How is arsenic made
Information on the element: arsenic
International name (IUPAC): Arsenic
Origin: Arsenic is the chemical element with the atomic number 33. In the periodic table of the elements it can be found under the symbol As in the 5th main group, the nitrogen group. Arsenic is seldom native, mostly in the form of sulphides. It belongs to the semimetals because, depending on the modification, it shows metallic or non-metallic properties.
Arsenic compounds have been known since ancient times. Although they are highly toxic, they are used as part of individual medicines. Arsenic is also used for doping semiconductors and as a component of III-V semiconductors such as gallium arsenide.
The name arsenic comes directly from the Greek arsenikón back, the name of the arsenic mineral auripigment. It can already be found in Dioscorides in the 1st century. The Greek name for its part seems to have its origin in Middle Persian al-zarnik (gold-colored) and probably got into Greek through Semitic mediation. In terms of folk etymology, the name was erroneously derived from the Greek word arsenikós, which translates as masculine / strong. The name arsenic has only been in use since the 19th century. The element symbol was proposed by Jöns Jakob Berzelius in 1814.
The first contact of humans with arsenic can be traced back to the 3rd millennium BC. - In the hair of the mummy of an alpine inhabitant popularly known as Ötzi, which was preserved in the glacier ice, large amounts of arsenic could be detected, which is archaeologically interpreted as an indication that the man concerned was active in copper processing - copper ores are often contaminated with arsenic.
In classical antiquity, arsenic was auripigment in the form of the arsenic sulfide (As2S.3) and Realgar (As4S.4), which were described by the Greek Theophrastus, the successor of Aristotle. The Greek philosopher Democritus also had in the 2nd century BC Proven knowledge of arsenic compounds. The Leiden papyrus from the 3rd century AD suggests that they were used to color silver gold-like and copper white. The Roman emperor Caligula supposedly commissioned a project for the production of gold from the (golden yellow) auripigment as early as the 1st century AD. The alchemists, who knew arsenic compounds verifiably as they were mentioned in the ancient standard work Physica et Mystica, suspected a relationship with sulfur and mercury. Arsenic (III) sulfide was used as a painter's paint and depilatory as well as for the external and internal treatment of lung diseases.
In the Middle Ages, arsenic (arsenic (III) oxide) was found in smelter smoke (dust-laden exhaust gas from metallurgical furnaces). Albertus Magnus first described the production of arsenic by reducing arsenic with coal around 1250. He is therefore traditionally considered the discoverer of the element, even if there are indications that the elementary metal was made earlier. Paracelsus introduced it to medicine in the 16th century. Around the same time, arsenic preparations were also described in the Chinese encyclopedia Pen-ts' ao Kan-mu by the pharmacist Li Shi-zhen; the author particularly emphasizes its use as a pesticide in rice fields. In the 17th century, the yellow aura pigment became popular with Dutch painters as the royal yellow; However, modern restorers are challenged by the fact that the pigment transforms into arsenic (III) oxide over long periods of time and crumbles from the canvas. From 1740 on, arsenic preparations were used successfully in Europe as a dressing agent in crop protection; however, this use was banned again in 1808 because of its high toxicity. Applications in lead casting, in particular for bullets, followed. Despite the inglorious importance of arsenic as a murderous poison, arsenic was one of the most important asthma drugs in the early 19th century. It appears to be based on reports that the Chinese were said to smoke arsenic in combination with tobacco to get lungs that were as strong as bellows. At that time, in the form of copper arsenates, it was also used in dyes such as Parisian green, which were used to print wallpaper. When the humidity was high, these pigments were converted into toxic, volatile arsenic compounds by mold infestation, which often led to chronic arsenic poisoning. The premature death of the French Emperor Napoléon Bonaparte in exile on St. Helena is probably not due to poisoning with the arsenic released from the wallpaper, but rather to stomach cancer. In the 1950s, at the height of the Cold War, the American ambassador, Clare Booth Luce, fell ill in Rome for the same reason - the fact that the disease could be traced back to the mold-infested wallpaper and not to enemy secret agents contributed to this Contribute not only to the ambassador's recovery, but also to keeping the peace. In 1900, mass poisoning occurred in Manchester, UK, affecting several thousand people. As it turned out, everyone had been drinking beer from the same brewery. In the preliminary stages of beer production, sulfuric acid appears to have been used, which in turn was produced from sulfur obtained from sulphide minerals contaminated with arsenopyrite. About 70 people died from poisoning. But arsenic was also used in wars: In the First World War, arsenic compounds were used in chemical warfare agents such as blue cross or lewisite; in the affected victims they caused excruciating pain and severe physical damage by attacking the skin and lungs.
