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Hydrogen sulfide
Identifiers
CAS number 7783-06-4 Yes check.svgY
PubChem 402
ChemSpider 391
EC number 231-977-3
UN number 1053
RTECS number MX1225000
Properties
Molecular formula H2S
Molar mass 34.082 g/mol
Appearance Colorless gas.
Density 1.363 g/L, gas.
Melting point

-82.30 °C (190.85 K)

Boiling point

-60.28 °C (212.87 K)

Solubility in water 0.4 g/100 mL (20 °C)
0.25 g/100 mL (40 °C)
Solubility soluble in CS2, methanol, acetone;
very soluble in alkanolamine
Acidity (pKa) 6.89
19±2 (see text)
Refractive index (nD) 1.000644 (0 °C) [1]
Structure
Molecular shape Bent
Dipole moment 0.97 D
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-20.599 kJ/mole
Specific heat capacity, C 1.003 J/g K
Hazards
EU Index 016-001-00-4
EU classification Highly Flammable (F+)
Very Toxic (T+)
Dangerous for the environment (N)
R-phrases R12, R26, R50
S-phrases (S1/2), S9, S16, S36, S38, S45, S61
NFPA 704
NFPA 704.svg
4
4
0
Flash point flammable gas
Autoignition
temperature
260 °C
Explosive limits 4.3–46%
Related compounds
Related hydrogen chalcogenides Water
Hydrogen selenide
Hydrogen telluride
Hydrogen disulfide
Related compounds Phosphine
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hydrogen sulfide (or hydrogen sulphide) is the chemical compound with the formula H2S. It is a colorless, very poisonous, flammable gas with the characteristic foul odor of rotten eggs. It often results from the bacterial break down of organic matter in the absence of oxygen, such as in swamps and sewers (anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters. The body produces small amounts of H2S and uses it as a signaling molecule.

Hydrogen sulfide has numerous names, some of which are archaic (see table).

Contents

Properties

Hydrogen sulfide is slightly heavier than air; a mixture of H2S and air is explosive. Hydrogen sulfide and oxygen burn with blue flame to form sulfur dioxide (SO2) and water. In general it acts as a reducing agent.

At high heat or in the presence of catalysts, sulfur dioxide can be made to react with hydrogen sulfide to form elemental sulfur and water. This is exploited in the Claus process, the main way to convert hydrogen sulfide into elemental sulfur.

Hydrogen sulfide is somewhat soluble in water and acts as a weak acid, giving the hydrosulfide ion HS (pKa=6.9 in 0.01-0.1 mol/litre solutions at 18°C) and the sulfide ion S2− (pKa=11.96). A solution of hydrogen sulfide in water is initially clear but over time turns cloudy. This is due to the slow reaction of hydrogen sulfide with the oxygen dissolved in water, yielding elemental sulfur which precipitates out.

Hydrogen sulfide reacts with metal ions to form metal sulfides, which may be considered the salts of hydrogen sulfide. Some ores are sulfides. Metal sulfides often have a dark color. Lead(II) acetate paper is used to detect hydrogen sulfide because it turns grey in the presence of the gas as lead(II) sulfide is produced. Reacting metal sulfides with strong acid liberates hydrogen sulfide.

Production

Hydrogen sulfide is most commonly obtained by its separation from sour gas, which is natural gas with high content of H2S. It can also be produced by reacting hydrogen gas with molten elemental sulfur at about 450 °C. Hydrocarbons can replace hydrogen in this process.[2]

Sulfate-reducing bacteria (resp. sulfur-reducing bacteria) generate usable energy under low-oxygen conditions by using sulfates (resp. elemental sulfur) to oxidize organic compounds or hydrogen; this produces hydrogen sulfide as a waste product.

The standard lab preparation is to gently heat ferrous sulfide (FeS) with a strong acid in a Kipp generator. A less well known and more convenient alternative is to react aluminium sulfide with water:

3 H2O + Al2S3 → 3 H2S + Al2O3.

Hydrogen sulfide is also a byproduct of some reactions and caution should be used when production is likely as exposure can be fatal.

