Potassium cyanide: what is it and how does it work

The history of cyanides is confidently traced from almost the first written sources that have reached us. The ancient Egyptians, for example, used peach bones to obtain a deadly essence, which is simply called “peach” in papyrus exhibited in the Louvre.

Lethal Peach Synthesis

Peach, like two and a half hundred plants, including almonds, cherries, cherries, plums, belongs to the genus of plums. The seeds of the fruits of these plants contain the substance amygdalin - glycoside, which perfectly illustrates the concept of “lethal synthesis”. This term is not entirely correct, it would be more correct to call the phenomenon “lethal metabolism”: in its course, a harmless (and sometimes even useful) compound, under the action of enzymes and other substances, breaks down to a potent poison. In the stomach, amygdalin undergoes hydrolysis, and one molecule of glucose is split off from its molecule - prunazin is formed (some of it is contained in the seeds of berries and fruits initially). Further, enzyme systems (prunazin-β-glucosidase) are included in the work, which "bite off" the last remaining glucose, after which the mandelonitrile compound remains from the original molecule. In fact, this is a meta-compound that either sticks together into a single molecule, then again breaks up into components - benzaldehyde (a weak poison with a semi-lethal dose, that is, a dose that causes the death of half of the members of the test group, DL50 - 1.3 g / kg of rat body weight) and hydrocyanic acid (DL50 - 3.7 mg / kg rat body weight). It is these two substances in a pair that provide the characteristic smell of bitter almonds.

In the medical literature there is not a single confirmed case of death after eating peach or apricot kernels, although poisoning cases requiring hospitalization are described. And there is a rather simple explanation for this: only raw bones are needed for the formation of poison, but you can’t eat a lot of them. Why raw? In order for amygdalin to turn into hydrocyanic acid, enzymes are necessary, and under the influence of high temperature (sunlight, boiling, frying) they are denatured. So stewed fruit, jam and red-hot bones are completely safe. Purely theoretically, poisoning with tincture on fresh cherries or apricots is possible, since there are no denaturing factors in this case. But there another mechanism of neutralization of the resulting hydrocyanic acid comes into effect, described at the end of the article.

Color is heavenly, blue. Why is acid called hydrocyanic? The cyano group in combination with iron gives a saturated bright blue color. The most famous compound is Prussian blue, a mixture of hexacyanoferrates with the idealized formula Fe7 (CN) 18. It was from this dye that hydrogen cyanide was isolated in 1704. From it he obtained pure hydrocyanic acid and determined its structure in 1782 by the outstanding Swedish chemist Karl Wilhelm Scheele. According to legend, four years later, on the day of his wedding, Scheele died at his desk. Among the reagents surrounding it was HCN.

Military background

The effectiveness of cyanides for the targeted elimination of the enemy at all times beckoned the military. But large-scale experiments became possible only at the beginning of the 20th century, when methods for the production of cyanides in industrial quantities were developed.

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On July 1, 1916, the French first used hydrogen cyanide against German troops in battles near the Somme River. However, the attack failed: HCN vapors are lighter than air and quickly evaporated at high temperature, so the “chlorine” focus with an ominous cloud spreading on the ground could not be repeated. Attempts to weight cyanide with arsenic trichloride, chlorine tin and chloroform were unsuccessful, so the use of cyanides had to be forgotten. More precisely, postpone - until the Second World War.

The German chemical school and the chemical industry at the beginning of the 20th century were unparalleled. Outstanding scientists, including the 1918 Nobel laureate, Fritz Gaber, worked for the good of the country. Under his leadership, a group of researchers from the freshly created German Pest Control Society (Degesch) modified hydrocyanic acid, which has been used as a fumigant since the late 19th century. To reduce the volatility of the compounds, German chemists used an adsorbent. Before use, the granules should be immersed in water to release the insecticide accumulated in them. The product is called the Cyclone. In 1922, Degesch became the sole owner of Degussa. In 1926, a patent was registered for a development team for a second, very successful version of the insecticide - Cyclone B, which was distinguished by a more powerful sorbent, the presence of a stabilizer, as well as an irritant that caused eye irritation - to avoid accidental poisoning.

Meanwhile, Gaber has actively promoted the idea of ​​chemical weapons since the time of the First World War, and many of its developments had purely military significance. “If soldiers die in a war, then what difference does it make, ” he said. Gaber’s scientific and business career was steadily uphill, and he naively believed that his merits with Germany had long made him a full-fledged German. However, for the Nazis who were gaining strength, he was primarily a Jew. Gaber began to look for work in other countries, but, despite all his scientific achievements, many scientists did not forgive him the development of chemical weapons. Nevertheless, in 1933, Gaber and his family went to France, then to Spain, then to Switzerland, where he died in January 1934, fortunately for himself not having time to see for what purpose the Nazis used Cyclone B.

Modus operandi

Hydrocyanic acid vapors are not very effective as poison by inhalation, but when ingested with its salts DL50 - only 2.5 mg / kg body weight (for potassium cyanide). Cyanides block the last stage of the transfer of protons and electrons by a chain of respiratory enzymes from oxidized substrates to oxygen, that is, they stop cellular respiration. This process is not fast - minutes even at ultrahigh doses. But the cinema, showing the rapid action of cyanides, is not lying: the first phase of poisoning - loss of consciousness - really sets in after a few seconds. The agony lasts for several more minutes - convulsions, rise and fall in blood pressure, and only then does respiratory arrest and cardiac activity stop.

