Poisoning with arsenic and its salts - a lethal dose for humans, symptoms, treatment. Chemical properties of arsenic Where is arsenic used?

Natural compounds of Arsenic with sulfur (orpiment As 2 S 3, realgar As 4 S 4) were known to the peoples of the ancient world, who used these minerals as medicines and paints. The product of burning Arsenic sulfides was also known - Arsenic (III) oxide As 2 O 3 (“white Arsenic”). The name arsenikon is found already in Aristotle; it is derived from the Greek arsen - strong, courageous and served to designate Arsenic compounds (due to their strong effect on the body). The Russian name is believed to come from “mouse” (after the use of Arsenic preparations to exterminate mice and rats). The production of Arsenic in a free state is attributed to Albertus Magnus (around 1250). In 1789, A. Lavoisier included Arsenic in the list of chemical elements.

Distribution of Arsenic in nature. The average content of arsenic in the earth's crust (clarke) is 1.7·10 -4% (by mass), in such quantities it is present in most igneous rocks. Since Arsenic compounds are volatile at high temperatures, the element does not accumulate during magmatic processes; it concentrates, precipitating from hot deep waters (together with S, Se, Sb, Fe, Co, Ni, Cu and other elements). During volcanic eruptions, Arsenic enters the atmosphere in the form of its volatile compounds. Since Arsenic is multivalent, its migration is greatly influenced by the redox environment. Under oxidizing conditions of the earth's surface, arsenates (As 5+) and arsenites (As 3+) are formed. These are rare minerals found only in areas of Arsenic deposits. Native Arsenic and As 2+ minerals are even less common. Of the numerous Arsenic minerals (about 180), only arsenopyrite FeAsS is of primary industrial importance.

Small amounts of Arsenic are necessary for life. However, in areas of Arsenic deposits and the activity of young volcanoes, soils in some places contain up to 1% Arsenic, which is associated with livestock diseases and death of vegetation. The accumulation of Arsenic is especially typical for landscapes of steppes and deserts, in the soils of which Arsenic is inactive. In humid climates, Arsenic is easily washed out of the soil.

In living matter there is an average of 3·10 -5% Arsenic, in rivers 3·10 -7%. Arsenic carried by rivers into the ocean precipitates relatively quickly. In sea water there is only 1·10 -7% Arsenic, but in clays and shales it is 6.6·10 -4%. Sedimentary iron ores and ferromanganese nodules are often enriched in Arsenic.

Physical properties of Arsenic. Arsenic has several allotropic modifications. Under normal conditions, the most stable is the so-called metallic, or gray, Arsenic (α-As) - a gray-steel brittle crystalline mass; when freshly fractured, it has a metallic luster; in air it quickly becomes dull, as it is covered with a thin film of As 2 O 3 . The crystal lattice of gray Arsenic is rhombohedral (a = 4.123Å, angle α = 54°10", x == 0.226), layered. Density 5.72 g/cm 3 (at 20 °C), electrical resistivity 35·10 -8 ohm m, or 35 10 -6 ohm cm, temperature coefficient of electrical resistance 3.9 10 -3 (0°-100 °C), Brinell hardness 1470 MN/m 2, or 147 kgf/mm 2 (3 -4 according to Moocy); Arsenic is diamagnetic. Under atmospheric pressure, Arsenic sublimes at 615 °C without melting, since the triple point α-As lies at 816 °C and a pressure of 36 at. Arsenic vapor consists of up to 800 °C As 4 molecules, above 1700 °C - only from As 2. When Arsenic vapor condenses on a surface cooled by liquid air, yellow Arsenic is formed - transparent, soft as wax crystals, with a density of 1.97 g/cm 3, similar in properties to white phosphorus. light or upon slight heating it turns into gray Arsenic. Glassy-amorphous modifications are also known: black Arsenic and brown Arsenic, which when heated above 270 ° C turn into gray Arsenic

Chemical properties of Arsenic. The configuration of the outer electrons of the Arsenic atom is 3d 10 4s 2 4p 3. In compounds, Arsenic has oxidation states +5, +3 and -3. Gray Arsenic is much less chemically active than phosphorus. When heated in air above 400 °C, arsenic burns, forming As 2 O 3. Arsenic combines directly with halogens; under normal conditions, AsF 5 is a gas; AsF 3, AsCl 3, AsBr 3 - colorless, highly volatile liquids; AsI 3 and As 2 I 4 are red crystals. When arsenic is heated with sulfur, sulfides are obtained: orange-red As 4 S 4 and lemon-yellow As 2 S 3. Pale yellow sulfide As 2 S 5 is precipitated by passing H 2 S into an ice-cooled solution of arsenic acid (or its salts) in fuming hydrochloric acid: 2H 3 AsO 4 + 5H 2 S = As 2 S 5 + 8H 2 O; At about 500 °C it decomposes into As 2 S 3 and sulfur. All Arsenic sulfides are insoluble in water and dilute acids. Strong oxidizing agents (mixtures of HNO 3 + HCl, HCl + KClO 3) convert them into a mixture of H 3 AsO 4 and H 2 SO 4. As 2 S 3 sulfide easily dissolves in sulfides and polysulfides of ammonium and alkali metals, forming salts of acids - thioarsenic H 3 AsS 3 and thioarsenic H 3 AsS 4 . With oxygen, Arsenic produces oxides: Arsenic (III) oxide As 2 O 3 - arsenous anhydride and Arsenic (V) oxide As 2 O 5 - arsenic anhydride. The first of them is formed by the action of oxygen on Arsenic or its sulfides, for example 2As 2 S 3 + 9O 2 = 2As 2 O 3 + 6SO 2. As 2 O 3 vapors condense into a colorless glassy mass, which becomes opaque over time due to the formation of small cubic crystals, density 3.865 g/cm 3 . The vapor density corresponds to the formula As 4 O 6; above 1800 °C the steam consists of As 2 O 3. 2.1 g of As 2 O 3 dissolves in 100 g of water (at 25 °C). Arsenic (III) oxide is an amphoteric compound with a predominance of acidic properties. Salts (arsenites) corresponding to orthoarsenic acids H 3 AsO 3 and metaarsenic HAsO 2 are known; the acids themselves have not been obtained. Only alkali metal and ammonium arsenites are soluble in water. As 2 O 3 and arsenites are usually reducing agents (for example, As 2 O 3 + 2I 2 + 5H 2 O = 4HI + 2H 3 AsO 4), but can also be oxidizing agents (for example, As 2 O 3 + 3C = 2As + 3SO ).

Arsenic (V) oxide is obtained by heating arsenic acid H 3 AsO 4 (about 200 ° C). It is colorless, at about 500 °C it decomposes into As 2 O 3 and O 2. Arsenic acid is obtained by the action of concentrated HNO 3 on As or As 2 O 3. Arsenic acid salts (arsenates) are insoluble in water, with the exception of alkali metal and ammonium salts. Salts are known that correspond to the acids orthoarsenic H 3 AsO 4 , metaarsenic HAsO 3 and pyroarsenic H 4 As 2 O 7 ; the last two acids were not obtained in a free state. When alloyed with metals, Arsenic mostly forms compounds (arsenides).

Getting Arsenic. Arsenic is produced industrially by heating arsenic pyrites:

FeAsS = FeS + As

or (less often) reduction of As 2 O 3 with coal. Both processes are carried out in retorts made of refractory clay connected to a receiver for condensation of Arsenic vapor. Arsenic anhydride is obtained by oxidative roasting of arsenic ores or as a by-product of roasting polymetallic ores, which almost always contain arsenic. During oxidative roasting, As 2 O 3 vapors are formed, which condense in the collection chambers. Crude As 2 O 3 is purified by sublimation at 500-600 °C. Purified As 2 O 3 is used for the production of Arsenic and its preparations.

Use of Arsenic. Small additions of Arsenic (0.2-1.0% by weight) are added to lead used for the production of shotgun shot (Arsenic increases the surface tension of molten lead, due to which the shot acquires a shape close to spherical; Arsenic slightly increases the hardness of lead). As a partial substitute for antimony, Arsenic is included in some babbitt and printing alloys.

