Organosulfur compounds are
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
s that contain
sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g.,
saccharin
Saccharin (''aka'' saccharine, Sodium sacchari) is an artificial sweetener with effectively no nutritional value. It is about 550 times as sweet as sucrose but has a bitter or metallic aftertaste, especially at high concentrations. Saccharin is ...
. Nature abounds with organosulfur compounds—sulfur is vital for life. Of the 20 common
amino acids, two (
cysteine and
methionine) are organosulfur compounds, and the antibiotics
penicillin and
sulfa drugs both contain sulfur. While sulfur-containing antibiotics save many lives,
sulfur mustard is a deadly chemical warfare agent. Fossil fuels,
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
,
petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
, and
natural gas
Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
, which are derived from ancient organisms, necessarily contain organosulfur compounds,
the removal of which is a
major focus of
oil refineries.
Sulfur shares the
chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
group with
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
,
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
, and
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
, and it is expected that organosulfur compounds have similarities with carbon–oxygen, carbon–selenium, and carbon–tellurium compounds.
A classical
chemical test for the detection of sulfur compounds is the
Carius halogen method.
Classes
Organosulfur compounds can be classified according to the sulfur-containing
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
s, which are listed (approximately) in decreasing order of their occurrence.
Image:R-allicin-2D-skeletal.svg, Allicin, the active flavor compound in crushed garlic
Image:Cysteine.svg, (''R'')- Cysteine, an amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
containing a thiol group
Image:Methionin - Methionine.svg, Methionine, an amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
containing a sulfide
Image:Diphenyl disulfide.svg, Diphenyl disulfide
Diphenyl disulfide is the chemical compound with the formula (C6H5S)2. This colorless crystalline material is often abbreviated Ph2S2. It is one of the more commonly encountered organic disulfides in organic synthesis. Minor contamination by thiop ...
, a representative disulfide
Image:Dibenzothiophen - Dibenzothiophene.svg, Dibenzothiophene
Dibenzothiophene (DBT, diphenylene sulfide) is the organosulfur compound consisting of two benzene rings fused to a central thiophene ring. It is a colourless solid that is chemically somewhat similar to anthracene. This tricyclic heterocycle, ...
, a component of crude oil
Image:Perfluorooctanesulfonic acid structure.svg, Perfluorooctanesulfonic acid
Perfluorooctanesulfonic acid (PFOS) (conjugate base perfluorooctanesulfonate) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group and thus a perfluorosulfonic acid. It is an anthropogenic (man-ma ...
, a controversial surfactant
Image:Lipoic_acid.svg, Lipoic acid, an essential cofactor of four mitochondrial enzyme complexes.
Image:Penicillin core.svg, Penicillin core structure, where "R" is the variable group.
image:Sulfanilamide-skeletal.svg, Sulfanilamide, a sulfonamide antibacterial
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
, called a sulfa drug.
Image:Sulfur-mustard-2D-skeletal.svg, Sulfur mustard, a type of sulfide used as a chemical warfare agent
A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...
.
Image:MartinSulfurane.svg, Martin's sulfurane with a see-saw structure, like that of SF4
Sulfides
Sulfides, formerly known as thioethers, are characterized by C−S−C
bonds Relative to C−C bonds, C−S bonds are both longer, because sulfur atoms are larger than carbon atoms, and about 10% weaker. Representative
bond length
In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...
s in sulfur compounds are 183
pm for the S−C single bond in
methanethiol
Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. It is a natural substance found in the blood, brain and feces of animals (including humans ...
and 173 pm in
thiophene. The C−S
bond dissociation energy
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical ...
for thiomethane is 89 kcal/mol (370 kJ/mol) compared to methane's 100 kcal/mol (420 kJ/mol) and when hydrogen is replaced by a methyl group the energy decreases to 73 kcal/mol (305 kJ/mol). The single
carbon to oxygen bond is shorter than that of the C−C bond. The
bond dissociation energies for
dimethyl sulfide and
dimethyl ether are respectively 73 and 77 kcal/mol (305 and 322 kJ/mol).