Occurrence

Deposit of sulfur on a rock, caused by volcanic gases

Small amounts of hydrogen sulfide occur in crude petroleum, but natural gas can contain up to 90%.[3] Volcanoes and some hot springs (as well as cold springs) emit some H2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H2O → MO + H2S.

About 10% of total global emissions of H2S is due to human activity. By far the largest industrial route to H2S occurs in petroleum refineries: the hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H2S is converted to elemental sulfur by partial combustion via the Claus process, which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the sulfate method), and tanneries. H2S arises from virtually anywhere where elemental sulfur comes into contact with organic material, especially at high temperatures.

Hydrogen sulfide can be present naturally in well water. In such cases, ozone is often used for its removal. An alternative method uses a filter with manganese dioxide. Both methods oxidize sulfides to less toxic sulfates.

Uses

Production of thioorganic compounds

Several organosulfur compounds are produced using hydrogen sulfide. These include methanethiol, ethanethiol, and thioglycolic acid.

Alkali metal sulfides

Upon combining with alkali metal bases, hydrogen sulfide converts to alkali hydrosulfides such as sodium hydrosulfide and sodium sulfide, which are used in the degradation of biopolymers. The depilation of hides and the delignification of pulp by the Kraft process both are effected by alkali sulfides.

In analytical chemistry

Hydrogen sulfide used to have importance in analytical chemistry for well over a century, in the qualitative inorganic analysis of metal ions. In these analyses, heavy metal (and nonmetal) ions (e.g. Pb(II), Cu(II), Hg(II), As(III)) are precipitated from solution upon exposure to H2S. The components of the resulting precipitate redissolve with some selectivity.

For small-scale laboratory use in analytic chemistry, the use of thioacetamide has superseded H2S as a source of sulfide ions.

A precursor to metal sulfides

As indicated above, many metal ions react with hydrogen sulfide to give the corresponding metal sulfides. This conversion is widely exploited. For example gases or waters contaminated by hydrogen sulfide can be cleaned with metal sulfides. In the purification of metal ores by flotation, mineral powders are often treated with hydrogen sulfide to enhance the separation. Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide, and the behavior of metallic catalysts used in other parts of a refinery is also modified using hydrogen sulfide.

Miscellaneous applications

Hydrogen sulfide is also used in the separation of deuterium oxide, i.e. heavy water, from normal water via the Girdler Sulfide process.

Removal from fuel gases

Hydrogen sulfide is commonly found in natural gas, biogas, and LPG. It can be removed in a number of ways.

Reaction with iron oxide

Gas is pumped through a container of hydrated iron(III) oxide which combines with hydrogen sulfide.

Fe2O3(s) + H2O(l) + 3 H2S(g) → Fe2S3(s) + 4 H2O(l)

In order to regenerate iron(III) oxide, the container must be taken out of service, flooded with water and aerated.

2 Fe2S3(s) + 3 O2(g) + 2 H2O(l) → 2 Fe2O3(s) + H2O(l) + 6 S(s)

On completion of the regeneration reaction the container is drained of water and can be returned to service.

The advantage of this system is that it is completely passive during the extraction phase.[4]

Hydrodesulfurization

Hydrodesulfurization is a more complex method of removing sulfur from fuels.

Safety

Hydrogen sulfide is a highly toxic and flammable gas. Being heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so potential victims may be unaware of its presence until it is too late. For safe handling procedures, a hydrogen sulfide material safety data sheet (MSDS) should be consulted.[5]

Toxicity

Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thereby blocking oxygen from binding and stopping cellular respiration. Since hydrogen sulfide occurs naturally in the environment and the gut, enzymes exist in the body capable of detoxifying it by oxidation to (harmless) sulfate.[6] Hence, low levels of sulfide may be tolerated indefinitely.

At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm.