Pure Arsenic is not poisonous, but all its compounds that are soluble in water or can go into solution under the action of gastric juice are extremely poisonous; Arsenic hydrogen is especially dangerous. Of the arsenic compounds used in production, arsenous anhydride is the most toxic. Arsenic admixture is contained in almost all sulfide ores of non-ferrous metals, as well as iron (sulfur) pyrites. Therefore, during their oxidative roasting, along with sulfur dioxide SO 2, As 2 O 3 is always formed; Most of it condenses in the smoke channels, but in the absence or low efficiency of treatment facilities, the exhaust gases of ore kilns carry away noticeable amounts of As 2 O 3. Pure Arsenic, although not poisonous, is always covered with a coating of poisonous As 2 O 3 when stored in air. In the absence of proper ventilation, etching of metals (iron, zinc) with industrial sulfuric or hydrochloric acids containing arsenic is extremely dangerous, since this produces arsenous hydrogen.

Arsenic in the body. As a trace element, Arsenic is ubiquitous in living nature. The average content of Arsenic in soils is 4·10 -4%, in plant ash - 3·10 -5%. The Arsenic content in marine organisms is higher than in terrestrial organisms (in fish 0.6-4.7 mg per 1 kg of raw material, accumulates in the liver). The average content of Arsenic in the human body is 0.08-0.2 mg/kg. In the blood, Arsenic is concentrated in red blood cells, where it binds to the hemoglobin molecule (and the globin fraction contains twice as much as heme). The largest amount of it (per 1 g of tissue) is found in the kidneys and liver. A lot of Arsenic is found in the lungs and spleen, skin and hair; relatively little - in the cerebrospinal fluid, brain (mainly the pituitary gland), gonads and others. In tissues, arsenic is found in the main protein fraction, much less in the acid-soluble fraction, and only a small part of it is found in the lipid fraction. Arsenic is involved in redox reactions: oxidative breakdown of complex carbohydrates, fermentation, glycolysis, etc. Arsenic compounds are used in biochemistry as specific enzyme inhibitors to study metabolic reactions.

The content of the article

ARSENIC– a chemical element of group V of the periodic table, belongs to the nitrogen family. Relative atomic mass 74.9216. In nature, arsenic is represented by only one stable nuclide 75 As. More than ten of its radioactive isotopes with half-lives from several minutes to several months have also been artificially obtained. Typical oxidation states in compounds are –3, +3, +5. The name of arsenic in Russian is associated with the use of its compounds to exterminate mice and rats; The Latin name Arsenicum comes from the Greek “arsen” - strong, powerful.

Historical information.

Arsenic belongs to the five “alchemical” elements discovered in the Middle Ages (surprisingly, four of them - As, Sb, Bi and P - are in the same group of the periodic table - the fifth). At the same time, arsenic compounds have been known since ancient times; they were used to produce paints and medicines. Particularly interesting is the use of arsenic in metallurgy.

Several thousand years ago, the Stone Age gave way to the Bronze Age. Bronze is an alloy of copper and tin. Historians believe that the first bronze was cast in the Tigris-Euphrates valley, somewhere between the 30th and 25th centuries. BC. In some regions, bronze with especially valuable properties was smelted - it was better cast and easier to forge. As modern scientists have found, it was a copper alloy containing from 1 to 7% arsenic and no more than 3% tin. Probably, at first, during its smelting, the rich copper ore malachite was confused with the weathering products of some also green sulfide copper-arsenic minerals. Having appreciated the remarkable properties of the alloy, the ancient craftsmen then specifically looked for arsenic minerals. For the search, we used the property of such minerals to give off a specific garlic odor when heated. However, over time, the smelting of arsenic bronze ceased. Most likely this happened due to frequent poisoning during the firing of arsenic-containing minerals.

Of course, arsenic was known in the distant past only in the form of its minerals. Thus, in Ancient China, the solid mineral realgar (a sulfide of the composition As 4 S 4, realgar in Arabic means “mine dust”) was used for stone carving, but when heated or exposed to light it “deteriorated”, as it turned into As 2 S 3. In the 4th century. BC. Aristotle described this mineral under the name "sandarac". In the 1st century AD The Roman writer and scientist Pliny the Elder, and the Roman physician and botanist Dioscorides described the mineral orpiment (arsenic sulfide As 2 S 3). Translated from Latin, the name of the mineral means “golden paint”: it was used as a yellow dye. In the 11th century alchemists distinguished three “varieties” of arsenic: the so-called white arsenic (As 2 O 3 oxide), yellow arsenic (As 2 S 3 sulfide) and red arsenic (As 4 S 4 sulfide). White arsenic was obtained by sublimation of arsenic impurities during the roasting of copper ores containing this element. Condensing from the gas phase, arsenic oxide settled in the form of a white coating. White arsenic has been used since ancient times to kill pests, as well as...

In the 13th century Albert von Bolstedt (Albert the Great) obtained a metal-like substance by heating yellow arsenic with soap; This may have been the first example of arsenic in the form of a simple substance obtained artificially. But this substance violated the mystical “connection” of the seven known metals with the seven planets; This is probably why alchemists considered arsenic a “bastard metal.” At the same time, they discovered its property of giving copper a white color, which gave rise to calling it “a Venus (i.e. copper) bleaching agent.”

Arsenic was clearly identified as an individual substance in the mid-17th century, when the German pharmacist Johann Schroeder obtained it in a relatively pure form by reducing the oxide with charcoal. Later, the French chemist and physician Nicolas Lemery obtained arsenic by heating a mixture of its oxide with soap and potash. In the 18th century arsenic was already well known as an unusual "semi-metal". In 1775, the Swedish chemist K.V. Scheele obtained arsenic acid and gaseous arsenic hydrogen, and in 1789 A.L. Lavoisier finally recognized arsenic as an independent chemical element. In the 19th century organic compounds containing arsenic were discovered.

Arsenic in nature.

There is little arsenic in the earth's crust - about 5·10 -4% (that is, 5 g per ton), approximately the same as germanium, tin, molybdenum, tungsten or bromine. Arsenic is often found in minerals together with iron, copper, cobalt, and nickel.

The composition of minerals formed by arsenic (and about 200 of them are known) reflects the “semi-metallic” properties of this element, which can be in both positive and negative oxidation states and combine with many elements; in the first case, arsenic can play the role of a metal (for example, in sulfides), in the second - a non-metal (for example, in arsenides). The complex composition of a number of arsenic minerals reflects its ability, on the one hand, to partially replace sulfur and antimony atoms in the crystal lattice (ionic radii S–2, Sb–3 and As–3 are close and are 0.182, 0.208 and 0.191 nm, respectively), on the other – metal atoms. In the first case, arsenic atoms have a rather negative oxidation state, in the second - a positive one.

The electronegativity of arsenic (2.0) is small, but higher than that of antimony (1.9) and most metals, therefore the –3 oxidation state is observed for arsenic only in metal arsenides, as well as in stibarsen SbAs and intergrowths of this mineral with pure crystals antimony or arsenic (mineral allemontite). Many arsenic compounds with metals, judging by their composition, are intermetallic compounds rather than arsenides; some of them have variable arsenic content. Arsenides may simultaneously contain several metals, the atoms of which, at close ion radii, replace each other in the crystal lattice in arbitrary ratios; in such cases, in the mineral formula, the symbols of the elements are listed separated by commas. All arsenides have a metallic luster; they are opaque, heavy minerals, and their hardness is low.

Examples of natural arsenides (about 25 of them are known) are the minerals löllingite FeAs 2 (an analogue of pyrite FeS 2), skutterudite CoAs 2–3 and nickel skutterudite NiAs 2–3, nickel (red nickel pyrite) NiAs, rammelsbergite (white nickel pyrite) NiAs 2 , safflorite (speys cobalt) CoAs 2 and clinosafflorite (Co,Fe,Ni)As 2, langisite (Co,Ni)As, sperrylite PtAs 2, maucherite Ni 11 As 8, oregonite Ni 2 FeAs 2, algodonite Cu 6 As. Due to their high density (more than 7 g/cm3), geologists classify many of them as “super-heavy” minerals.