Sulfides are typically prepared by
alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecti ...
of thiols. They can also be prepared via the
Pummerer rearrangement
The Pummerer rearrangement is an organic reaction whereby an alkyl sulfoxide rearranges to an α- acyloxy–thioether (mono thioacetal-ester) in the presence of acetic anhydride.
The stoichiometry of the reaction is:
:RS(O)CHR'2 + Ac2O → ...
. In one
named reaction A name reaction is a chemical reaction named after its discoverers or developers. Among the tens of thousands of organic reactions that are known, hundreds of such reactions are well-known enough to be named after people. Well-known examples include ...
called the
Ferrario reaction phenyl ether is converted to ''phenoxathiin'' by action of elemental sulfur and
aluminium chloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
.
:
Thioacetal
In organosulfur chemistry, thioacetals are the sulfur (''thio-'') analogues of acetals (). There are two classes: the less-common monothioacetals, with the formula , and the dithioacetals, with the formula (symmetric dithioacetals) or (asym ...
s and
thioketal
In organosulfur chemistry, a thioketal is the sulfur analogue of a ketal (), with one of the oxygen replaced by sulfur (as implied by the ''thio-'' prefix), giving the structure . A dithioketal has ''both'' oxygens replaced by sulfur ().
Thio ...
s feature C−S−C−S−C bond sequence. They represent a subclass of sulfides. The thioacetals are useful in "
umpolung
In organic chemistry, umpolung () or polarity inversion is the chemical modification of a functional group with the aim of the reversal of polarity of that group. This modification allows secondary reactions of this functional group that would ot ...
" of carbonyl groups. Thioacetals and thioketals can also be used to protect a carbonyl group in organic syntheses.
The above classes of sulfur compounds also exist in saturated and unsaturated
heterocyclic
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...
structures, often in combination with other
heteroatoms, as illustrated by
thiirane
Thiirane, more commonly known as ethylene sulfide, is the cyclic chemical compound with the formula C2H4S. It is the smallest sulfur-containing heterocycle and the simplest episulfide. Like many organosulfur compounds, this species has a highly ...
s,
thiirene
Thiirene is an organosulfur compound with the formula C2H2S. It can be viewed as a derivative of cyclopropene, but with the methylene group replaced by sulfur. It is antiaromatic and very labile.
Thiirenes and derivatives
No thiirene has bee ...
s,
thietanes,
thiete
Thiete is a heterocyclic compound containing an unsaturated four-membered ring with three carbon atoms and one sulfur atom. It is more commonly encountered not on its own, but in anellated derivatives, several of which have been synthesized. Thi ...
s,
dithietane
Dithietanes are saturated heterocyclic compounds that contain two divalent sulfur atoms and two sp3-hybridized carbon centers. Two isomers are possible for this class of organosulfur compounds:
1,2-Dithietanes
1,2-dithietanes, 4-membered rings ...
s,
thiolanes,
thiane
Thiane is a heterocyclic compound and an organosulfur compound
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, ...
s,
dithiane
A dithiane is a heterocyclic compound composed of a cyclohexane core structure wherein two methylene bridges (-- units) are replaced by sulfur centres. The three isomeric parent heterocycles are 1,2-dithiane, 1,3-dithiane and 1,4-dithiane.
1,3 ...
s,
thiepanes,
thiepines,
thiazole
Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular fo ...
s,
isothiazole
An isothiazole, or 1,2-thiazole, is a type of organic compound containing a five-membered aromatic ring that consists of three carbon atoms, one nitrogen atom, and one sulfur atom.''Heterocyclic Chemistry'', 3rd Edition, J.A. Joule, K. Mills, and ...
s, and
thiophenes, among others. The latter three compounds represent a special class of sulfur-containing heterocycles that are
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
. The
resonance stabilization
In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...
of
thiophene is 29 kcal/mol (121 kJ/mol) compared to 20 kcal/mol (84 kJ/mol) for the oxygen analogue
furan. The reason for this difference is the higher
electronegativity
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
for oxygen drawing away electrons to itself at the expense of the aromatic ring current. Yet as an aromatic
substituent the thio group is less electron-releasing than the alkoxy group.
