating almonds.
Human activities also lead to the formation of cyanide. Both car exhaust and cigarette smoke contain hydrogen cyanide, and burning certain plastics and wool can also produce hydrogen cyanide.
While discovering that HCN also exists in space, according to S Miller's experiment, it is pointed out that it is an intermediate product in the generation of amino acids from methane, ammonia, and water through electric discharge. Therefore, it is considered to be an important intermediate product in the production of organic matter in the past. In fact, adenine is produced by heating with ammonia and aqueous solution. Although HCN does not exist much in the body, it can be hydrolyzed by amygdalinase and can form very good complexes with metal atoms. Easily binds to metalloproteins and often significantly inhibits the function of metalloproteins, especially for cytochrome C oxidase, even at a concentration of 10-4M, which will strongly inhibit it, thus stopping breathing. At high concentrations, it binds to the carbonyl group of pyridoxal phosphate, etc., and inhibits the action of enzymes that use pyridoxal phosphate as a coenzyme. It also acts on the disulfide bond to reduce it (-S-S-+HCN→-SH+NC-S), so it can also inhibit the activity of papain.
In the generalized acid-base theory, the cyanide ion (CN-) is classified as a soft base, so it can form a strong bond with the low-valent heavy metal ions of soft acids. Based on this, cyanide is widely used in the hydrometallurgical smelting of gold and silver.
Cyanide is widely used in gold mining, because gold elemental substance reduces its oxidation potential due to the complexation of cyanide ions, so that it can be oxidized by oxygen in the air under alkaline conditions to form soluble gold salt, which can be dissolved. The gold is effectively separated from the slag, and then the gold is reduced from the solution to the metal through a displacement reaction with active metals such as zinc blocks (see hydrometallurgy).
Its toxicity is related to the super complex ability of CN ions to heavy metal ions. CN mainly combines with the ferric ions in the cytochrome P450, so that it loses the ability to transfer electrons in the respiratory chain, and then causes the poisoned person to die. Cyanide poisoning is generally very rapid. The commonly used clinical rescue method is to use sodium thiosulfate solution for intravenous injection, and at the same time make those conscious patients inhale isoamyl nitrite for vasodilation to overcome hypoxia. The common cause of cyanide poisoning is the accidental consumption of cyanide-containing nuts, such as bitter almonds and ginkgo. After being poisoned, it will give off a unique bitter almond smell.
Cause of poisoning
Inorganic and organic cyanide are widely used in industrial and agricultural production, especially the commonly used cyanide in the electroplating industry, so it is easy to obtain and is often used for suicide or homicide. People often eat a large amount of mishandled or untreated bitter almonds and cassava that cause accidental poisoning.
Cyanide enters the body and decomposes toxic cyanide ions (CN-). Cyanide ions can inhibit the activity of 42 enzymes in tissue cells, such as cytochrome oxidase, peroxidase, decarboxylase, succinate dehydrogenase and Lactate dehydrogenase and so on. Among them, cytochrome oxidase is the most sensitive to cyanide. Cyanide ions can quickly combine with ferric iron in oxidized cytochrome oxidase to prevent it from reducing to ferric iron, interrupting the oxidation process of transmitting electrons, and tissue cells cannot use the oxygen in the blood to cause internal asphyxia. The central nervous system is most sensitive to hypoxia, so the brain is damaged first, leading to death due to central respiratory failure. In addition, the hydroxide ions released by cyanide in the digestive tract have a corrosive effect. Those who inhale high concentrations of hydrogen cyanide or swallow a large amount of cyanide can stop breathing within 2-3 minutes and die in the form of "electric shock".
Toxic dose and lethal dose
The lethal dose of oral hydrocyanic acid is 0.7～3.5mg/kg; the concentration of hydrogen cyanide in the inhaled air reaches 0.3mg/L to be lethal; the lethal dose of oral sodium cyanide and potassium cyanide is 1～2mg/kg. Taking 40-60 tablets of bitter almonds for adults and 10-20 tablets for children can cause poisoning and even death. The lethal dose of untreated cassava is 150-300g. In addition, many cyanide-containing compounds (such as potassium cyanide, sodium cyanide and drugs used in electroplating and photographic dyes often contain cyanide) can cause acute poisoning.
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