The most common arsenic mineral is arsenopyrite (arsenic pyrite). FeAsS can be considered as a product of the replacement of sulfur in FeS 2 pyrite with arsenic atoms (ordinary pyrite also always contains a little arsenic). Such compounds are called sulfosalts. Similarly, the minerals cobaltine (cobalt luster) CoAsS, glaucodote (Co,Fe)AsS, gersdorfite (nickel luster) NiAsS, enargite and luzonite of the same composition, but different structures Cu 3 AsS 4, proustite Ag 3 AsS 3 - an important silver ore, which Sometimes called "ruby silver" because of its bright red color, it is often found in the upper layers of silver veins, where magnificent large crystals of this mineral are found. Sulfosalts may also contain noble metals of the platinum group; These are the minerals osarsite (Os,Ru)AsS, ruarsite RuAsS, irarsite (Ir,Ru,Rh,Pt)AsS, platarsite (Pt,Rh,Ru)AsS, hollingworthite (Rd,Pt,Pd)AsS. Sometimes the role of sulfur atoms in such double arsenides is played by antimony atoms, for example, in seinajokite (Fe,Ni)(Sb,As) 2, arsenopalladinite Pd 8 (As,Sb) 3, arsene polybasite (Ag,Cu) 16 (Ar,Sb) 2 S 11.

The structure of minerals is interesting, in which arsenic is present simultaneously with sulfur, but plays rather the role of a metal, grouping together with other metals. These are the minerals arsenosulvanite Cu 3 (As,V)S 4, arsenogauchekornite Ni 9 BiAsS 8, freibergite (Ag,Cu,Fe) 12 (Sb,As) 4 S 13, tennantite (Cu,Fe) 12 As 4 S 13, argentotennantite (Ag,Cu) 10 (Zn,Fe) 2 (As,Sb) 4 S 13, goldfieldite Cu 12 (Te,Sb,As) 4 S 13, gyrodite (Cu,Zn,Ag) 12 (As,Sb) 4 (Se,S) 13 . You can imagine what a complex structure the crystal lattice of all these minerals has.

Arsenic has a clearly positive oxidation state in natural sulfides - yellow orpiment As 2 S 3 , orange-yellow dimorphite As 4 S 3 , orange-red realgar As 4 S 4 , carmine-red getchellite AsSbS 3 , as well as in colorless oxide As 2 O 3, which occurs as the minerals arsenolite and claudetite with different crystal structures (they are formed as a result of weathering of other arsenic minerals). Typically these minerals are found in the form of small inclusions. But in the 30s of the 20th century. In the southern part of the Verkhoyansk Range, huge crystals of orpiment measuring up to 60 cm in size and weighing up to 30 kg were found.

In natural salts of arsenic acid H 3 AsO 4 - arsenates (about 90 of them are known), the oxidation state of arsenic is +5; examples include bright pink erythrin (cobalt color) Co 3 (AsO 4) 2 8H 2 O, green annabergite Ni 3 (AsO 4) 2 8H 2 O, scorodite Fe III AsO 4 2H 2 O and simplesite Fe II 3 (AsO 4) 2 8H 2 O, brown-red gasparite (Ce,La,Nd)ArO 4, colorless goernesite Mg 3 (AsO 4) 2 8H 2 O, rooseveltite BiAsO 4 and kettigite Zn 3 (AsO 4) 2 8H 2 O, as well as many basic salts, for example, olivenite Cu 2 AsO 4 (OH), arsenobismite Bi 2 (AsO 4)(OH) 3. But natural arsenites - derivatives of arsenic acid H 3 AsO 3 - are very rare.

In central Sweden there are the famous Langbanov iron-manganese quarries, in which more than 50 samples of arsenate minerals were found and described. Some of them are not found anywhere else. They were once formed as a result of the reaction of arsenic acid H 3 AsO 4 with pyrocroite Mn(OH) 2 at not very high temperatures. Typically, arsenates are oxidation products of sulfide ores. They, as a rule, have no industrial use, but some of them are very beautiful and adorn mineralogical collections.

In the names of numerous arsenic minerals one can find place names (Lölling in Austria, Freiberg in Saxony, Seinäjoki in Finland, Skutterud in Norway, Allemon in France, the Canadian Langis mine and Getchell mine in Nevada, Oregon in the USA, etc.), the names of geologists, chemists, politicians, etc. (German chemist Karl Rammelsberg, Munich mineral trader William Maucher, mine owner Johann von Gersdorff, French chemist F. Claudet, English chemists John Proust and Smithson Tennant, Canadian chemist F. L. Sperry, US President Roosevelt, etc.), names of plants (thus, the name of the mineral safflorite comes from saffron), the initial letters of the names of the elements - arsenic, osmium, ruthenium, iridium, palladium, platinum, Greek roots (“erythros” - red, “enargon” - visible, “lithos” - stone) and etc. and so on.

An interesting ancient name for the mineral nickel (NiAs) is kupfernickel. Medieval German miners called Nickel the evil mountain spirit, and “kupfernickel” (Kupfernickel, from German Kupfer - copper) - “damn copper”, “fake copper”. The copper-red crystals of this ore looked very much like copper ore; It was used in glass making to color glass green. But no one was able to get copper from it. This ore was studied by the Swedish mineralogist Axel Kronstedt in 1751 and isolated a new metal from it, calling it nickel.

Since arsenic is chemically quite inert, it is also found in its native state - in the form of fused needles or cubes. Such arsenic usually contains from 2 to 16% impurities - most often these are Sb, Bi, Ag, Fe, Ni, Co. It is easy to grind into powder. In Russia, geologists found native arsenic in Transbaikalia, in the Amur region, and it is also found in other countries.

Arsenic is unique in that it is found everywhere - in minerals, rocks, soil, water, plants and animals, and it is not for nothing that it is called “ubiquitous.” The distribution of arsenic over different regions of the globe was largely determined during the formation of the lithosphere by the volatility of its compounds at high temperatures, as well as by the processes of sorption and desorption in soils and sedimentary rocks. Arsenic migrates easily, which is facilitated by the fairly high solubility of some of its compounds in water. In humid climates, arsenic is washed out of the soil and carried away by groundwater and then by rivers. The average arsenic content in rivers is 3 µg/l, in surface waters – about 10 µg/l, in sea and ocean waters – only about 1 µg/l. This is explained by the relatively rapid precipitation of its compounds from water with accumulation in bottom sediments, for example, in ferromanganese nodules.

In soils, the arsenic content is usually from 0.1 to 40 mg/kg. But in areas where arsenic ores occur, as well as in volcanic areas, the soil can contain a lot of arsenic - up to 8 g/kg, as in some areas of Switzerland and New Zealand. In such places, vegetation dies and animals get sick. This is typical for steppes and deserts, where arsenic is not washed out of the soil. Clay rocks are also enriched compared to the average content - they contain four times more arsenic than the average. In our country, the maximum permissible concentration of arsenic in soil is 2 mg/kg.

Arsenic can be carried out of the soil not only by water, but also by wind. But to do this, it must first turn into volatile organoarsenic compounds. This transformation occurs as a result of the so-called biomethylation - the addition of a methyl group to form a C–As bond; this enzymatic process (it is well known for mercury compounds) occurs with the participation of the coenzyme methylcobalamin, a methylated derivative of vitamin B 12 (it is also found in the human body). Biomethylation of arsenic occurs in both fresh and sea water and leads to the formation of organoarsenic compounds - methylarsonic acid CH 3 AsO(OH) 2, dimethylarsine (dimethylarsenic, or cacodylic) acid (CH 3) 2 As(O)OH, trimethylarsine ( CH 3) 3 As and its oxide (CH 3) 3 As = O, which also occur in nature. Using 14 C-labeled methylcobalamin and 74 As-labeled sodium hydroarsenate Na 2 HAsO 4 it was shown that one of the strains of methanobacteria reduces and methylates this salt to volatile dimethylarsine. As a result, the air in rural areas contains an average of 0.001 - 0.01 μg/m 3 of arsenic, in cities where there is no specific pollution - up to 0.03 μg/m 3, and near sources of pollution (non-ferrous metal smelting plants, power plants, working on coal with a high arsenic content, etc.) the concentration of arsenic in the air can exceed 1 μg/m 3 . The intensity of arsenic deposition in areas where industrial centers are located is 40 kg/km 2 per year.

The formation of volatile arsenic compounds (trimethylarsine, for example, boils at only 51 ° C) caused in the 19th century. numerous poisonings, since arsenic was contained in plaster and even green wallpaper paint. Scheele greens were previously used in the form of paint Cu 3 (AsO 3) 2 n H 2 O and Parisian or Schweyfurt greens Cu 4 (AsO 2) 6 (CH 3 COO) 2. In conditions of high humidity and the appearance of mold, volatile organoarsenic derivatives are formed from such paint. It is believed that this process could be the reason for the slow poisoning of Napoleon in the last years of his life (as is known, arsenic was found in Napoleon's hair a century and a half after his death).