An interesting diagnostic clue of extreme poisoning by H2S is the discoloration of copper coins in the pockets of the victim. Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some cases hyperbaric oxygen therapy (HBO). HBO therapy has anecdotal support and remains controversial.[7][8][9]

Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs. These symptoms usually go away in a few weeks. Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Chronic exposure to low level H2S (around 2 ppm) has been implicated in increased miscarriage and reproductive health issues among Russian and Finnish wood pulp workers, but the reports have not (as of circa 1995) been replicated.

  • 0.0047 ppm is the recognition threshold, the concentration at which 50% of humans can detect the characteristic odor of hydrogen sulfide [1], normally described as resembling "a rotten egg".
  • Less than 10 ppm has an exposure limit of 8 hours per day.
  • 10–20 ppm is the borderline concentration for eye irritation.
  • 50–100 ppm leads to eye damage.
  • At 150–250 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger.
  • 320–530 ppm leads to pulmonary edema with the possibility of death.
  • 530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing.
  • 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure (LC50).
  • Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.

Hydrogen sulfide was used by the British as a chemical agent during World War One. It was not considered to be an ideal war gas, but while other gases were in short supply it was used on two occasions in 1916.[10] The gas, produced by mixing certain household ingredients, was used in a suicide wave in 2008, primarily in Japan.[11]

Function in the body

Hydrogen sulfide is produced in small amounts by some cells of the mammalian body and has a number of biological signaling functions. (Only two other such gases are currently known: nitric oxide (NO) and carbon monoxide (CO).)

The gas is produced from cysteine by the enzymes cystathionine beta-synthase and cystathionine gamma-lyase. It acts as a relaxant of smooth muscle and as a vasodilator[12] and is also active in the brain, where it increases the response of the NMDA receptor and facilitates long term potentiation[13], which is involved in the formation of memory.

Eventually the gas is converted to sulfite in the mitochondria by thiosulfate reductase, and the sulfite is further oxidized to thiosulfate and sulfate by sulfite oxidase. The sulfates are excreted in the urine.[14]

Due to its effects similar to nitric oxide (without its potential to form peroxides by interacting with superoxide), hydrogen sulfide is now recognized as potentially protecting against cardiovascular disease.[12] The cardioprotective role effect of garlic is caused by catabolism of the polysulfide group in allicin to H2S, a reaction which could depend on reduction mediated by glutathione.[15]

Like nitric oxide, hydrogen sulfide is involved in the relaxation of smooth muscle that causes erection of the penis, presenting possible new therapy opportunities for erectile dysfunction.[16][17]

In Alzheimer's disease the brain's hydrogen sulfide concentration is severely decreased.[18] In trisomy 21 (the most common form of Down syndrome) the body produces an excess of hydrogen sulfide.[14]

Induced hypothermia

In 2005 it was shown that mice can be put into a state of suspended animation-like hypothermia by applying a low dosage of hydrogen sulfide (81 ppm H2S) in the air. The breathing rate of the animals sank from 120 to 10 breaths per minute and their temperature fell from 37 °C to just 2 °C above ambient temperature (in effect, they had become cold-blooded). The mice survived this procedure for 6 hours and afterwards showed no negative health consequences.[19] In 2006 it was shown that the blood pressure of mice treated in this fashion with hydrogen sulfide did not significantly decrease.[20]

A similar process known as hibernation occurs naturally in many mammals and also in toads, but not in mice. (Mice can fall into a state called clinical torpor when food shortage occurs). If the H2S-induced hibernation can be made to work in humans, it could be useful in the emergency management of severely injured patients, and in the conservation of donated organs. In 2008, hypothermia induced by hydrogen sulfide for 48 hours was shown to reduce the extent of brain damage caused by experimental stroke in rats.[21]

As mentioned above, hydrogen sulfide binds to cytochrome oxidase and thereby prevents oxygen from binding, which leads to the dramatic slowdown of metabolism. Animals and humans naturally produce some hydrogen sulfide in their body; researchers have proposed that the gas is used to regulate metabolic activity and body temperature, which would explain the above findings.[22]

Two recent studies cast doubt that the effect can be achieved in larger mammals. A 2008 study failed to reproduce the effect in pigs, concluding that the effects seen in mice were not present in larger mammals.[23] Likewise a paper by Haouzi et al noted that there is no induction of hypometabolism in sheep, either.[24]

Participant in the sulfur cycle

Hydrogen sulfide is a central participant in the sulfur cycle, the biogeochemical cycle of sulfur on Earth.