Dibenzothiophene
Dibenzothiophene (DBT, diphenylene sulfide) is the organosulfur compound consisting of two benzene rings fused to a central thiophene ring. It is a colourless solid that is chemically somewhat similar to anthracene. This tricyclic heterocycle, ...
s (see drawing), tricyclic heterocycles consisting of two benzene rings fused to a central thiophene ring, occurs widely in heavier fractions of petroleum.
Thiols, disulfides, polysulfides
Thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
groups contain the functionality R−SH. Thiols are structurally similar to the
alcohol group, but these functionalities are very different in their chemical properties. Thiols are more
nucleophilic
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
, more acidic, and more readily oxidized. This acidity can differ by 5
p''K''a units.
The difference in
electronegativity
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
between sulfur (2.58) and hydrogen (2.20) is small and therefore
hydrogen bonding
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
in thiols is not prominent. Aliphatic thiols form
monolayers on
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
, which are topical in
nanotechnology.
Certain aromatic thiols can be accessed through a
Herz reaction.
Disulfides
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...
R−S−S−R with a covalent sulfur to sulfur bond are important for
crosslinking: in
biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
for the folding and stability of some proteins and in
polymer chemistry
Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are a ...
for the crosslinking of rubber.
Longer sulfur chains are also known, such as in the natural product
varacin which contains an unusual pentathiepin ring (5-sulfur chain cyclised onto a benzene ring).
Thioesters
Thioesters have general structure R−C(O)−S−R. They are related to regular esters (R−C(O)−O−R) but are more susceptible to hydrolysis and related reactions. Thioesters are prominent in biochemistry, especially in
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
synthesis.
Sulfoxides, sulfones and thiosulfinates
A
sulfoxide, R−S(O)−R, is the ''S''-oxide of a sulfide ("sulfide oxide"), a
sulfone
In organic chemistry, a sulfone is a organosulfur compound containing a sulfonyl () functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms and has a single bond to each of ...
, R−S(O)
2−R, is the ''S'',''S''-dioxide of a sulfide, a
thiosulfinate
In organosulfur chemistry, thiosulfinate is a functional group consisting of the linkage R-S(O)-S-R (R are organic substituents). Thiolsulfinates are also named as alkanethiosulfinic (or arenethiosulfinic) acid esters. They are the first member o ...
, R−S(O)−S−R, is the ''S''-oxide of a disulfide, and a thiosulfonate, R−S(O)
2−S−R, is the ''S'',''S''-dioxide of a disulfide. All of these compounds are well known with extensive chemistry, e.g.,
dimethyl sulfoxide,
dimethyl sulfone, and
allicin (see drawing).
Sulfimides, sulfoximides, sulfonediimines
Sulfimides (also called a sulfilimines) are sulfur–nitrogen compounds of structure R
2S=NR′, the nitrogen analog of sulfoxides. They are of interest in part due to their pharmacological properties. When two different R groups are attached to sulfur, sulfimides are chiral. Sulfimides form stable α-carbanions.
Sulfoximides (also called sulfoximines) are tetracoordinate sulfur–nitrogen compounds, isoelectronic with sulfones, in which one oxygen atom of the sulfone is replaced by a substituted nitrogen atom, e.g., R
2S(O)=NR′. When two different R groups are attached to sulfur, sulfoximides are chiral. Much of the interest in this class of compounds is derived from the discovery that methionine sulfoximide (methionine sulfoximine) is an inhibitor of
glutamine synthetase
Glutamine synthetase (GS) () is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:
Glutamate + ATP + NH3 → Glutamine + ADP + phosphate
Glutam ...
.