Arsenic is found in noticeable quantities in some mineral waters. Russian standards establish that arsenic in medicinal table mineral waters should not exceed 700 µg/l. IN Jermuk it may be several times larger. Drinking one or two glasses of “arsenic” mineral water will not bring harm to a person: in order to be fatally poisoned, you need to drink three hundred liters at once... But it is clear that such water cannot be drunk constantly instead of ordinary water.

Chemists have found that arsenic in natural waters can be found in different forms, which is significant from the point of view of its analysis, migration methods, as well as the different toxicity of these compounds; Thus, compounds of trivalent arsenic are 25–60 times more toxic than pentavalent arsenic. As(III) compounds in water are usually present in the form of weak arsenic acid H 3 AsO 3 ( rK a = 9.22), and the As(V) compound - in the form of much stronger arsenic acid H 3 AsO 4 ( rK a = 2.20) and its deprotonated anions H 2 AsO 4 – and HAsO 4 2–.

Living matter contains an average of 6·10–6% arsenic, that is, 6 µg/kg. Some seaweeds can concentrate arsenic to such an extent that they become dangerous to humans. Moreover, these algae can grow and reproduce in pure solutions of arsenic acid. Such algae are used in some Asian countries as a remedy against rats. Even in the clear waters of the Norwegian fjords, algae can contain up to 0.1 g/kg of arsenic. In humans, arsenic is found in brain tissue and muscles, and it accumulates in hair and nails.

Properties of arsenic.

Although arsenic looks like a metal, it is still rather a non-metal: it does not form salts, for example, with sulfuric acid, but is itself an acid-forming element. Therefore, this element is often called a semimetal. Arsenic exists in several allotropic forms and in this respect is very similar to phosphorus. The most stable of them is gray arsenic, a very brittle substance that, when freshly fractured, has a metallic sheen (hence the name “metallic arsenic”); its density is 5.78 g/cm3. When heated strongly (up to 615° C), it sublimes without melting (the same behavior is characteristic of iodine). Under a pressure of 3.7 MPa (37 atm), arsenic melts at 817 ° C, which is significantly higher than the sublimation temperature. The electrical conductivity of gray arsenic is 17 times less than that of copper, but 3.6 times higher than that of mercury. As the temperature increases, its electrical conductivity, like that of typical metals, decreases - to approximately the same extent as that of copper.

If arsenic vapor is very quickly cooled to the temperature of liquid nitrogen (–196 ° C), a transparent soft yellow substance is obtained, reminiscent of yellow phosphorus, its density (2.03 g/cm 3) is significantly lower than that of gray arsenic. Arsenic vapor and yellow arsenic consist of As 4 molecules that have the shape of a tetrahedron - and here the analogy with phosphorus. At 800° C, a noticeable dissociation of vapor begins with the formation of As 2 dimers, and at 1700° C only As 2 molecules remain. When heated and exposed to ultraviolet light, yellow arsenic quickly turns gray with the release of heat. When arsenic vapor condenses in an inert atmosphere, another amorphous form of this element, black in color, is formed. If arsenic vapor is deposited on glass, a mirror film is formed.

The structure of the outer electron shell of arsenic is the same as that of nitrogen and phosphorus, but unlike them, it has 18 electrons in the penultimate shell. Like phosphorus, it can form three covalent bonds (4s 2 4p 3 configuration), leaving a lone pair on the As atom. The sign of the charge on the As atom in compounds with covalent bonds depends on the electronegativity of neighboring atoms. The participation of a lone pair in complex formation is significantly more difficult for arsenic compared to nitrogen and phosphorus.

If d orbitals are involved in the As atom, pairing of 4s electrons is possible to form five covalent bonds. This possibility is practically realized only in combination with fluorine - in pentafluoride AsF 5 (pentachloryl AsCl 5 is also known, but it is extremely unstable and quickly decomposes even at –50 ° C).

In dry air, arsenic is stable, but in humid air it fades and becomes covered with black oxide. During sublimation, arsenic vapor easily burns in air with a blue flame to form heavy white vapor of arsenic anhydride As 2 O 3. This oxide is one of the most common arsenic-containing reagents. It has amphoteric properties:

As 2 O 3 + 6HCl ® 2AsCl 3 + 3H 2 O,

2 O 3 + 6NH 4 OH ® 2(NH 4) 3 AsO 3 + 3H 2 O.

The oxidation of As 2 O 3 produces an acidic oxide - arsenic anhydride:

As 2 O 3 + 2HNO 3 ® As 2 O 5 + H 2 O + NO 2 + NO.

When it reacts with soda, sodium hydroarsenate is obtained, which is used in medicine:

As 2 O 3 + 2Na 2 CO 3 + H 2 O ® 2Na 2 HAsO 4 + 2CO 2 .

Pure arsenic is quite inert; water, alkalis and acids that do not have oxidizing properties do not affect it. Dilute nitric acid oxidizes it to orthoarsenic acid H 3 AsO 3 , and concentrated nitric acid oxidizes it to orthoarsenic acid H 3 AsO 4:

3As + 5HNO 3 + 2H 2 O ® 3H 3 AsO 4 + 5NO.

Arsenic(III) oxide reacts similarly:

3As 2 O 3 + 4HNO 3 + 7H 2 O ® 6H 3 AsO 4 + 4NO.

Arsenic acid is a medium-strength acid, slightly weaker than phosphoric acid. In contrast, arsenic acid is very weak, corresponding in strength to boric acid H 3 BO 3. In its solutions there is an equilibrium H 3 AsO 3 HAsO 2 + H 2 O. Arsenous acid and its salts (arsenites) are strong reducing agents:

HAsO 2 + I 2 + 2H 2 O ® H 3 AsO 4 + 2HI.

Arsenic reacts with halogens and sulfur. AsCl 3 chloride is a colorless oily liquid that fumes in air; hydrolyzed with water: AsCl 3 + 2H 2 O ® HAsO 2 + 3HCl. AsBr 3 bromide and AsI 3 iodide are known, which also decompose with water. In the reactions of arsenic with sulfur, sulfides of various compositions are formed - up to Ar 2 S 5. Arsenic sulfides dissolve in alkalis, in ammonium sulfide solution and in concentrated nitric acid, for example:

As 2 S 3 + 6KOH ® K 3 AsO 3 + K 3 AsS 3 + 3H 2 O,

2 S 3 + 3(NH 4) 2 S ® 2(NH 4) 3 AsS 3,

2 S 5 + 3(NH 4) 2 S ® 2(NH 4) 3 AsS 4,

As 2 S 5 + 40HNO 3 + 4H 2 O ® 6H 2 AsO 4 + 15H 2 SO 4 + 40NO.

In these reactions, thioarsenites and thioarsenates are formed - salts of the corresponding thioacids (similar to thiosulfuric acid).

In the reaction of arsenic with active metals, salt-like arsenides are formed, which are hydrolyzed by water. The reaction occurs especially quickly in an acidic environment with the formation of arsine: Ca 3 As 2 + 6HCl ® 3CaCl 2 + 2AsH 3 . Arsenides of low-active metals - GaAs, InAs, etc. have a diamond-like atomic lattice. Arsine is a colorless, odorless, highly poisonous gas, but impurities give it the smell of garlic. Arsine decomposes slowly into elements already at room temperature and quickly when heated.

Arsenic forms many organoarsenic compounds, for example, tetramethyldiarsine (CH 3) 2 As–As(CH 3) 2. Back in 1760, the director of the Serves porcelain factory, Louis Claude Cadet de Gassicourt, distilling potassium acetate with arsenic(III) oxide, unexpectedly received a fuming liquid containing arsenic with a disgusting odor, which was called alarsine, or Cadet's liquid. As it was later found out, this liquid contained the first obtained organic derivatives of arsenic: the so-called cacodyl oxide, which was formed as a result of the reaction

4CH 3 COOK + As 2 O 3 ® (CH 3) 2 As–O–As(CH 3) 2 + 2K 2 CO 3 + 2CO 2 , and dicacodyl (CH 3) 2 As–As(CH 3) 2 . Kakodyl (from the Greek “kakos” - bad) was one of the first radicals discovered in organic compounds.