In the absence of oxygen, sulfur-reducing and sulfate-reducing bacteria derive energy from oxidizing hydrogen or organic molecules by reducing sulfur or sulfate to hydrogen sulfide. Other bacteria liberate hydrogen sulfide from sulfur-containing amino acids; this gives rise to the odor of rotten eggs and contributes to the odor of flatulence.

Sludge from a pond; the black color is due to metal sulfides

As organic matter decays under low-oxygen (or hypoxic) conditions (such as in swamps, eutrophic lakes or dead zones of oceans), sulfate-reducing bacteria will use the sulfates present in the water to oxidize the organic matter, producing hydrogen sulfide as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water soluble. These metal sulfides, such as ferrous sulfide FeS, are often black or brown, leading to the dark color of sludge.

Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using dissolved oxygen, metal oxides (e.g. Fe oxyhydroxides and Mn oxides) or nitrate as oxidant.[25]

The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as electron donor in photosynthesis, thereby producing elemental sulfur. (In fact, this mode of photosynthesis is older than the mode of cyanobacteria, algae and plants which uses water as electron donor and liberates oxygen.)

H2S implicated in mass extinctions

Hydrogen sulfide has been implicated in some of the several mass extinctions that have occurred in the Earth's past. In particular, a buildup of hydrogen sulfide in the atmosphere may have caused the Permian-Triassic extinction event 252 million years ago.[26]

Organic residues from these extinction boundaries indicate that the oceans were anoxic (oxygen depleted) and had species of shallow plankton that metabolized H2S. The formation of H2S may have been initiated by massive volcanic eruptions, which emitted CO2 and methane into the atmosphere which warmed the oceans, lowering their capacity to absorb oxygen which would otherwise oxidize H2S. The increased levels of hydrogen sulfide could have killed oxygen-generating plants as well as depleted the ozone layer causing further stress. Small H2S blooms have been detected in modern times in the Dead Sea and in the Atlantic ocean off the coast of Namibia.[26]

