Sulfur

Sulfur is a chemical element with atomic number 16 and symbol S (from the Latin sulphur). It is an abundant nonmetal with a characteristic yellow color. This element is generated in massive stars in which temperatures prevail that cause the fusion between a silicon nucleus and a helium nucleus in a process called supernova nucleosynthesis.

Sulfur is found natively in volcanic regions and in its reduced forms forming sulfides and sulfosalts or in its oxidized forms as sulfates. It is an essential chemical constituent of the amino acids cysteine and methionine, and therefore necessary for the synthesis of proteins present in all living organisms. It is used mainly as a fertilizer, but also in the manufacture of gunpowder, laxatives, matches, and insecticides.

Main features

This nonmetal has a strong yellowish, brownish, or orange-green color and burns with a blue flame, giving off sulfur dioxide. It is insoluble in water, but it dissolves in carbon disulfide and benzene. It is multivalent, and oxidation states -2, +2, +4, +6 are common.

In all states (solid, liquid and gas): according to chemists it presents allotropic forms whose relationships are not completely known. The most common crystalline structures are the orthorhombic octahedron (α-sulfur) and the monoclinic prism (β-sulfur), with the transition temperature from one to the other being 96 °C; in both cases the sulfur is found forming ring-shaped S₈ molecules, and it is the different arrangement of these molecules that causes the different crystalline structures. At room temperature, the transformation of monoclinic to orthorhombic sulfur is more stable and very slow.

By melting sulfur, you get an easily flowing liquid made up of S₈ molecules. However, if heated, the color turns somewhat reddish brown, and the viscosity increases. This behavior is due to the breaking of the rings and the formation of long chains of sulfur atoms, which can reach several thousand atoms in length, which become entangled with each other, decreasing the fluidity of the liquid; the maximum of the viscosity is reached around 200 °C. Rapidly cooling this viscous liquid produces an elastic mass, with a consistency similar to that of rubber, called «plastic sulfur» (sulfur γ) made up of chains that have not had time to rearrange themselves to form S₈; after a certain time the mass loses its elasticity crystallizing in the rhombic system. Studies carried out with X-rays show that this deformed shape may be made up of S₈ molecules with a spiral helix structure.

In the vapor state it also forms S₈ molecules, but at 780 °C equilibrium with diatomic molecules is already reached and above approximately 1800 °C dissociation is complete and atoms of sulfur.

In addition to chunks, bars or coarse powder, there is a presentation on the market in the form of a very fine powder, called "Flower of sulfur", which can be obtained by precipitation in a liquid medium or by sublimation of its vapor on a cold metal plate.

Applications

Sulfur is used in many industrial processes, such as the production of sulfuric acid for batteries, the manufacture of gunpowder and the vulcanization of rubber.

Sulphites are used to bleach paper and in matches. Sodium or ammonium thiosulfate is used in the photographic industry as a 'fixer', since it dissolves silver bromide; and magnesium sulfate (Epsom salt) has various uses as a laxative, exfoliant, or nutritional supplement for plants.

Sulfur is also used in the oenological industry as an antiseptic. One of its main uses is as sulfur dioxide.

Sulfur has uses as a fungicide and in the manufacture of common phosphate fertilizers.

History

Sulfur (from the Latin sulphur, sulfŭris, linked to the Sanskrit śulbāri) has been known since Antiquity, and the Egyptians already used it. used to purify temples.

In Genesis (19,24), the Hebrews said that God (Yahweh) rained down brimstone and fire from heaven on Sodom and Gomorrah.

Homer recommended, in the 9th century B.C. C., avoid pestilence by burning sulfur (zeio in Greek, related to zeos-Zeus).

And Odysseus then spoke to the nodriza Euriclea, saying, Bring sulfur (zéeion), oh, old woman, remedy of the evil air, and bring fire, for I want to sulphur (zeeoso) the palace.

Homer, Odyssey (22, 480-483)

According to the Sanskrit-English Dictionary (1899) by Monier Monier-Williams, in Sanskrit sulfur was called śulbāri (pronounced /shulbári/), being śulba or śulva: 'copper', and a-rí or a-rís: 'enemy, envious' (lit. 'unliberal').

In Revelation 20:10 it says that the devil will be thrown into a lake of fire and brimstone.

Throughout the Middle Ages, Satan was linked to the odors of sulfurous gases released from volcanoes, which were supposed to be entrances to the subterranean hells).

Abundance and obtaining

Photograph of cast sulfur (top photo) and burning sulfur (bottom photo).

Sulfur is a very abundant element in the earth's crust, it is found in large quantities combined in the form of sulfides such as (pyrite and galena) and sulfates such as (gypsum). Natively it is found in the vicinity of hot springs, volcanic areas and in cinnabar, galena, sphalerite and stibnite mines, and in Louisiana (United States, the world's leading producer) it is extracted using the Frasch process consisting of injecting superheated steam to melt the sulfur that is later pumped abroad using compressed air. It is also obtained by separating it from natural gas, although it was previously obtained from deposits of pure sulfur impregnated with volcanic ash (Italy, and more recently Argentina).

