- Structure
- Nomenclature
- Physical properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Density
- Solubility
- Chemical properties
- In aqueous solution
- Reaction with oxygen
- Reaction with metals
- Reaction with sulfur dioxide
- Decomposition with temperature
- Location in nature
- Synthesis in the mammalian organism
- Obtaining in the laboratory or industrially
- Industrial use of H
- Usefulness or importance of H
- Cardiovascular system
- Gastrointestinal system
- Central Nervous System
- Organ of vision
- Against aging
- Healing potential of H
- Risks
- References
The hydrogen sulfide or hydrogen sulfide gas is formed by the union of a sulfur atom (S) and two hydrogen atoms (H). Its chemical formula is H 2 S. It is also known as hydrogen sulfide gas. It is a colorless gas whose odor is evident in rotten eggs.
It is present in volcanoes and sulphurous hot springs, in natural gas and in crude oil. It is also formed during the anaerobic decomposition (without oxygen) of plant and animal organic matter. It occurs naturally in the mammalian body, through the action of certain enzymes on cysteine, a non-essential amino acid.
Chemical formula of hydrogen sulfide or hydrogen sulfide. SARANPHONG YIMKLAN. Source: Wikimedia Commons.
Aqueous H 2 S solutions are corrosive to metals such as steel. H 2 S is a reducing compound that, when reacting with SO 2, oxidizes to elemental sulfur while reducing SO 2 to sulfur as well.
Despite being a highly toxic and fatal compound for humans and animals, its importance in a series of important processes in the body has been studied for some years.
It regulates a series of mechanisms related to the generation of new blood vessels and the functioning of the heart.
It protects neurons and has been thought to act against diseases such as Parkinson's and Alzheimer's.
Due to its chemical reducing capacity, it can combat oxidant species, thus acting against cellular aging. Due to these reasons, the possibility of producing drugs that when administered to patients can be released slowly into the body is being studied.
This would serve to treat pathologies such as ischemia, diabetes and neurodegenerative diseases. However, its mechanism of action and its safety have yet to be thoroughly investigated.
Structure
The H 2 S molecule is analogous to that of water, that is, they are similar in shape since the hydrogens are located at an angle with the sulfur.
Angular structure of the hydrogen sulfide molecule, H 2 S. Bangin. Source: Wikimedia Commons.
Sulfur in H 2 S has the following electronic configuration:
1s 2, 2s 2 2p 6, 3s 2 3p 6, Well, it borrows one electron from each hydrogen to complete its valence shell.
3D structure of hydrogen sulfide. Yellow: sulfur. White: hydrogen. Benjah-bmm27. Source: Wikimedia Commons.
Nomenclature
- Hydrogen sulfide
- Hydrogen sulfide
- Sulfur hydride.
Physical properties
Physical state
Colorless gas with a very unpleasant odor.
Molecular weight
34.08 g / mol.
Melting point
-85.60 ° C.
Boiling point
-60.75 ° C.
Density
1.1906 g / L.
Solubility
Moderately soluble in water: 2.77 volumes in 1 of water at 20ºC. It can be dislodged from the aqueous solution completely by boiling it.
Chemical properties
In aqueous solution
When hydrogen sulfide is in aqueous solution, it is called hydrogen sulfide. It is a weak acid. It has two ionizable protons:
H 2 S + H 2 O ⇔ H 3 O + + HS -, K a1 = 8.9 x 10 -8
HS - + H 2 O ⇔ H 3 O + + S 2 -, K a2 ∼ 10 -14
The first proton ionizes slightly, as can be deduced from its first ionization constant. The second proton ionizes very little, but solutions of H 2 S contain some of the sulfide anion S 2 -.
If the H 2 S solution is exposed to air, the O 2 oxidizes the sulfide anion and sulfur precipitates:
2 S 2 - + 4 H + + O 2 → 2 H 2 O + 2 S 0 ↓ (1)
In the presence of chlorine Cl 2, bromine Br 2 and iodine I 2, the corresponding hydrogen halide and sulfur are formed:
H 2 S + Br 2 → 2 HBr + S 0 ↓ (2)
Aqueous H 2 S solutions are corrosive, causing sulfide stress cracking in high hardness steels. The corrosion products are iron sulfide and hydrogen.