Sulfonediimines (also called sulfodiimines, sulfodiimides or sulfonediimides) are tetracoordinate sulfur–nitrogen compounds, isoelectronic with sulfones, in which both oxygen atoms of the sulfone are replaced by a substituted nitrogen atom, e.g., R
2S(=NR′)
2. They are of interest because of their biological activity and as building blocks for heterocycle synthesis.
''S''-Nitrosothiols
''S''-Nitrosothiols, also known as thionitrites, are compounds containing a nitroso group attached to the sulfur atom of a thiol, e.g. R−S−N=O. They have received considerable attention in biochemistry because they serve as donors of the nitrosonium ion, NO
+, and nitric oxide, NO, which may serve as signaling molecules in living systems, especially related to vasodilation.
Sulfur halides
A wide range of organosulfur compounds are known which contain one or more
halogen atom ("X" in the chemical formulas that follow) bonded to a single sulfur atom, e.g.:
sulfenyl halides, RSX;
sulfinyl halides, RS(O)X;
sulfonyl halides, RSO
2X; alkyl and arylsulfur trichlorides, RSCl
3 and trifluorides, RSF
3; and alkyl and arylsulfur pentafluorides, RSF
5. Less well known are dialkylsulfur tetrahalides, mainly represented by the tetrafluorides, e.g., R
2SF
4.
Thioketones, thioaldehydes, and related compounds
Compounds with
double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
s between carbon and sulfur are relatively uncommon, but include the important compounds
carbon disulfide
Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical n ...
,
carbonyl sulfide
Carbonyl sulfide is the chemical compound with the linear formula OCS. It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom. Carbonyl sulfide can be consi ...
, and
thiophosgene.
Thioketone
In organic chemistry, thioketones (; also known as thiones or thiocarbonyls) are organosulfur compounds related to conventional ketones in which the oxygen has been replaced by a sulfur. Instead of a structure of , thioketones have the structure ...
s (RC(=S)R′) are uncommon with alkyl substituents, but one example is
thiobenzophenone.
Thioaldehydes are rarer still, reflecting their lack of steric protection ("
thioformaldehyde" exists as a cyclic trimer).
Thioamide
A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure R–CS–NR′R″, where R, R′, and R″ are organic groups. They are analogous to amides but they exhibit greater multiple bond ch ...
s, with the formula R
1C(=S)N(R
2)R
3 are more common. They are typically prepared by the reaction of amides with
Lawesson's reagent.
Isothiocyanate
In organic chemistry, isothiocyanate is the functional group , formed by substituting the oxygen in the isocyanate group with a sulfur. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosi ...
s, with formula R−N=C=S, are found naturally. Vegetable foods with characteristic flavors due to isothiocyanates include
wasabi
Wasabi ( Japanese: , , or , ; ''Eutrema japonicum'' or ''Wasabia japonica'') or Japanese horseradish is a plant of the family Brassicaceae, which also includes horseradish and mustard in other genera. The plant is native to Japan and the Russi ...
,
horseradish
Horseradish (''Armoracia rusticana'', syn. ''Cochlearia armoracia'') is a perennial plant of the family Brassicaceae (which also includes mustard, wasabi, broccoli, cabbage, and radish). It is a root vegetable, cultivated and used worldwi ...
,
mustard
Mustard may refer to:
Food and plants
* Mustard (condiment), a paste or sauce made from mustard seeds used as a condiment
* Mustard plant, one of several plants, having seeds that are used for the condiment
** Mustard seed, seeds of the mustard p ...
,
radish
The radish (''Raphanus raphanistrum'' subsp. ''sativus'') is an edible root vegetable of the family Brassicaceae that was domesticated in Asia prior to Roman times.
Radishes are grown and consumed throughout the world, being mostly eaten raw ...
,
Brussels sprout
The Brussels sprout is a member of the Gemmifera cultivar group of cabbages (''Brassica oleracea''), grown for its edible buds. The leaf vegetables are typically 1.5–4.0 cm (0.6–1.6 in) in diameter and resemble miniature cabbages ...
s,
watercress
Watercress or yellowcress (''Nasturtium officinale'') is a species of aquatic flowering plant in the cabbage family Brassicaceae.