In 1854, Parisian chemistry professor Auguste Kaur synthesized trimethylarsine by the action of methyl iodide on sodium arsenide: 3CH 3 I + AsNa 3 ® (CH 3) 3 As + 3NaI.

Subsequently, arsenic trichloride was used for syntheses, for example,

(CH 3) 2 Zn + 2AsCl 3 ® 2(CH 3) 3 As + 3ZnCl 2.

In 1882, aromatic arsines were obtained by the action of metallic sodium on a mixture of aryl halides and arsenic trichloride: 3C 6 H 5 Cl + AsCl 3 + 6Na ® (C 6 H 5) 3 As + 6NaCl. The chemistry of organic derivatives of arsenic developed most intensively in the 20s of the 20th century, when some of them had antimicrobial, as well as irritant and blister effects. Currently, tens of thousands of organoarsenic compounds have been synthesized.

Obtaining arsenic.

Arsenic is obtained mainly as a by-product of the processing of copper, lead, zinc and cobalt ores, as well as during gold mining. Some polymetallic ores contain up to 12% arsenic. When such ores are heated to 650–700° C in the absence of air, arsenic sublimes, and when heated in air, volatile oxide As 2 O 3 is formed - “white arsenic”. It is condensed and heated with coal, and arsenic is reduced. Producing arsenic is a harmful production. Previously, when the word “ecology” was known only to narrow specialists, “white arsenic” was released into the atmosphere, and it settled on neighboring fields and forests. The exhaust gases of arsenic plants contain from 20 to 250 mg/m 3 As 2 O 3, while usually the air contains approximately 0.00001 mg/m 3. The average daily permissible concentration of arsenic in the air is considered to be only 0.003 mg/m3. Paradoxically, even now it is not the factories that produce arsenic that pollute the environment much more heavily, but non-ferrous metallurgy enterprises and power plants that burn coal. Bottom sediments near copper smelters contain huge amounts of arsenic – up to 10 g/kg. Arsenic can also enter the soil with phosphorus fertilizers.

And another paradox: they receive more arsenic than is required; This is quite a rare case. In Sweden, “unnecessary” arsenic was even forced to be buried in reinforced concrete containers in deep abandoned mines.

The main industrial arsenic mineral is arsenopyrite FeAsS. There are large copper-arsenic deposits in Georgia, Central Asia and Kazakhstan, the USA, Sweden, Norway and Japan, arsenic-cobalt deposits in Canada, and arsenic-tin deposits in Bolivia and England. In addition, gold-arsenic deposits are known in the USA and France. Russia has numerous arsenic deposits in Yakutia, the Urals, Siberia, Transbaikalia and Chukotka.

Determination of arsenic.

A qualitative reaction to arsenic is the precipitation of yellow sulfide As 2 S 3 from hydrochloric acid solutions. Traces are determined by the March reaction or the Gutzeit method: strips of paper soaked in HgCl 2 darken in the presence of arsine, which reduces sublimate to mercury.

In recent decades, various sensitive analytical methods have been developed that can quantify minute concentrations of arsenic, for example in natural waters. These include flame atomic absorption spectrometry, atomic emission spectrometry, mass spectrometry, atomic fluorescence spectrometry, neutron activation analysis... If there is very little arsenic in the water, pre-concentration of the samples may be necessary. Using such concentration, a group of Kharkov scientists from the National Academy of Sciences of Ukraine developed in 1999 an extraction-X-ray fluorescence method for determining arsenic (as well as selenium) in drinking water with a sensitivity of up to 2.5–5 μg/l.

For the separate determination of As(III) and As(V) compounds, they are first separated from each other using well-known extraction and chromatographic methods, as well as using selective hydrogenation. Extraction is usually carried out using sodium dithiocarbamate or ammonium pyrrolidine dithiocarbamate. These compounds form water-insoluble complexes with As(III), which can be extracted with chloroform. The arsenic can then be converted back into the aqueous phase by oxidation with nitric acid. In the second sample, arsenate is converted to arsenite using a reducing agent, and then a similar extraction is performed. This is how “total arsenic” is determined, and then by subtracting the first result from the second, As(III) and As(V) are determined separately. If there are organic arsenic compounds in water, they are usually converted to methyldiodarsine CH 3 AsI 2 or dimethyliodarsine (CH 3) 2 AsI, which are determined by one or another chromatographic method. Thus, using high-performance liquid chromatography, nanogram quantities of a substance can be determined.

Many arsenic compounds can be analyzed using the so-called hydride method. It involves the selective reduction of the analyte into volatile arsine. Thus, inorganic arsenites are reduced to AsH 3 at pH 5 – 7, and at pH

The neutron activation method is also sensitive. It consists of irradiating a sample with neutrons, while 75 As nuclei capture neutrons and transform into the radionuclide 76 As, which is detected by characteristic radioactivity with a half-life of 26 hours. This way you can detect up to 10–10% arsenic in a sample, i.e. 1 mg per 1000 tons of substance

Use of arsenic.

About 97% of mined arsenic is used in the form of its compounds. Pure arsenic is rarely used. Only a few hundred tons of arsenic metal are produced and used annually throughout the world. In an amount of 3%, arsenic improves the quality of bearing alloys. Additions of arsenic to lead significantly increase its hardness, which is used in the production of lead batteries and cables. Small additions of arsenic increase corrosion resistance and improve the thermal properties of copper and brass. Highly purified arsenic is used in the production of semiconductor devices, in which it is alloyed with silicon or germanium. Arsenic is also used as a dopant, which gives “classical” semiconductors (Si, Ge) a certain type of conductivity.

Arsenic is also used as a valuable additive in non-ferrous metallurgy. Thus, the addition of 0.2...1% As to lead significantly increases its hardness. It has long been noticed that if a little arsenic is added to molten lead, then when casting shot, balls of the correct spherical shape are obtained. The addition of 0.15...0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gaseous environment. In addition, arsenic increases the fluidity of copper during casting and facilitates the process of wire drawing. Arsenic is added to some types of bronze, brass, babbitt, and printing alloys. And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately complicate the process in order to remove all arsenic from the metal. The presence of arsenic in ore makes production harmful. Harmful twice: firstly, for human health; secondly, for metals - significant arsenic impurities worsen the properties of almost all metals and alloys.

Various arsenic compounds, which are produced annually in tens of thousands of tons, are more widely used. As 2 O 3 oxide is used in glass making as a glass brightener. Even the ancient glassmakers knew that white arsenic makes glass “dull”, i.e. opaque. However, small additions of this substance, on the contrary, lighten the glass. Arsenic is still included in the formulations of some glasses, for example, “Vienna” glass for thermometers.

Arsenic compounds are used as an antiseptic to protect against spoilage and preserve skins, furs and stuffed animals, to impregnate wood, and as a component of antifouling paints for the bottoms of ships. For this purpose, salts of arsenic and arsenous acids are used: Na 2 HAsO 4, PbHAsO 4, Ca 3 (AsO 3) 2, etc. The biological activity of arsenic derivatives has interested veterinarians, agronomists, and sanitary and epidemiological service specialists. As a result, arsenic-containing stimulants for the growth and productivity of livestock, anthelmintic agents, and medicines for the prevention of diseases in young animals on livestock farms appeared. Arsenic compounds (As 2 O 3, Ca 3 As 2, Na 3 As, Parisian green) are used to control insects, rodents, and weeds. Previously, such uses were widespread, especially in fruit trees, tobacco and cotton plantations, for ridding livestock of lice and fleas, for promoting growth in poultry and pig production, and for drying cotton before harvest. Even in ancient China, rice crops were treated with arsenic oxide to protect them from rats and fungal diseases and thus increase the yield. And in South Vietnam, American troops used cacodylic acid (Agent Blue) as a defoliant. Now, due to the toxicity of arsenic compounds, their use in agriculture is limited.

Important areas of application of arsenic compounds are the production of semiconductor materials and microcircuits, fiber optics, growing single crystals for lasers, and film electronics. Arsine gas is used to introduce small, strictly dosed amounts of this element into semiconductors. Gallium arsenides GaAs and indium InAs are used in the manufacture of diodes, transistors, and lasers.

Arsenic also finds limited use in medicine. . Arsenic isotopes 72 As, 74 As and 76 As with half-lives convenient for research (26 hours, 17.8 days and 26.3 hours, respectively) are used to diagnose various diseases.