At lower doses, you can even track several periods of poisoning. First, a bitter taste and burning sensation in the mouth, salivation, nausea, headache, rapid breathing, impaired coordination of movements, increasing weakness. A painful shortness of breath later joins, oxygen is not enough for the tissues, so the brain gives a command to increase and deepen breathing (this is a very characteristic symptom). Gradually, breathing is inhibited, another characteristic symptom appears - a short breath and a very long exhale. Pulse becomes rarer, pressure drops, pupils dilate, skin and mucous membranes turn pink, and do not turn blue or turn pale, as in other cases of hypoxia. If the dose is non-fatal, this is all and is limited, after a few hours the symptoms disappear. Otherwise, the turn of loss of consciousness and seizures occurs, and then arrhythmia occurs, cardiac arrest is possible. Sometimes paralysis and a long (up to several days) coma develop.

It does not cure, but cripples! Amygdalin is popular with near-medical quacks who call themselves representatives of alternative medicine. Since 1961, under the brand name “Laetrile” or under the name “Vitamin B17, ” the semi-synthetic analogue of amygdalin has been actively promoted as a “treatment for cancer." There is no scientific basis for this. In 2005, in the journal Annals of Pharmacotherapy, a case of severe cyanide poisoning was described: a 68-year-old patient took Laetrile, as well as vitamin C hyperdoses, hoping to increase the prophylactic effect. As it turned out, such a combination leads exactly in the opposite direction from health.

Poisoned - Poison

Cyanides have a very high affinity for ferric iron, which is why they rush into cells for respiratory enzymes. So the idea of ​​a “decoy duck” for poison was in the air. It was first implemented in 1929 by Romanian researchers Mladoveanu and Gheorghiu, who first poisoned the dog with a lethal dose of cyanide and then saved it by intravenous administration of sodium nitrite. This is now the food supplement E250 is being deceived by everyone who is not lazy, but the animal, by the way, has survived: sodium nitrite in conjunction with hemoglobin forms methemoglobin, on which cyanides in the blood “peck” better than respiratory enzymes, for which you still need to get inside cells.

Nitrites oxidize hemoglobin very quickly, so one of the most effective antidotes (antidotes) - amyl nitrite, isoamyl ester of nitrous acid - just breathe in with fleece, like ammonia. Later it turned out that methemoglobin not only binds the cyanide ions circulating in the blood, but also unlocks the respiratory enzymes that they have “closed” with them. The group of methemoglobin formers, albeit already slower, also includes methylene blue dye (known as “blue”).

There is a flip side to the coin: when administered intravenously, nitrites themselves become poisons. So to saturate the blood with methemoglobin is possible only with strict control of its content, not more than 25-30% of the total mass of hemoglobin. There is one more nuance: the binding reaction is reversible, that is, after a while the complex formed will decompose and the cyanide ions will rush into the cells of their traditional targets. So we need another line of defense, for example, cobalt compounds (cobalt salt of ethylenediaminetetraacetic acid, hydroxycobalamin - one of the B12 vitamins), as well as the anticoagulant heparin, beta-hydroxyethylmethyleneamine, hydroquinone, sodium thiosulfate.

Almonds and other amygdalin are found in plants of the Rosaceae family (plum genus - cherry, cherry plum, sakura, sweet cherry, peach, apricot, almond, bird cherry, plum), as well as in the representatives of the family cereals, legumes, adoxic (elderberry genus), flax (genus elderberry) flax), euphorbiaceae (genus of cassava). Amygdalin content in berries and fruits depends on many different factors. So, in apple seeds it can be from 1 to 4 mg / kg. In freshly squeezed apple juice - 0.01-0.04 mg / ml, and in packaged juice - 0.001-0.007 ml / ml. For comparison: apricot kernels contain 89−2170 mg / kg.

Case of Rasputin

But the most interesting antidote is much simpler and more affordable. Chemists at the end of the XIX century noticed that cyanides are converted into non-toxic compounds when interacting with sugar (this is especially effective in solution). The mechanism of this phenomenon in 1915 was explained by German scientists Rupp and Goltze: cyanides, reacting with substances containing an aldehyde group, form cyanohydrins. There are such groups in glucose, and amygdalin, mentioned at the beginning of the article, is essentially a glucose-neutralized cyanide.

If Prince Yusupov or one of the conspirators who had joined him, Purishkevich or Grand Duke Dmitry Pavlovich, knew about this, they would not start filling cakes (where sucrose was already hydrolyzed to glucose) and wine (where glucose is also available), intended for treats of Grigory Rasputin, potassium cyanide. However, there is an opinion that he was not poisoned at all, and the story about the poison appeared to confuse the investigation. No poison was found in the stomach of the “royal friend”, but that absolutely does not mean anything - no one was looking for cyanohydrins there.

Glucose has its advantages: for example, it is able to restore hemoglobin. This is very useful for "picking up" detachable cyanide ions when using nitrites and other "toxic antidotes." There is even a finished drug, “chromosmon” - a 1% solution of methylene blue in a 25% glucose solution. But there are annoying cons. First, cyanohydrins form slowly, much more slowly than methemoglobin. Secondly, they are formed only in the blood and only before the poison enters the cells to the respiratory enzymes. In addition, it will not work to bite potassium cyanide with a piece of sugar: sucrose does not react directly with cyanides, it is necessary that it first breaks down into glucose with fructose. So if you are afraid of cyanide poisoning, it is better to carry an amyl nitrite ampoule with you - crush it in a scarf and breathe 10-15 s. And then you can call an ambulance and complain that you were poisoned with cyanide. Doctors will be surprised!

The author of the article is a toxicologist, scientific editor of the journal Russian Pharmacies

The article “With the smell of bitter almonds” was published in the journal Popular Mechanics (No. 1, January 2016). Do you like the article?

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