Watercress is a rapidly growing perennial plant native to Europe and Asia. It is one of the oldest known leaf v ...
,
nasturtiums, and
caper
''Capparis spinosa'', the caper bush, also called Flinders rose, is a perennial plant that bears rounded, fleshy leaves and large white to pinkish-white flowers.
The plant is best known for the edible flower buds (capers), used as a seasoning ...
s.
''S''-Oxides and ''S'',''S''-dioxides of thiocarbonyl compounds
The ''S''-oxides of thiocarbonyl compounds are known as thiocarbonyl ''S''-oxides: (R
2C=S=O, and thiocarbonyl ''S'',''S''-dioxides or
sulfene
Sulfene is an extremely reactive chemical compound with the formula H2C=SO2. It is the simplest member of the sulfenes, the group of compounds which are ''S'',''S''-dioxides of thioaldehydes and thioketones, and have the general formula R2C=SO2.
...
s, R
2C=SO
2). The thione ''S''-oxides have also been known as
sulfines, and while
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
considers this term obsolete, the name persists in the literature. These compounds are well known with extensive chemistry. Examples include
''syn''-propanethial-''S''-oxide and
sulfene
Sulfene is an extremely reactive chemical compound with the formula H2C=SO2. It is the simplest member of the sulfenes, the group of compounds which are ''S'',''S''-dioxides of thioaldehydes and thioketones, and have the general formula R2C=SO2.
...
.
Triple bonds between carbon and sulfur
Triple bonds between sulfur and carbon in sulfaalkynes are rare and can be found in
carbon monosulfide (CS) and have been suggested for the compounds F
3CCSF
3 and F
5SCSF
3. The compound HCSOH is also represented as having a formal triple bond.
Thiocarboxylic acids and thioamides
Thiocarboxylic acids (RC(O)SH) and dithiocarboxylic acids (RC(S)SH) are well known. They are structurally similar to carboxylic acids but more acidic. Thioamides are analogous to amides.
Sulfonic, sulfinic and sulfenic acids, esters, amides, and related compounds
Sulfonic acids have functionality R−S(=O)
2−OH. They are strong acids that are typically soluble in organic solvents. Sulfonic acids like
trifluoromethanesulfonic acid
Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF3SO3H. It is one of the strongest known acids. Triflic acid is mainly used in research as a catalyst for es ...
is a frequently used reagent in
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
.
Sulfinic acids have functionality R−S(O)−OH while
sulfenic acids have functionality R−S−OH. In the series sulfonic—sulfinic—sulfenic acids, both the acid strength and stability diminish in that order. Sulfonamides,
sulfinamides and
sulfenamides, with formulas R−SO
2NR′
2, R−S(O)NR′
2, and R−SNR′
2, respectively, each have a rich chemistry. For example,
sulfa drugs are sulfonamides derived from
aromatic sulfonation. Chiral sulfinamides are used in asymmetric synthesis, while sulfenamides are used extensively in the vulcanization process to assist cross-linking.
Thiocyanate
Thiocyanate (also known as rhodanide) is the anion . It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyr ...
s, R−S−CN, are related to sulfenyl halides and esters in terms of reactivity.
Sulfonium, oxosulfonium and related salts
A
sulfonium ion is a positively charged ion featuring three organic substituents attached to sulfur, with the formula
3S">3Ssup>+. Together with their negatively charged counterpart, the anion, the compounds are called sulfonium salts. An oxosulfonium ion is a positively charged ion featuring three organic substituents and an oxygen attached to sulfur, with the formula
3S=O">3S=Osup>+. Together with their negatively charged counterpart, the anion, the compounds are called oxosulfonium salts. Related species include alkoxysulfonium and chlorosulfonium ions,
2SOR">2SORsup>+ and
2SCl">2SClsup>+, respectively.