Importance: arsenikón = mineral name / gold-colored / masculine-strong
Group: 15 (V A)
Group name: Nitrogen group
Oxidation number: 3 (5, -3)
Atomic mass [u]: 72,64
Electronegativity (according to Allred): 2,2
Electronegativity (according to Pauling): 2,18
Physical state (20 ° C): firmly
Density [g / cm2]: 5,323
Melting temperature [° C]: 817 (at 27.5 bar)
Boiling temperature [° C]: 614
Crystal structure: rhombohedral
- Properties: Together with nitrogen, phosphorus, antimony and bismuth, arsenic forms the 5th main group of the periodic table. Because of its physical and chemical properties, it occupies a middle place in this element group. Arsenic has a relative atomic mass of 74.92159. The radius of the arsenic atom is 124.5 picometers. When covalently bound, it is slightly smaller (121 picometers). Due to the release of the external electrons (valence electrons) during ionization, the radius is reduced considerably to 34 picometers (As5+; the outermost p and s orbital remains unoccupied) and 58 picometers (As3+; only the p orbital is unoccupied). In chemical complex compounds this is As5+-Cation of four binding partners (ligands), As3+ surrounded by six. However, arsenic occurs only very rarely in a clearly ionic form.
According to Pauling, the value for electronegativity is 2.18 on a scale from 0 (metals) to 4 (non-metal) and is thus comparable with the value of the group neighbor phosphorus. The semi-metal character of arsenic is also shown by the fact that the required dissociation energy of 302.7 kJ / mol, i.e. the energy that has to be applied to dissolve a single arsenic atom from an arsenic solid, is between that of the non-metal nitrogen (473.02 kJ / mol; covalent bond) and the metal bismuth (207.2 kJ / mol; metallic bond). Under normal pressure, arsenic sublimes at a temperature of 616 ° C, i.e. it changes from the solid state of aggregation directly into the gas phase. Arsenic vapor is lemon yellow and is composed of As up to around 800 ° C4Molecules together. As are above 1700 ° C2Molecules.
Depending on the connection partner, arsenic shows oxidation states between -3 and +5. It forms compounds with electropositive elements such as hydrogen or metals in which it has an oxidation state of -3. Examples are monoarsan (AsH3) and arsenic copper (Cu3As). In compounds with electronegative elements such as the non-metals oxygen, sulfur and chlorine, it has the +3 or +5 oxidation state; The former tends to be preferred over the elements nitrogen and phosphorus, which are in the same main group.
- Modifications: Like other elements of the nitrogen group, arsenic occurs in various allotropic modifications. In contrast to nitrogen, which occurs in the form of diatomic molecules with a covalent triple bond, the corresponding As2-Molecules unstable; Instead, arsenic forms covalent networks.
- : Gray or metallic arsenic is the most stable form. It has a density of 5720 kg / m3. Its crystals are steel gray, have a metallic sheen and conduct electricity.
If you look at the structural structure of the gray arsenic, you can see layers of corrugated six-membered arsenic, which assume the so-called chair conformation. The arsenic atoms in it form a double layer if you look at the structure of the layer in cross section. The superposition of these double layers is very compact. Certain atoms of the next layer above or below are almost as far away from a reference atom as within the double layer under consideration. This structure means that the gray arsenic modification, like the homologous elements antimony and bismuth, is very brittle. This is why these three elements are often referred to as brittle metals.
- : Becomes arsenic vapor, in which arsenic is usually called As4-Tetrahedron is present, cooled quickly, the metastable yellow arsenic forms with a density of 1970 kg / m3. It also consists of tetrahedral As4Molecules. Yellow arsenic is a non-metal and as a result does not conduct electricity. It crystallizes from carbon disulfide and forms cubic, highly refractive crystals that smell of garlic. At room temperature and particularly quickly when exposed to light, yellow arsenic converts into gray arsenic.
- : Black arsenic itself can occur in two different modifications. Amorphous black arsenic is created by cooling arsenic vapor on surfaces with a temperature of 100 to 200 ° C. It does not have an ordered structure, but is in an amorphous, glass-like form, analogous to red phosphorus. The density is 4700 to 5100 kg / m3. Above 270 ° C, the black arsenic changes into the gray modification. If vitreous, amorphous black arsenic is heated to 100 to 175 ° C in the presence of metallic mercury, the metastable orthorhombic black arsenic is formed, which is comparable to black phosphorus.
- : The reduction of arsenic compounds in aqueous solution results in copolymers similar to phosphorus. In these, a part of the free valences of the arsenic binds hydroxyl groups (-OH). This form of arsenic is called brown arsenic.
- : Gray or metallic arsenic is the most stable form. It has a density of 5720 kg / m3. Its crystals are steel gray, have a metallic sheen and conduct electricity.
- Use: Arsenic is added to lead alloys to improve their strength and make the lead castable. Especially the finely structured plates of accumulators could not be cast without arsenic.
Historically, arsenic was an important ingredient in copper alloys, which made it easier to process.
In the past, metallic arsenic was occasionally used to create matt gray surfaces on metal parts in order to simulate aging.
In electronics, it is at least 99.9999 percent pure element for gallium arsenide semiconductors, so-called III-V semiconductors (due to the combination of elements from the 3rd and 5th main group of the periodic table), as well as for epitaxial layers on wafers in the form of indium arsenide phosphide and gallium arsenide phosphide play an essential role in the production of high-frequency components such as integrated circuits (ICs), light-emitting diodes (LEDs) and laser diodes (LDs). At the beginning of 2004 there were only three manufacturers of high-purity arsenic worldwide, two in Germany and one in Japan.