Ilya Leenson

Arsenic is a non-metal and forms compounds similar in its chemical properties. However, along with non-metallic properties, arsenic also exhibits metallic ones. In air under normal conditions, arsenic is slightly oxidized from the surface. Arsenic and its analogues are insoluble neither in water nor in organic solvents.

Arsenic is chemically active. In air at normal temperatures, even compact (fused) metallic arsenic is easily oxidized; when heated, powdered arsenic ignites and burns with a blue flame to form As 2 O 3 oxide. Thermally less stable non-volatile oxide As 2 O 5 is also known.

When heated (in the absence of air), As sublimes (sublimation temperature 615 o C). The steam consists of As 4 molecules with an insignificant (about 0.03%) admixture of As 2 molecules.

Arsenic belongs to the group of oxidizing-reducing elements. When exposed to strong reducing agents, it exhibits oxidizing properties. Thus, under the action of metals and hydrogen at the moment of release, it is capable of producing the corresponding metal and hydrogen compounds:

6Ca +As 4 = 2Ca 3 As 2

Under the influence of strong oxidizing agents, arsenic transforms into a tri- or pentavalent state. For example, when heated in air, arsenic, oxidized by oxygen, burns and forms white smoke - arsenic (III) oxide As 2 O 3:

As 4 + 3O 2 =2As 2 O 3

Stable forms of arsenic oxide in the gas phase are sesquioxide (arsenic anhydride) As 2 O 3 and its dimer As 4 O 6. Up to 300 o C, the main form in the gas phase is a dimer; above this temperature it is noticeably dissociated, and at temperatures above 1800 o C the gaseous oxide consists practically of monomeric As 2 O 3 molecules.

A gaseous mixture of As 4 O 6 and As 2 O 3 is formed during the combustion of As in oxygen, during the oxidative roasting of As sulfide minerals, such as arsenopyrite, non-ferrous metal ores and polymer ores.

When As 2 O 3 (As 4 O 6) vapor condenses above 310 o C, the glassy form of As 2 O 3 is formed. When steam condenses below 310 o C, a colorless polycrystalline cubic modification of arsenolite is formed. All forms of As 2 O 3 are highly soluble in acids and alkalis.

As(V) oxide (arsenic anhydride) As 2 O 5 – colorless crystals of the orthorhombic system. When heated, As 2 O 5 dissociates into As 4 O 6 (gas) and O 2 . As 2 O 5 is obtained by dehydrating concentrated solutions of H 3 AsO 4 followed by calcination of the resulting hydrates.

The oxide As 2 O 4 is known, obtained by sintering As 2 O 3 and As 2 O 5 at 280 o C in the presence of water vapor. Gaseous AsO monoxide is also known, which is formed during an electrical discharge in As trioxide vapor at reduced pressure.

When dissolved in water, As 2 O 5 forms orthoarsenic H 3 AsO 3 , or As(OH) 3 , and metaarsenic HAsO 2 , or AsO(OH), which exist only in solution and have amphoteric, predominantly acidic, properties.

In relation to acids, arsenic behaves as follows:

— arsenic does not react with hydrochloric acid, but in the presence of oxygen arsenic trichloride AsCl 3 is formed:

4As +3O 2 +12HCl = 4AsCl 3 +6H 2 O

- dilute nitric acid, when heated, oxidizes arsenic to orthoarsenic acid H 3 AsO 3 , and concentrated nitric acid – to orthoarsenic acid H 3 AsO 4:

3As + 5HNO 3 + 2H 2 O = 3H 2 AsO 4 +5NO

Orthoarsenic acid(arsenic acid) H 3 AsO 4 *0.5H 2 O – colorless crystals; melting point – 36 o C (with decomposition); soluble in water (88% by weight at 20 o C); hygroscopic; in aqueous solutions – tribasic acid; when heated to about 100 o C, it loses water, turning into pyroarsenic acid H 4 As 5 O 7, at higher temperatures it turns into metaarsenic acid HAsO 3. Obtained by oxidation of As or As 2 O 3 with concentrated HNO 3 . It is easily soluble in water and is approximately equal in strength to phosphorus.

The oxidizing properties of arsenic acid are noticeable only in an acidic environment. Arsenic acid is capable of oxidizing HI to I 2 by reversible reactions:

H 3 AsO 4 + 2HI = H 3 AsO 3 + I 2 + H 2 O

Orthoarsenic acid (arsenous acid) H 3 AsO 3 exists only in aqueous solution; weak acid; obtained by dissolving As 2 O 3 in water; intermediate product in the preparation of arsenites (III) and other compounds.

- concentrated sulfuric acid reacts with arsenic according to the following equation to form orthoarsenic acids:

2As + 3H 2 SO 4 = 2H 3 AsO 3 +3SO 2

- alkali solutions do not react with arsenic in the absence of oxygen. When arsenic is boiled with alkalis, it is oxidized into the arsenic acid salt H 3 AsO 3 . When fused with alkalis, arsine (arsenous hydrogen) AsH 3 and arsenates (III) are formed. Apply AsH 3

for doping semiconductor materials with arsenic to obtain high purity As.

Unstable higher arsines are known: diarsine As 2 H 4, decomposes already at -100 o C; triarsine As 3 H 5 .

Metallic arsenic easily reacts with halogens, giving volatile halides AsHal 3:

As +3Cl 2 = 2AsCl 3

AsCl 3 is a colorless oily liquid that fumes in air and, when solidified, forms crystals with a pearlescent sheen.

C F 2 also forms AsF 5 - pentafluoride - a colorless gas, soluble in water and alkali solutions (with a small amount of heat), in diethyl ether, ethanol and benzene.

Powdered arsenic spontaneously ignites in an environment of F 2 and Cl 2 .

With S, Se and Te, arsenic forms the corresponding chalcogenides:

sulfides - As 2 S 5, As 2 S 3 (orpiment mineral in nature), As 4 S 4 (realgar mineral) and As 4 S 3 (dimorphite mineral); selenides – As 2 Se 3 and As 4 Se 4; telluride – As 2 Te 3 . Arsenic chalcogenides are stable in air, insoluble in water, highly soluble in alkali solutions, and when heated - in HNO 3. They have semiconductor properties and are transparent in the IR region of the spectrum.

With most metals it gives metallic compounds - arsenides. Gallium arsenide and indium arsenide– important semiconductor compounds.

There are numerous known arsenicorganic connections. Organoarsenic compounds contain an As-C bond. Sometimes organoarsenic compounds include all organic compounds containing As, for example, esters of arsenic acid (RO) 3 As and arsenic acid (RO) 3 AsO. The most numerous group of organoarsenic compounds are As derivatives with a coordination number of 3. This includes organoarsines R n AsH 3-n, tetraorganodiarsines R 2 As-AsR 2, cyclic and linear polyarganoarsines (RAs) n, as well as organoarsonic and diarganoarsinous acids and their derivatives R n AsX 3-n (X= OH, SH, Hal, OR', NR 2', etc.). Most organoarsenic compounds are liquids, polyorganoarsines and organic acids As are solids, CH 3 AsH 2 and CF 3 AsH 2 are gases. These compounds, as a rule, are soluble in organic solvents, limitedly soluble in water, and relatively stable in the absence of oxygen and moisture. Some tetraorganodiarsines are flammable in air.

True, empirical, or gross formula: As

Molecular weight: 74.922

Arsenic- (lat. Arsenicum; designated by the symbol As) - chemical element of the 15th group (according to the outdated classification - the main subgroup of the fifth group) of the fourth period of the periodic system; has atomic number 33. The simple substance is a brittle, steel-colored semimetal with a greenish tint (in the gray allotropic modification). CAS number: 7440-38-2.