Reaction with oxygen
H 2 S reacts with oxygen in the air and the following reactions can occur:
2 H 2 S + 3 O 2 → 2 H 2 O + 2 SO 2 (3)
2 H 2 S + O 2 → 2 H 2 O + 2 S 0 ↓ (4)
Reaction with metals
It reacts with various metals that displace hydrogen and forms the metal sulfide:
H 2 S + Pb → PbS + H 2 ↑ (5)
Reaction with sulfur dioxide
In volcanic gases, H 2 S and SO 2 are present, which react with each other and solid sulfur is formed:
H 2 S + SO 2 → 2 H 2 O + 3 S 0 ↓ (6)
Decomposition with temperature
Hydrogen sulfide is not very stable, it decomposes easily when heated:
H 2 S → H 2 ↑ + S 0 ↓ (7)
Location in nature
This gas is found naturally in sulphurous or sulphurous hot springs, in volcanic gases, in crude oil and in natural gas.
Sulphurous water spring. Николай Максимович. Source: Wikimedia Commons.
When oil (or gas) contains significant traces of H 2 S it is said to be "sour", in contrast to "sweet", which is when it does not contain it.
Small amounts of H 2 S in oil or gas are economically detrimental because a scrubbing plant must be installed to remove it, both to prevent corrosion and to make the waste gas safe for domestic use as a fuel.
It is produced whenever organic matter containing sulfur decomposes under anaerobic conditions (absence of air), such as human, animal and plant waste.
H 2 S emissions (teal color) off the coast of Namibia, photographed by NASA. These emissions come from organic waste. NASA's Earth Observatory. Source: Wikimedia Commons.
The bacteria present in the mouth and in the gastrointestinal tract produce it from the degradable materials that plant or animal proteins contain.
Its characteristic smell makes its presence visible in rotten eggs.
H 2 S is also produced in certain industrial activities, such as oil refineries, coke ovens, paper mills, tanneries, and in food processing.
Synthesis in the mammalian organism
Endogenous H 2 S can be produced in mammalian tissues, including humans, in two ways, one enzymatic and one non-enzymatic.
The non-enzymatic pathway consists of the reduction of elemental sulfur S 0 to H 2 S through the oxidation of glucose:
2 C 6 H 12 O 6 (glucose) + 6 S 0 (sulfur) + 3 H 2 O → 3 C 3 H 6 O 3 + 6 H 2 S + 3 CO 2 (8)
The enzymatic pathway consists of the production of H 2 S from L-cysteine, which is an amino acid synthesized by the body. The process is ensured by various enzymes, such as cystathionine-β-synthase and cystathionine-γ-lyase, among others.
Hydrogen sulfide has been found in the brains of cows. Author: ArtTower. Source: Pixabay.
Obtaining in the laboratory or industrially
Hydrogen gas (H 2) and the element sulfur (S) do not react at normal ambient temperatures, but above these they begin to combine, with 310 ºC being the optimum temperature.
The process is, however, too slow, so other methods are used to obtain it, including the following.
Metal sulfides (such as ferrous sulfide) are reacted with acids (such as hydrochloric) in dilute solution.
FeS + 2 HCl → FeCl 2 + H 2 S ↑ (9)
In this way, the H 2 S gas is obtained, which, given its toxicity, must be collected safely.
Industrial use of H
The storage and transportation in large quantities of the H 2 S that is separated from natural gas by washing with amines is difficult, therefore the Claus process is used to convert it into sulfur.
In oil refineries, H 2 S is separated from natural gas by washing with amines and then converted to sulfur. Author: SatyaPrem. Source: Pixabay.
In this process two reactions occur. In the first, H 2 S reacts with oxygen to give SO 2, as mentioned above (see reaction 3).