See also

References

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
  2. ^ Jacques Tournier-Lasserve "Hydrogen Sulfide" in Ullmann's Encyclopedia of Chemical Industry
  3. ^ "Burden of the Beasts: Ranchers wonder why Their Livestock Suffer and Die," Houston Chronicle, http://www.chron.com/content/chronicle/nation/h2s/alberta.html
  4. ^ http://www.marcabcoinc.com/page2.html
  5. ^ Iowa State University, Department of Chemistry MSDS, Hydrogen Sulfide Material Safety Data Sheet, http://avogadro.chem.iastate.edu/MSDS/hydrogen_sulfide.pdf, retrieved 2009-03-14 
  6. ^ S. Ramasamy, S. Singh, P. Taniere, M. J. S. Langman, M. C. Eggo (2006). "Sulfide-detoxifying enzymes in the human colon are decreased in cancer and upregulated in differentiation". Am J Physiol Gastrointest Liver Physiol 291: G288–G296. doi:10.1152/ajpgi.00324.2005. PMID 16500920. http://ajpgi.physiology.org/cgi/content/full/291/2/G288. Retrieved 2007-10-20. 
  7. ^ Gerasimon G, Bennett S, Musser J, Rinard J (May 2007). "Acute hydrogen sulfide poisoning in a dairy farmer". Clin Toxicol (Phila) 45 (4): 420–3. doi:10.1080/15563650601118010. PMID 17486486. http://www.informaworld.com/openurl?genre=article&doi=10.1080/15563650601118010&magic=pubmed. Retrieved 2008-07-22. 
  8. ^ Belley R, Bernard N, Côté M, Paquet F, Poitras J (July 2005). "Hyperbaric oxygen therapy in the management of two cases of hydrogen sulfide toxicity from liquid manure". CJEM 7 (4): 257–61. PMID 17355683. http://caep.ca/template.asp?id=BD7EF8164B8A4759A57CF8EA67E404B0. Retrieved 2008-07-22. 
  9. ^ Hsu P, Li H-W, Lin Y-T (1987). "Acute hydrogen sulfide poisoning treated with hyperbaric oxygen.". J. Hyperbaric Med 2 (4): 215–221. ISSN 0884-1225. http://archive.rubicon-foundation.org/4354. Retrieved 2008-07-22. 
  10. ^ Foulkes, Charles Howard (2001) [First published Blackwood & Sons, 1934]. "Gas!" The Story of the Special Brigade. Published by Naval & Military P.. p. 105. ISBN 1-84342-088-0. 
  11. ^ Dangerous Japanese ‘Detergent Suicide’ Technique Creeps Into U.S., March 13, 2009, http://www.wired.com/threatlevel/2009/03/japanese-deterg/ 
  12. ^ a b Lefer, David J. (November 2007). "A new gaseous signaling molecule emerges: Cardioprotective role of hydrogen sulfide.". PNAS 104: 17907–17908. doi:10.1073/pnas.0709010104. http://www.pnas.org/content/104/46/17907.full. Retrieved 2008-09-26. 
  13. ^ Kimura, Hideo (2002). "Hydrogen sulfide as a neuromodulator". Molecular Neurobiology 26 (1): 13-19. doi:10.1385/MN:26:1:013. 
  14. ^ a b Kamoun, Pierre (2004-07). "[H2S, a new neuromodulator]". Médecine Sciences: M/S 20 (6-7): 697-700. PMID 15329822. 
  15. ^ Benavides, Gloria A; Giuseppe L Squadrito, Robert W Mills, Hetal D Patel, T Scott Isbell, Rakesh P Patel, Victor M Darley-Usmar, Jeannette E Doeller, David W Kraus (2007-11-13). "Hydrogen sulfide mediates the vasoactivity of garlic". Proceedings of the National Academy of Sciences of the United States of America 104 (46): 17977-17982. doi:10.1073/pnas.0705710104. PMID 17951430. 
  16. ^ Roberta d'Emmanuele di Villa Biancaa, Raffaella Sorrentinoa, Pasquale Maffiaa, Vincenzo Mironeb, Ciro Imbimbob, Ferdinando Fuscob, Raffaele De Palmad, Louis J. Ignarroe und Giuseppe Cirino (2009), "Hydrogen sulfide as a mediator of human corpus cavernosum smooth-muscle relaxation", PNAS, doi:10.1073/pnas.0807974105, PMID 19255435 
  17. ^ "Hydrogen Sulfide: Potential Help for ED", WebMD, March 2, 2009, http://www.webmd.com/erectile-dysfunction/news/20090302/hydrogen-sulfide-potential-help-for-ed 
  18. ^ Eto, Ko; Takashi Asada, Kunimasa Arima, Takao Makifuchi, Hideo Kimura (2002-05-24). "Brain hydrogen sulfide is severely decreased in Alzheimer's disease". Biochemical and Biophysical Research Communications 293 (5): 1485-1488. doi:10.1016/S0006-291X(02)00422-9. http://www.ncbi.nlm.nih.gov/pubmed/12054683. 
  19. ^ Mice put in 'suspended animation', BBC News, 21 April 2005
  20. ^ Gas induces 'suspended animation', BBC News, 9 October 2006
  21. ^ Florian B, Vintilescu R, Balseanu AT, Buga A-M, Grisk O, Walker LC, Kessler C, Popa-Wagner A (2008). "Long-term hypothermia reduces infarct volume in aged rats after focal ischemia". Neuroscience Letters 438: 180–185. doi:10.1016/j.neulet.2008.04.020. PMID 18456407. 
  22. ^ Mark B. Roth and Todd Nystul. Buying Time in Suspended Animation. Scientific American, 1 June 2005
  23. ^ Li, Jia; Zhang, Gencheng; Cai, Sally; Redington, Andrew N (January 2008). "Effect of inhaled hydrogen sulfide on metabolic responses in anesthetized, paralyzed, and mechanically ventilated piglets.". Pediatric Critical Care Medicine 9 (1): 110–112. doi:10.1097/01.PCC.0000298639.08519.0C. http://www.pccmjournal.com/pt/re/pccm/abstract.00130478-200801000-00021.htm. Retrieved 2008-02-07. "H2S does not appear to have hypometabolic effects in ambiently cooled large mammals and conversely appears to act as a hemodynamic and metabolic stimulant.". 
  24. ^ Haouzi P, Notet V, Chenuel B, Chalon B, Sponne I, Ogier V et al. (2008). "H2S induced hypometabolism in mice is missing in sedated sheep.". Respir Physiol Neurobiol 160 (1): 109-15. doi:10.1016/j.resp.2007.09.001. PMID 17980679. http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&retmode=ref&cmd=prlinks&id=17980679. 
  25. ^ Jørgensen, B. B. & D. C. Nelson (2004) Sulfide oxidation in marine sediments: Geochemistry meets microbiology, pp. 36–81. In J. P. Amend, K. J. Edwards, and T. W. Lyons (eds.) Sulfur Biogeochemistry - Past and Present. Geological Society of America.
  26. ^ a b "Impact From the Deep" in the October 2006 issue of Scientific American.