Story

Arsenic is one of the oldest elements used by humans. Arsenic sulfides As 2 S 3 and As 4 S 4, the so-called orpiment (“arsenic”) and realgar, were familiar to the Romans and Greeks. These substances are poisonous. Arsenic is one of the elements found in nature in free form. It can be isolated relatively easily from compounds. Therefore, history does not know who first obtained elemental arsenic in a free state. Many attribute the role of discoverer to the alchemist Albertus Magnus. The works of Paracelsus also describe the production of arsenic as a result of the reaction of arsenic with eggshells. Many historians of science suggest that arsenic metal was obtained much earlier, but it was considered a representative of native mercury. This can be explained by the fact that arsenic sulfide was very similar to the mercury mineral. And the release from it was very easy, as with the release of mercury. Elemental arsenic has been known in Europe and Asia since the Middle Ages. The Chinese obtained it from ores. Unlike the Europeans, they could diagnose death from arsenic poisoning. But this method of analysis has not reached the present time. Europeans learned to determine the onset of death from arsenic poisoning much later; this was first done by D. Marchais. This reaction is still used today.
Arsenic is sometimes found in tin ores. Chinese literature of the Middle Ages describes cases of death of people who drank water or wine from tin vessels due to the presence of arsenic in it. For a relatively long time, people confused arsenic itself and its oxide and mistook it for one substance. This misunderstanding was eliminated by G. Brandt and A. Lavoisier, who proved that these are different substances and that arsenic is an independent chemical element. Arsenic oxide has long been used to kill rodents. Hence the origin of the Russian name of the element. It comes from the words "mouse" and "poison".

Etymology

The name of arsenic in Russian comes from the word “mouse”, in connection with the use of its compounds to exterminate mice and rats. The Greek name ἀρσενικόν comes from the Persian زرنيخ (zarnik) - “yellow orpiment.” Folk etymology dates back to ancient Greek. ἀρσενικός - male.
The Latin name arsenicum is a direct borrowing of the Greek ἀρσενικόν. In 1789, A. Lavoisier included arsenic in the list of chemical elements called arsenic.

Being in nature

Arsenic is a trace element. The content in the earth's crust is 1.7·10−4% by mass. In sea water 0.003 mg/l. This element is sometimes found in nature in its native form; the mineral has the appearance of metallic shiny gray shells or dense masses consisting of small grains.
About 200 arsenic-containing minerals are known. In small concentrations it often accompanies lead, copper and silver ores. Two natural arsenic minerals in the form of sulfides (binary compounds with sulfur) are quite common: orange-red transparent realgar AsS and lemon-yellow orpiment As 2 S 3. A mineral of industrial importance for the production of arsenic is arsenopyrite (arsenic pyrite) FeAsS or FeS 2 FeAs 2 (46% As), arsenic pyrite is also processed - löllingite (FeAs 2) (72.8% As), scorodite FeAsO 4 (27 - 36% As). Most of the arsenic is mined as a by-product during the processing of arsenic-containing gold, lead-zinc, copper pyrite and other ores.

Place of Birth

The main industrial arsenic mineral is arsenopyrite FeAsS. There are large copper-arsenic deposits in Georgia, Central Asia and Kazakhstan, the USA, Sweden, Norway and Japan, arsenic-cobalt deposits in Canada, and arsenic-tin deposits in Bolivia and England. In addition, gold-arsenic deposits are known in the USA and France. Russia has numerous arsenic deposits in Yakutia, the Urals, Siberia, Transbaikalia and Chukotka.

Isotopes

33 isotopes and at least 10 excited states of nuclear isomers are known. Of these isotopes, only 75 As is stable and natural arsenic consists only of this isotope. The longest-lived radioactive isotope 73 As has a half-life of 80.3 days.

Receipt

The discovery of a method for producing metallic arsenic (gray arsenic) is attributed to the medieval alchemist Albertus Magnus, who lived in the 13th century. However, much earlier, Greek and Arab alchemists were able to obtain arsenic in free form by heating “white arsenic” (arsenic trioxide) with various organic substances.
There are many ways to obtain arsenic: by sublimation of natural arsenic, by the thermal decomposition of arsenic pyrite, by the reduction of arsenous anhydride, etc. Currently, to obtain metallic arsenic, arsenopyrite is most often heated in muffle furnaces without access to air. At the same time, arsenic is released, the vapors of which condense and turn into solid arsenic in iron tubes coming from the furnaces and in special ceramic receivers. The residue in the furnaces is then heated with access to air, and then the arsenic is oxidized into As 2 O 3. Metallic arsenic is obtained in rather small quantities, and the main part of arsenic-containing ores is processed into white arsenic, that is, into arsenic trioxide - arsenic anhydride As 2 O 3. The main method of production is roasting sulfide ores followed by reduction of the oxide with coal

Application

Arsenic is used to alloy lead alloys used to prepare shot, since when shot is cast using the tower method, drops of the arsenic-lead alloy acquire a strictly spherical shape, and in addition, the strength and hardness of lead increases significantly.
Arsenic of special purity (99.9999%) is used for the synthesis of a number of useful and important semiconductor materials - arsenides (for example, gallium arsenide) and other semiconductor materials with a crystal lattice such as zinc blende.
Arsenic sulfide compounds - orpiment and realgar - are used in painting as paints and in the leather industry as means for removing hair from the skin.
In pyrotechnics, realgar is used to produce “Greek” or “Indian” fire, which occurs when a mixture of realgar with sulfur and nitrate burns (when burned, it forms a bright white flame).
Some organoelement compounds of arsenic are chemical warfare agents, for example, lewisite.
At the beginning of the 20th century, some cacodyl derivatives, for example, salvarsan, were used to treat syphilis; over time, these drugs were displaced from medical use for the treatment of syphilis by other, less toxic and more effective, pharmaceutical drugs that do not contain arsenic.
Many of the arsenic compounds in very small doses are used as drugs to combat anemia and a number of other serious diseases, as they have a clinically noticeable stimulating effect on a number of specific functions of the body, in particular, on hematopoiesis. Of the inorganic arsenic compounds, arsenous anhydride can be used in medicine for the preparation of pills and in dental practice in the form of a paste as a necrotizing drug. This drug was colloquially and colloquially called “arsenic” and was used in dentistry for local necrosis of the dental nerve (see pulpitis). Currently (2015), arsenic preparations are rarely used in dental practice due to their toxicity. Now other methods of painless necrosis of the tooth nerve under local anesthesia have been developed and are being used.

Biological role and physiological effect

Arsenic and all its compounds are poisonous. In acute arsenic poisoning, vomiting, abdominal pain, diarrhea, and depression of the central nervous system are observed. The similarity of the symptoms of arsenic poisoning with the symptoms of cholera for a long time made it possible to mask the use of arsenic compounds (most often arsenic trioxide, the so-called “white arsenic”) as a deadly poison. In France, arsenic trioxide powder received the common name “hereditary powder” (French poudre de succession) for its high efficiency. There is an assumption that Napoleon was poisoned with arsenic compounds on the island of St. Helena. In 1832, a reliable qualitative reaction to arsenic appeared - the Marsh test, which significantly increased the efficiency of diagnosing poisoning. In areas where there is an excess of arsenic in the soil and water, it accumulates in the thyroid gland in people and causes endemic goiter. Help and antidotes for arsenic poisoning: taking aqueous solutions of sodium thiosulfate Na 2 S 2 O 3, gastric lavage, taking milk and cottage cheese; a specific antidote is unithiol. The maximum permissible concentration in the air for arsenic is 0.5 mg/m³. Work with arsenic in sealed boxes using protective clothing. Due to their high toxicity, arsenic compounds were used as poisonous agents in the First World War. In Western countries, arsenic was known primarily as a strong poison, but in traditional Chinese medicine it was used for almost two thousand years to treat syphilis and psoriasis. Now doctors have proven that arsenic has a positive effect in the fight against leukemia. Chinese scientists have discovered that arsenic attacks proteins that are responsible for the growth of cancer cells. Arsenic in small doses is carcinogenic, its use as a medicine that “improves the blood” (the so-called “white arsenic”, for example, “Blo arsenic tablets”, etc.) continued until the mid-1950s, and contributed significantly contribution to the development of cancer. Organic arsenic compounds are traditionally used to treat sleeping sickness. Recently, a man-made environmental disaster in southern India received wide publicity - due to excessive water withdrawal from aquifers, arsenic began to leak into drinking water. This caused toxicity and cancer in tens of thousands of people. It was believed that “microdoses of arsenic, introduced with caution into a growing organism, promote the growth of human and animal bones in length and thickness; in some cases, bone growth can be caused by microdoses of arsenic during the period of termination of growth.” It was also believed that “With prolonged consumption of small doses of arsenic, the body develops immunity: This fact has been established for both people and animals. There are cases where habitual consumers of arsenic immediately took doses several times higher than the lethal dose and remained healthy. Experiments on animals have shown the uniqueness of this habit. It turned out that an animal accustomed to arsenic by consuming it quickly dies if a significantly smaller dose is injected into the blood or under the skin.” However, such “addiction” is very limited in nature, in relation to the so-called. “acute toxicity” and does not protect against neoplasms. However, the effects of microdoses of arsenic-containing drugs as an anticancer agent are currently being investigated. Extremophilic bacteria are known that are able to survive at high concentrations of arsenate in the environment. It was suggested that in the case of the GFAJ-1 strain, arsenic replaces phosphorus in biochemical reactions, in particular, it is part of DNA, but this assumption was not confirmed.