Sulfonium, oxosulfonium and thiocarbonyl ylides
Deprotonation of sulfonium and oxosulfonium salts affords
ylides, of structure R
2S
+−C
−−R′
2 and R
2S(O)
+−C
−−R′
2. While
sulfonium ylide An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms ...
s, for instance in the
Johnson–Corey–Chaykovsky reaction
The Johnson–Corey–Chaykovsky reaction (sometimes referred to as the Corey–Chaykovsky reaction or CCR) is a chemical reaction used in organic chemistry for the synthesis of epoxides, aziridines, and cyclopropanes. It was discovered in 1961 b ...
used to synthesize
epoxide
In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...
s, are sometimes drawn with a C=S double bond, e.g., R
2S=CR′
2, the ylidic carbon–sulfur bond is highly polarized and is better described as being ionic. Sulfonium ylides are key intermediates in the synthetically useful
Stevens rearrangement
The Stevens rearrangement in organic chemistry is an organic reaction converting quaternary ammonium salts and sulfonium salts to the corresponding amines or sulfides in presence of a strong base in a 1,2-rearrangement.
The reactants can b ...
. Thiocarbonyl ylides (RR′C=S
+−C
−−RR′) can form by ring-opening of
thiirane
Thiirane, more commonly known as ethylene sulfide, is the cyclic chemical compound with the formula C2H4S. It is the smallest sulfur-containing heterocycle and the simplest episulfide. Like many organosulfur compounds, this species has a highly ...
s, photocyclization of aryl vinyl sulfides, as well as by other processes.
Sulfuranes and persulfuranes
Sulfuranes are relatively specialized functional group that are
tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
Description
The combining capacity, or affinity of an ...
,
hypervalent
In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus pe ...
sulfur compounds, with the formula SR
4 and likewise persulfuranes are
hexavalent SR
6. All-carbon hexavalent complexes have been known for the heavier representatives of the
chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
group, for instance the compound hexamethylpertellurane (Te(Me)
6) was discovered in 1990 by reaction of tetramethyltellurium with
xenon difluoride to TeF
2(CH
3)
4 followed by reaction with
dimethylzinc. The sulfur analogue hexamethylpersulfurane (S(CH
3)
6) has been predicted to be stable but has not been synthesized yet.
The first ever all-carbon persulfurane actually synthesized in a laboratory has two
methyl and two
biphenyl
Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound that forms colorless crystals. Particularly in older literature, compounds containing the functional group consisting of biphenyl less one ...
ligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
s:
:
It is prepared from the corresponding sulfurane 1 with
xenon difluoride /
boron trifluoride in
acetonitrile to the sulfuranyl dication 2 followed by reaction with
methyllithium
Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in so ...
in
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
to (a stable) persulfurane 3 as the
cis isomer
Cis or cis- may refer to:
Places
* Cis, Trentino, in Italy
* In Poland:
** Cis, Świętokrzyskie Voivodeship, south-central
** Cis, Warmian-Masurian Voivodeship, north
Math, science and biology
* cis (mathematics) (cis(''θ'')), a trigonom ...
.
X-ray diffraction shows C−S
bond length
In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...
s ranging between 189 and 193 pm (longer than the standard bond length) with the central sulfur atom in a distorted
octahedral molecular geometry.
Computer simulation suggests that these bonds are very polar with the negative charges residing on carbon.
Naturally occurring organosulfur compounds
Not all organosulfur compounds are foul-smelling pollutants.
Penicillin and
cephalosporin are life-saving
antibiotics, derived from fungi.
Gliotoxin
Gliotoxin is a sulfur-containing mycotoxin that belongs to a class of naturally occurring 2,5-diketopiperazines produced by several species of fungi, especially those of marine origin. It is the most prominent member of the epipolythiopiperazi ...
is a sulfur-containing
mycotoxin
A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...
produced by several species of fungi under investigation as an
antiviral agent. Compounds like
allicin and
ajoene are responsible for the odor of
garlic, and
lenthionine contributes to the flavor of
shiitake mushrooms. Volatile organosulfur compounds also contribute subtle flavor characteristics to
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
, nuts,
cheddar cheese,
chocolate
Chocolate is a food made from roasted and ground cacao seed kernels that is available as a liquid, solid, or paste, either on its own or as a flavoring agent in other foods. Cacao has been consumed in some form since at least the Olmec civ ...