It is also present, in small amounts, in fossil fuels (coal and oil) whose combustion produces sulfur dioxide that, combined with water, produces acid rain; To avoid this, the laws of industrialized countries require the reduction of the sulfur content of fuels, this sulfur, subsequently refined, constituting an important percentage of the total produced in the world. It is also extracted from natural gas that contains hydrogen sulfide that, once separated, is burned to obtain sulfur:

2 H₂S + O₂ → 2 S + 2 H₂O

The distinctive color of Io, Jupiter's volcanic moon, is due to the presence of different forms of sulfur in liquid, solid, and gaseous states. Sulfur is also found in several types of meteorites, and it is believed that the dark spot that can be seen near the lunar crater Aristarchus may be a deposit of sulfur.

World production in 2019, in millions of tons per year

1.	ChinaChina	17,5
2.	United States	8.7
3.	Russia Russia	7.5
4.	CanadaCanada	6.9
5.	Saudi ArabiaSaudi Arabia	6.5
6.	India	3.6
7.	Kazakhstan Kazakhstan	3.5
8.	JapanJapan	3.4
9.	United Arab Emirates United Arab Emirates	3.3
10.	South KoreaSouth Korea	3.0
11.	IranIran	2.2
12.	QatarQatar	1,8
13.	ChileChile	1.5
14.	PolandPoland	1.1.
15.	Australia	0.9
21.	BrazilBrazil	0.5

Source: USGS.

Oxidation states and compounds

The variety of sulfur compounds are the consequence of a great variety of possible oxidation states of the sulfur atom. The Table lists some examples of families of sulfur compounds, depending on the oxidation state of sulfur.

Human nose in general has a very high sensitivity to sulfur compounds, with odors that turn out to be unpleasant, so it detects these compounds even when they are in very small amounts. Thus, for example, the odors that the decomposition of organic matter gives rise to have their origin in the fact that their composition contains sulfur compounds, such as proteins that contain amino acids with sulfur (methionine, cysteine, cystine), which contain sulfur.

Sulfur dissolved in water is acidic (pK_a1 = 7.00, pK_a2 = 12.92) and reacts with metals. Metallic sulfides are found in nature, especially iron (pyrite) which can present negative resistance and galena, lead sulfide which is a natural semiconductor that was used as a rectifier.

Polymeric sulfur nitride (SN)_x, synthesized in 1975 by Alan G. MacDiarmid and Alan J. Heeger, has metallic properties, despite being made up of non-metals, and unusual properties electrical and optical. This work served as the basis for the subsequent development, with Hideki Shirakawa, of conductive plastics and semiconductors that led to the award of the Nobel Prize in Chemistry, in 2000, to the three researchers.

The most important oxides are sulfur dioxide, SO₂ (formed by the combustion of sulfur) which in water forms a solution of sulfurous acid, and sulfur trioxide, SO ₃, which in solution forms sulfuric acid; the sulfites and sulfates being the respective salts.

Isotopes

Dust sulfur Botámen of the first half of the 20th century. From the collection of the Museum of Object.

25 isotopes of sulfur are known, of which four are stable: S-32 (95.02%), S-33 (0.75%), S-34 (4.21%) and S-36 (0.025%). Apart from S-35, formed by the impact of cosmic radiation on atmospheric argon-40 and which has a half-life of 87 days, the other radioactive isotopes are short-lived.

Precautions

Carbon disulfide, hydrogen sulfide (commonly known as hydrogen sulfide), and sulfur dioxide should be handled with caution.

Hydrogen sulfide and some of its derivatives, mercaptans, are very toxic and can cause death in humans at very low concentrations in the environment (of the same order as hydrocyanic acid, used in executions with gas chamber in the United States, or much lower than carbon monoxide to cause death, and which is the source of numerous fatal poisonings with combustion heaters in poorly ventilated places). Although provided with "property notice" Because it is very malodorous even in concentrations well below that which causes death, it must be taken into account that when its concentration increases, the sense of smell quickly becomes saturated or narcotized, disappearing the smell, so potential victims of exposure may not be aware of its airborne presence until its potentially fatal effects are manifested.

As with hydrocyanic acid salts, cyanides, hydrogen sulfide salts, and sulfides must be handled with great care, preventing them from coming into contact with acids or acid solutions (even slightly acid), which would give rise to the release of toxic hydrogen sulfide.

Sulfur dioxide reacts with atmospheric water to produce acid rain. Irritates mucus and eyes and causes coughing when inhaled.

Sulfuric acid vapors can cause hemorrhaging in the lungs, filling them with blood and suffocating.

Sulfur in the plastic arts

Sulphur-based soap.

In goldsmithing, the use of sulfur is widespread, in particular for the oxidation of silver, that is, for the creation of the patina (black colour).

There are several techniques for this purpose; One of these is to mix powdered sulfur with a fatty material —Vaseline, oil—, apply the ointment to the piece of silver and, using a blowtorch, heat the metal and the mixture until it turns black. Subsequently, wash with water and neutral soap. The patination is durable.

Silver can be patinated in the same way with potassium sulfate and water.