In forensic medicine

The method for postmortem detection of arsenic in cases of suspected poisoning was developed at the beginning of the 19th century. English chemist James Marsh.

Arsenic contamination

On the territory of the Russian Federation in the city of Skopin, Ryazan region, as a result of many years of work of the local metallurgical plant SMK Metallurg, about one and a half thousand tons of dusty waste with a high content of arsenic were buried in the burial grounds of the enterprise. Arsenic is a common element in many gold deposits, leading to additional environmental problems in gold-mining countries such as Romania.

Arsenicum or arsenic is the name in Latin for arsenic in chemical tables. In Russian, the word arsenic appeared after the oxide of this substance was used in the fight against mice and rats. Arsenic has the appearance of very small shells with a metallic sheen or a dense formation of small grains. One of its inorganic compounds, arsenic anhydride, is widely used in medical, particularly dental practice.

How and why does a dentist use arsenic?

This substance is used by doctors to obtain an analgesic effect. A drug with arsenic kills the nerve of a diseased tooth; of course, there are other means to obtain the same effect, but this method is still continued to be used because it is effective and has been proven for decades.

Under the layer of tooth enamel and dentin (the hard tissue of the tooth), which forms its basis, is the pulp. It consists of many nerve endings and blood vessels. In acute pulpitis, inflammation and swelling occur, which compresses the nerve endings, resulting in severe pain.

On a note! Tooth enamel is the strongest biological tissue; drill bits are therefore made using diamond.

Arsenic provides:

• necrotic effect on all nerve endings in the tooth;
• pulp necrosis;
• cessation of blood supply;
• cessation of impulses from nerve endings.

Arsenic paste contains an anesthetic, so the process of exposure to arsenic is painless.

The composition of the paste may vary depending on the manufacturer. The approximate composition of the drug is as follows:

• arsenic anhydride;
• novocaine, lidocaine or other anesthetic;
• antiseptic such as camphor;
• tannin, a viscous substance that prolongs the action of arsenic.

If severe pain is a concern, an additional anesthetic may be applied over the paste.

The doctor drills the tooth, cleans it and introduces the drug into the tooth cavity. Then it is closed with a temporary filling, which the patient wears depending on the doctor’s instructions. This can range from 1 to 5 days.

On a note! The penetration of arsenic from the tooth cavity into the oral cavity should be excluded, as this can lead to osteomyelitis.

During the action of arsenic, the nerves inside the tooth can influence the occurrence of aching pain, this can last for several hours; bromide is taken for pain relief. After the allotted time, the doctor will remove the temporary filling, remove the arsenic, the destroyed nerve and seal the prepared tooth cavity.

Effect of arsenic

In tissues where arsenous anhydride acts, disruption of normal cell respiration may occur. Even a small amount of the drug affects the dilation of blood vessels and can lead to hemorrhages. Most of the components decompose in the nerve fibers. Such changes are directly proportional to the dosage of the substance and the duration of its effect. The drug with arsenic is used when there is a need to remove nerves and pulp.

On a note! It is absolutely prohibited to drink alcohol after adding arsenic paste, as its effects are enhanced and the risk of intoxication becomes very likely.

Indications and contraindications

The substance is widely used by public clinics as an effective and most affordable means of necrosis of the dental nerve. The drug is also used for:

• inability to perform another type of anesthesia;
• the need for emergency killing of the nerve;
• allergies to other painkillers;
• ineffectiveness of other painkillers;
• availability of individual indications;
• in pediatric dentistry only with formed roots.

Arsenic paste is not used in the following cases:

• children up to one and a half years old;
• allergic reaction to the drug;
• pregnancy;
• diseases of the urinary organs;
• threats of glaucoma;
• breastfeeding;
• inability to completely clean the canal;
• curvature of the dental canal;
• violation of the integrity of the roots of the teeth.

On a note! Traces of certain metals in the body, including arsenic, may play a role in the pathogenesis of glaucoma.

If a tooth hurts with arsenic

If toothache continues for more than a day, you should immediately consult a dentist. A similar reaction may occur in the following cases:

• allergies to arsenic or other components;
• the doctor put arsenic on the closed pulp;
• inflammation or necrosis of tissue around the tooth;
• low concentration of the substance;
• presence of periodontitis;
• violations in the technology of applying substances;
• high sensitivity, in which the pain may subside after a few days.

If the pain is severe, especially at night, it is better to seek help. When the tissue around the tooth becomes inflamed or necrosis caused by arsenic, very dangerous conditions can occur that affect the periosteum or jaw bones.

On a note! On the first day after adding arsenic, you can take a tablet of any painkiller for pain.

If arsenic fell

There are situations when, during a meal, a temporary filling is destroyed and arsenic falls out. Immediately after this, you need to rinse your mouth with a soda solution with added iodine, this is done to neutralize possible remnants of the anesthetic paste. Then the tooth cavity must be closed with a cotton ball and consult a dentist.

In other situations, arsenic may be accidentally ingested, but the dosage of the drug is such that it will not cause negative consequences in the form of intoxication. To not worry about this, you can drink milk or take activated charcoal. A filling with arsenic can fall out if the doctor’s recommendations are not followed, these include:

1. Do not eat for two hours after visiting the doctor.
2. If a sour taste appears on the filling, rinse with a soda solution.
3. Try not to chew on the side of the affected tooth or eat soft foods.
4. Be sure to visit a doctor within the specified period to remove arsenic, temporary filling and continue treatment.

On a note! If the time spent by arsenic in the tooth cavity is exceeded, necrosis of the tissue around the tooth may develop; in patients with diseases of the digestive system and hypersensitivity to the drug, intoxication may develop.

Video - Specialist about arsenic in teeth

Getting rid of arsenic on your own

You can get rid of the paste yourself, but it is not advisable. This should only be done in extreme cases when help is needed, but for some reason it cannot be obtained in a timely manner.

If you need to remove a temporary filling, this can be done using a syringe needle or any other. Arsenic is removed with its help; the needle must first be treated with alcohol. After this, rinse the mouth several times a day with a solution of soda with a few drops of iodine. Be sure to cover the exposed tooth with a piece of cotton wool and contact a dentist as soon as possible.

Consequences of exceeding the dose of arsenic

If the dose was exceeded by the doctor or the patient overextended it and did not show up on time to remove the arsenic, then negative consequences are possible, the most common of which are:

• pulp swelling;
• darkening of hard tooth tissue;
• periodontitis;
• osteonecrosis;
• general intoxication.

Considering all the consequences, arsenic-based preparations are not used for pregnant and lactating women, and arsenic is practically not used for the treatment of children's teeth.

On a note! In the case of treating children, it is difficult to calculate the required dose of arsenic paste, and the child can independently pick out the filling and swallow arsenic.

Comparison of arsenic and arsenic-free pastes

Pastes with arsenic	Peculiarities
	30% arsenic anhydride content. It is used when the carious process spreads through thin tooth tissue, when the pulp is infected. The maximum period for leaving the paste in the tooth is 3 days.
	The maximum period for leaving the paste in the tooth is 7 days. In addition to the active substance, it consists of lidocaine, camphor, ephedrine, and chlorophenol. It is not recommended for use by athletes; it may show a positive reaction during anti-doping control.
Formaldehyde-based pastes	Such pastes, unlike arsenic pastes, can mummify the pulp, but are still considered less effective
	Contains paraformaldehyde, lidocaine, creosote. Validity time from 2 to 7 days
	Contains paraform, chlorophenol, menthol, camphor, lidocaine is used on baby teeth, allows you not to remove the pulp
	Contains lidocaine, paraformaldehyde, phenol. Apply from 7 to 10 days

At the dental clinic, the doctor will use an anesthetic according to individual indications and will not administer arsenic without your consent.