In the form of its compounds, arsenic is used in some countries as a pesticide in viticulture, as a fungicide (antifungal agent) in the timber industry, as a wood preservative, as a rat poison and as a discoloration agent in glass production. Its use is very controversial because the arsenic compounds used (mainly arsenic (III) oxide) are highly toxic.
- Arsenic in medicines: The use of arsenic-containing minerals as a remedy has already been attested by the authors of antiquity, Hippocrates and Pliny. They were used as an anti-fever agent, as a tonic and for the treatment of migraines, rheumatism, malaria, tuberculosis and diabetes. In the 18th century, a mixture of potassium arsenite and lavender water became known as Fowler's solution, which was long considered a medicinal miracle cure and was used as an antipyretic, medicinal water and even as an aphrodisiac. Potassium arsenite was used as a component of Fowler's solution until the 1960s in Germany as a treatment for psoriasis.
Medicines containing arsenic experienced an upswing at the beginning of the 20th century. In 1905, Harold Wolferstan Thomas and Anton Breinl were able to observe that the arsenic-containing preparation atoxyl kills trypanosomes, the pathogen causing sleeping sickness. In 1920 a further development, tryparsamide, was used in tropical Africa from 1922 to 1970 for the treatment of sleeping sickness. It was the cornerstone in containing this epidemic in the first half of the last century, but it could lead to blindness. Melarsoprol, developed in the 1950s, was the drug of first choice for the treatment of sleeping sickness for several decades and is still used today because there are no effective follow-up preparations available.
Also stimulated by the trypanosome-toxic effect of Atoxyl, Paul Ehrlich developed the arsenic-containing arsphenamine. The agent, introduced in 1910 for the treatment of syphilis, was the first antibiotic substance and was the model for the development of the sulfonamides that are still used today. It has also long been used in the treatment of dysentery.
In 2000, a preparation containing arsenic under the name Trisenox was approved in the USA for the treatment of promyelocytic leukemia (APL). Trisenox has been approved for the treatment of APL in Europe since 2002 (distribution in the EU and USA: Cephalon). Its effectiveness in cancer therapy is also attributed to its antiangioneogenic effect.
The various arsenic sulfides are components of medicinal products in Chinese medicine. Arsenicum album plays an important role in homeopathy, it is one of the so-called polychrests (often prescribed medicinal products).
Occurrence: Arsenic occurs practically everywhere in soil in low concentrations of up to 10 ppm. It is about as common in the earth's crust as beryllium and germanium. Of 1 million parts by mass, 1.5 can be assigned to arsenic; arsenic is thus in 53rd place in the table of the most common elements.
It is rarely found solid cobalt, as an elemental mineral it is found in massive form in Germany, the Harz Mountains (St. Andreasberg), the Ore Mountains (Freiberg), France, Italy, the USA and Russian Siberia. Intermetallic compounds with antimony (allemontite) and copper (whitneyite) are more common. Most of the time arsenic is found bound in the form of sulphides, mixed with other sulphide ores. The most common arsenic sulfides are realgar (As4S.4), Auripigment (As2S.3) and the main arsenic ore arsenic gravel (FeAsS), also known as arsenopyrite. Cobaltite ((Co, Fe) AsS), light red glow heart (Ag3AsS3), Gersdorffit, arsenic copper (Cu3As), lollingite, enargite (Cu3AsS4), Rammelsbergite as well as safflorite and sperrylite. Arsenates are often found in phosphate-containing rocks because they have a comparable solubility.
The main deposits of recoverable arsenic ores are today in Russia, Sweden, France, Mexico and Chile. Nevertheless, arsenic is mainly extracted in the context of the extraction of other metal ores such as copper, lead or cobalt, but also through phosphate mining. In 1986 there were about 48,000 tons of arsenic in the world in the form of As2O3 produced. According to the World Mineral Statistics of 1988, Sweden took the top position worldwide with a production capacity of 10,000 tons, followed by the then USSR (8100 tons), France (8000 tons), Mexico and Chile (6000 tons each). Other producers were Canada (5100 tons), Namibia (2200 tons) and Peru (1200 tons). Germany reached 360 tons in 1988. World reserves of arsenic are estimated at over 10 million tons.
Arsenic is only sparingly soluble in water and is therefore only found in small traces, around 1.6 ppb (billionths of a mass fraction) in seas and oceans.
Arsenic is found in the air in the form of particulate arsenic (III) oxide. Volcanic eruptions have been identified as the natural cause of this, releasing an estimated 3000 tons into the atmosphere. Bacteria release another 20,000 tons in the form of organic arsenic compounds such as trimethylarsine. A large part of the released arsenic also comes from the combustion of fossil fuels such as coal or crude oil. The estimated emissions caused by road traffic and stationary sources amounted to 120 tons in the Federal Republic of Germany in 1990 (20 tons in the old, 100 tons in the new federal states). The outdoor air concentration of arsenic is between 0.5 and 15 nanograms per cubic meter.
Frequency: 6,00 ⋅ 10-4 % (percentage by mass of the earth's shell, i.e. the earth's crust / oceans up to 16 km depth)
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