The second is an iron oxide catalyzed reaction where SO 2 is reduced and H 2 S is oxidized, both of which produce sulfur S (see reaction 6).
In this way sulfur is obtained which can be easily stored and transported, as well as destined for multiple uses.
Usefulness or importance of H
Endogenous H 2 S is that which occurs naturally in the body as part of normal metabolism in humans, mammals and other living beings.
Despite its long-standing reputation as a toxic and poisonous gas associated with the decomposition of organic matter, several recent studies from the 2000s to the present have determined that endogenous H 2 S is an important regulator of certain mechanisms. and processes in the living being.
H 2 S has a high lipophilicity or affinity towards fats, which is why it crosses cell membranes easily, penetrating all types of cells.
Cardiovascular system
In mammals, hydrogen sulfide promotes or regulates a series of signals that regulate metabolism, cardiac function, and cell survival.
It has a powerful effect on the heart, blood vessels and circulating elements of the blood. Modulates cellular metabolism and mitochondrial function.
It defends the kidneys from damage caused by ischemia.
Gastrointestinal system
It plays an important role as a protective factor against damage to the gastric mucosa. It is believed that it may be an important mediator of gastrointestinal motility.
It is likely involved in the control of insulin secretion.
Central Nervous System
It also acts in important functions of the central nervous system and protects neurons from oxidative stress.
Neurons are protected by endogenous H 2 S. Author: Gerd Altmann. Source: Pixabay.
It is estimated that it can protect against neurodegenerative diseases such as Parkinson's, Alzheimer's and Hungtinton's disease.
Organ of vision
It protects the photoreceptor cells of the retina from light-induced degeneration.
Against aging
H 2 S, being a reducing species, can be consumed by a variety of oxidizing agents that circulate in the body. It fights oxidizing species such as reactive oxygen species and reactive nitrogen species in the body.
It limits the reactions of free radicals through the activation of antioxidant enzymes that protect against the effects of aging.
Healing potential of H
The bioavailability of endogenous H 2 S depends on certain enzymes involved in the biosynthesis of cysteine in mammals.
Some studies suggest that therapy drugs donors H 2 S may be beneficial in certain diseases.
For example, it could be useful in diabetic patients, since it has been observed that the blood vessels of diabetic animals improve with drugs that supply exogenous H 2 S.
H 2 S supplied exogenously increases angiogenesis or blood vessel formation, so it could be used for the treatment of chronic ischemic diseases.
Drugs are being devised that can release H 2 S slowly in order to act beneficially on various diseases. However, the efficacy, safety and mechanisms of its action have yet to be investigated.
Risks
H 2 S is a fatal poison if inhaled neat or even diluted 1 part of gas in 200 parts of air. Birds are very sensitive to H 2 S and die even at dilution of 1 in 1500 parts of air.
Hydrogen sulfide or hydrogen sulfide H 2 S is a powerful poison. Author: OpenIcons. Source: Pixabay.
H 2 S is a potent inhibitor of certain enzymes and oxidative phosphorylation processes, leading to cell suffocation. Most people smell it at concentrations greater than 5 ppb (parts per billion). Concentrations of 20-50 ppm (parts per million) are irritating to the eyes and respiratory tract.
An inhalation of 100-250 ppm for a few minutes can cause incoordination, memory disorders and motor disorders. When the concentration is around 150-200 ppm, olfactory fatigue or anosmia occurs, which means that afterwards the characteristic smell of H 2 S cannot be detected. If a concentration of 500 ppm is inhaled for 30 minutes, pulmonary edema can occur. and pneumonia.
Concentrations of more than 600 ppm can be fatal within the first 30 minutes, as the respiratory system is paralyzed. And 800 ppm is the concentration that is immediately lethal to humans.
H 2 S must therefore be prevented from escaping in laboratories, premises or in any place or situation.
It is important to note that many deaths occur because people enter confined spaces to rescue co-workers or family members who have collapsed due to H 2 S poisoning, and they also die.
It is a flammable gas.
References
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