Carbonyl Sulfide
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Carbonyl sulfide is the
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the linear formula . It is a colorless flammable gas with an unpleasant
odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...
. It is a linear molecule consisting of a carbonyl double bonded to a sulfur atom. Carbonyl sulfide can be considered to be intermediate between
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
and carbon disulfide, both of which are valence isoelectronic with it.


Occurrence

Carbonyl sulfide is the most abundant sulfur compound naturally present in the atmosphere, at , because it is emitted from oceans,
volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...
es and deep sea vents. As such, it is a significant compound in the global sulfur cycle. Measurements on the
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
ice cores and from air trapped in snow above glaciers ( firn air) have provided a detailed picture of OCS concentrations from 1640 to the present day and allow an understanding of the relative importance of
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Anthropogenic may also refer to things that have been generated by humans, as follows: * Human impact on the enviro ...
and non-anthropogenic sources of this gas to the atmosphere. Some carbonyl sulfide that is transported into the stratospheric sulfate layer is oxidized to sulfuric acid. Sulfuric acid forms particulate which affects energy balance due to light scattering. The long atmospheric lifetime of COS makes it the major source of stratospheric sulfate, though
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
from volcanic activity can be significant too. Carbonyl sulfide is also removed from the atmosphere by terrestrial vegetation by enzymes associated with the uptake of carbon dioxide during photosynthesis, and by hydrolysis in ocean waters. Loss processes, such as these, limit the persistence (or lifetime) of a molecule of COS in the atmosphere to a few years. The largest man-made sources of carbonyl sulfide release include its primary use as a chemical intermediate and as a byproduct of carbon disulfide production; however, it is also released from automobiles and their tire wear, coal-fired power plants, coking ovens,
biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...
combustion, fish processing, combustion of refuse and plastics, petroleum manufacture, and manufacture of synthetic fibers, starch, and rubber. The average total worldwide release of carbonyl sulfide to the atmosphere has been estimated at about 3 million tons per year, of which less than one third was related to human activity. It is also a significant sulfur-containing impurity in many
fuel gas Fuel gas is one of a number of fuels that under ordinary conditions are gaseous. Most fuel gases are composed of hydrocarbons (such as methane and propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of energy that c ...
es such as synthesis gas, which are produced from sulfur-containing feedstocks. Carbonyl sulfide is present in
foodstuff Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin and contains essential nutrients such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is in ...
s, such as
cheese Cheese is a type of dairy product produced in a range of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk (usually the milk of cows, buffalo, goats or sheep). During prod ...
and prepared
vegetable Vegetables are edible parts of plants that are consumed by humans or other animals as food. This original meaning is still commonly used, and is applied to plants collectively to refer to all edible plant matter, including edible flower, flo ...
s of the cabbage family. Traces of COS are naturally present in
grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached husk, hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and ...
s and
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
s in the range of 0.05–0.1 mg/kg. Carbonyl sulfide has been observed in the interstellar medium (see also List of molecules in interstellar space), in comet 67P and in the atmosphere of Venus, where, because of the difficulty of producing COS inorganically, it is considered a possible indicator of life.


Reactions and applications

Carbonyl sulfide is used as an intermediate in the production of thiocarbamate herbicides. The hydrolysis of carbonyl sulfide is promoted by chromium-based catalysts: : This conversion is catalyzed in solution by carbonic anhydrase enzymes in plants and mammals. Because of this chemistry, the release of carbonyl sulfide from small organic molecules has been identified as a strategy for delivering hydrogen sulfide, which is gaseous signaling molecule. This compound is found to catalyze the formation of peptides from
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
s. This finding is an extension of the Miller–Urey experiment, and it is suggested that carbonyl sulfide played a significant role in the
origin of life Abiogenesis is the natural process by which life arises from abiotic component, non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to organism, living entities on ...
. In ecosystem science, are increasingly being used to describe the rate of
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
.


Synthesis

Carbonyl sulfide was first described in 1841, but was apparently mischaracterized as a mixture of carbon dioxide and
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
. Carl von Than first characterized the substance in 1867. It forms when
carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
reacts with molten sulfur: : This reaction reverses above . A laboratory synthesis entails the reaction
potassium thiocyanate Potassium thiocyanate is the chemical compound with the molecular formula KSCN. It is an important salt of the thiocyanate anion, one of the pseudohalides. The compound has a low melting point relative to most other inorganic salts. Uses Ch ...
and
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
: : The resulting gas contains significant amounts of byproducts and requires purification. Hydrolysis of isothiocyanates in hydrochloric acid solution also affords COS.


Toxicity

Carbonyl sulfide has the "rotten egg" odor characteristic of sulfides, although some sources suggest that the associated odor is due to impurities, and not present in the pure compound.CDC, ''Hydrogen Sulfide and Carbonyl Sulfide''
4. Chemical and Physical Information
p. 139. Retrieved 20 April 2025.
The detectability threshold is estimated at 135μg/m^3. As of 1994, limited information existed on the acute toxicity of carbonyl sulfide in humans and in animals. High concentrations (above 1000 ppm) can cause sudden collapse, convulsions, and death from respiratory paralysis. Occasional fatalities have been reported, practically without local irritation or olfactory warning. In tests with rats, 50% animals died when exposed to of COS for 90 minutes, or at for 9 minutes. Limited studies with laboratory animals also suggest that continued inhalation of low concentrations (around 50 ppm for up to 12 weeks) does not affect the lungs or the heart. Carbonyl sulfide is a potential alternative fumigant to
methyl bromide Bromomethane, commonly known as methyl bromide, is an organobromine compound with chemical formula, formula Carbon, CHydrogen, H3Bromine, Br. This colorless, odorless, nonflammable gas is Bromine cycle, produced both industrially and biologically ...
and
phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
. In some cases, however, residues on the grain result in flavours that are unacceptable to consumers, such as in barley used for brewing.


References


Further reading

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External links


Carbonyl sulfide and origins of life

Carbonyl sulfide as a potential fumigant

Carbonyl sulfide in the atmosphere
{{DEFAULTSORT:Carbonyl Sulfide Inorganic carbon compounds Inorganic sulfur compounds Oxides Sulfides