Additional resources

  • "Hydrogen Sulfide", Committee on Medical and Biological Effects of Environmental Pollutants, University Park Press, 1979, Baltimore. ISBN 0-8391-0127-9

External links


Simple English

Hydrogen sulfide
[[File:|150px|Hydrogen sulfide's geometry]] [[File:|100px|Hydrogen sulfide]]
General
Systematic name Hydrogen sulfide, sulfane
Other names Sulfuretted hydrogen
Molecular formula H2S
Molar mass 34.082 g/mol
Appearance Colorless gas.
CAS number
Properties
Density and phase 1.363 g/L, gas.
Solubility in water 0.25 g/100 ml (40 °C)
Melting point −82.30 °C (190.85 K)
Boiling point −60.28 °C (212.87 K)
Acidity (pKa) 6.89
19±2 (See Text)
Structure
Molecular shape Bent.
Dipole moment 0.97 D
Hazards
MSDS External MSDS
Main hazards Highly toxic, highly flammable.
NFPA 704

4
4
0
 
Flash point −82.4 °C
R/S statement R:
RTECS number MX1225000
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Inorganic derivatives sodium sulfide
sodium hydrosulfide
Organic derivatives dimethyl sulfide
Related hydrogen compounds water
hydrogen selenide
hydrogen telluride
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul smell of rotten eggs and flatulence. It often results when bacteria break down organic matter in the absence of oxygen. This happens in swamps, and sewers (alongside the process of anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters. This is the smell that people often think to be that of sulfur. But sulfur itself does not smell.

Hydrogen sulfide is also known as sulfane, sulfur hydride, sour gas, sulfurated hydrogen, hydrosulfuric acid, sewer gas and stink damp. IUPAC accepts the names "hydrogen sulfide" and "sulfane". When people speak of more complicated compounds they always use the term "sulfane".

Contents

Occurrence

File:Deposit from hydrogen
Deposit of sulfur on a rock, caused by volcanic gases containing hydrogen sulfide

Small amounts of hydrogen sulfide can be found in crude petroleum but natural gas can contain up to 28%. Volcanoes and hot springs emit some H2S, where it probably arises via the hydrolysis of sulfide minerals, i.e. MS + H2O to give MO + H2S.

Normal average concentration in clean air is about 0.0001-0.0002 ppm.

Safety

Hydrogen sulfide is a highly toxic and flammable gas. Because it is heavier than air it tends to accumulate at the bottom of poorly ventilated spaces.

Toxicity

Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide.

Reference

  • "Hydrogen Sulfide", Committee on Medical and Biological Effects of Environmental Pollutants, University Park Press, 1979, Baltimore. ISBN 0-8391-0127-9

Other websites








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