,
coffee
Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world.
Seeds of ...
, and tropical fruit flavors. Many of these natural products also have important medicinal properties such as preventing
platelet
Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby i ...
aggregation or fighting cancer.
In pollution
Most organic sulfur compounds in the environment are naturally occurring, as a consequence of the fact that sulfur is essential for life and two amino acids (cysteine and methionine) contain this element.
Some organosulfur compounds in the environment, are generated as minor by-products of industrial processes such as the manufacture of plastics and tires.
Selected smell-producing processes are organosulfur compounds produced by the coking of coal designed to drive out sulfurous compounds and other volatile impurities in order to produce 'clean carbon' (
coke), which is primarily used for steel production.
In fossil fuels
Odours occur as well in
chemical
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
processing of
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
or
crude oil into precursor chemicals (feedstocks) for downstream industrial uses (e.g.
plastics or pharmaceutical production) and the ubiquitous needs of petroleum distillation for
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
s,
diesel, and other grades of
fuel oils production.
Organosulfur compounds might be understood as aromatic contaminants that need to be removed from natural gas before commercial uses, from exhaust stacks and exhaust vents before discharge. In this latter context, organosulfur compounds may be said to account for the pollutants in sulfurous
acid rain, or equivalently, said to be pollutants within most common fossil fuels, especially
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
.
The most common organosulfur compound present in all petroleum fractions is
thiophene (C
4H
4S), a cyclic and aromatic liquid. In addition, the heavy fractions of oil contain
benzothiophene
Benzothiophene is an aromatic organic compound with a molecular formula C8H6S and an odor similar to naphthalene (mothballs). It occurs naturally as a constituent of petroleum-related deposits such as lignite tar. Benzothiophene has no househol ...
(C
8H
6S, thianaphtene) and
dibenzothiophene
Dibenzothiophene (DBT, diphenylene sulfide) is the organosulfur compound consisting of two benzene rings fused to a central thiophene ring. It is a colourless solid that is chemically somewhat similar to anthracene. This tricyclic heterocycle, ...
. Most of the last compounds are solids and smell like naphthalene. Many methylated, dimethyl, diethyl benzothiophene derivatives are present in diesel and fuel oils which make fuel oils very difficult to clean.
All these heterocyclic sulfides account for 200–500 ppm of natural fuel, the heavily substituted dibenzothiophenes remain after HDS and account for 10–20 ppm. These molecules are also found in coals and they must be eliminated before consumption.
Reduced molybdenum together with nickel is currently used to eliminate thiophenes from petroleum (HDS) due to its great affinity towards sulfur.
In addition tungsten together with nickel and cobalt is used for
hydrodesulfurization (HDS) in large refineries. The adsorption mechanism of thiophene to transition metals is proposed to occur through the π system, where the organosulfur compound lies almost parallel to the metal surface.
Many researchers focus their efforts in optimizing the oxidation state of the transition metals for HDS, like Cu(I) and Ag(II) which together with Pd(0) have proven to be more specific for π bonding with thiophenes of all kinds.
Basis for odor
Humans and other animals have an exquisitely sensitive sense of smell toward the
odor of low-valent organosulfur compounds such as thiols, sulfides, and disulfides. Malodorous volatile thiols are protein-degradation products found in putrid food, so sensitive identification of these compounds is crucial to avoiding intoxication. Low-valent volatile sulfur compounds are also found in areas where oxygen levels in the air are low, posing a risk of suffocation. It has been found that copper is required for the highly sensitive detection of certain volatile thiols and related organosulfur compounds by olfactory receptors in mice. Whether humans, too, require copper for sensitive detection of thiols is not yet known.
References
{{Authority control
Soil chemistry
Foul-smelling chemicals