Sulfanyl
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Sulfanyl (•), also known as the mercapto radical, hydrosulfide radical, or hydridosulfur, is a simple radical molecule consisting of one hydrogen and one sulfur atom. The radical appears in metabolism in organisms as H2S is detoxified. Sulfanyl is one of the top three sulfur-containing gasses in
gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...
s such as
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...
and is very likely to be found in
brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
s and cool stars. It was originally discovered by Margaret N. Lewis and John U. White at the
University of California The University of California (UC) is a public land-grant research university system in the U.S. state of California. The system is composed of the campuses at Berkeley, Davis, Irvine, Los Angeles, Merced, Riverside, San Diego, San Franci ...
in 1939. They observed molecular absorption bands around 325 nm belonging to the system designated by 2Σ+ ← 2Πi. They generated the radical by means of a radio frequency discharge in hydrogen sulfide. HS• is formed during the degradation of hydrogen sulfide in the atmosphere of the Earth. This may be a deliberate action to destroy odours or a natural phenomenon. The organic analogue of sulfanyl is
thiyl radical In chemistry, a thiyl radical has the formula RS, sometimes written RS• to emphasize that they are free radicals. R is typically an alkyl or aryl substituent. Because S–H bonds are about 20% weaker than C–H bonds, thiyl radicals are relativ ...
with the formula RS., where R =
alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
or
aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...
.


Natural occurrence

Absorption lines of sulfanyl in space were first detected in the
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
by Yamamura (2000) in a star R And. In the sun •SH was detected at several
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s: 326.0459, 327.5468, 328.9749, 330.0892 and 330.1112 nm. Sulfanyl has been detected in
interstellar gas In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
, and it is possibly present in comets. Various theoretical studies have examined HS• in atmospheres. In Earth's atmosphere HS• reacts with NO2 to make two products HSNO2 and HSONO. HSONO decomposes to HSO and NO. HS• also reacts with O2 and N2O. HS• can also react with Cl2 producing HSCl and a Cl• atom. HS• destroys
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
producing HSO• and oxygen. HS• is formed in the Earth's atmosphere by the reaction of HO•, the
hydroxyl radical The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals are produced from the ...
, on
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 ...
, carbon oxysulfide and hydrogen sulfide with side products of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and water. Photodissociation of hydrogen sulfide also produces the radical in air. In a planetary atmosphere that contains H2S, HS• will be formed if the temperature and pressure are high enough. The ratio of H2S and HS• is given by: :log(''X''/''X'') = −3.37 + 8785/''T'' + 0.5 log ''PT'' + 0.5 log ''X''H2 For a hydrogen dominated atmosphere in a gas giant or star: H2S has the same level as HS• at :\log P_T = 6.82 - 17570/T. At higher temperatures HS• breaks up into sulfur vapour and H2. The line of equal S and HS concentration follows the line :gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...
s or
brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
s.


Formation

Thermal decomposition of mercaptans, such as
ethyl mercaptan Ethanethiol, commonly known as ethyl mercaptan, is an organosulfur compound with the formula CH3CH2SH. is a colorless liquid with a distinct odor. Abbreviated EtSH, it consists of an ethyl group (Et), CH3CH2, attached to a thiol group, SH. Its s ...
yields •. The radical can be formed by the action of
ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
on hydrogen sulfide, which splits off a hydrogen atom. A
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
of 190 nm gives maximum absorption. In humans superoxide dismutase u-Znconverts the hydrosulfide ion (HS−) to •. This happens as the Cu2+ ion in the enzyme is converted to Cu+. Sulfide dehydrogenase as found in sulfur bacteria catalyses the oxidation of HS− to •, by removing a single electron. When sulfur minerals are leached with ferric ions HS• is formed in this way: :MS + Fe3+ + 2H+ → M2+ + Fe2+ + H2S•+ with the H2S•+ radical then passing a proton to water to make the HS• radical. M is a metal such as zinc or copper. This has potential for
bioleaching Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cyanide. Bioleaching is one of several applications within biohydrometallurgy and several ...
in metallic ore extraction. The
hydrosulfide ion Bisulfide (or bisulphide in British English) is an inorganic anion with the chemical formula HS− (also written as SH−). It contributes no color to bisulfide salts, and its salts may have a distinctive putrid smell. It is a strong base. Bisul ...
HS− can be oxidized to HS• with
cerium (IV) sulfate Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce( SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids th ...
.


Reactions

Being a radical, HS• is quite reactive. In water HS can react with O2 producing SO2− and H+. SO2− reacts further with O2 to make SO2 and
superoxide In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of t ...
O2−. In water HS• has an equilibrium with S− • and H+. The hydroxyl radical •OH combines with H2S to form HS• and water. Other reactions investigated by Tiee (1981) are HS• + ethylene, HS• + O2 → HO• + SO, and reactions with itself HS• + HS• → H2S2 or H2 and S. The disulfide can further react with HS• to make the disulfide radical HS–S• and H2S.


Properties

The ionization energy of HS is 10.4219 eV. The reduction potential to go to HS− is 0.92 eV. HS• in water can ionize to S•− and H+. The S•− can catalyze a cis-trans conversion in
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids includ ...
s. The interatomic distance between sulfur and hydrogen in the radical is 0.134 nm. HS• reacts with carboxylic acids to make
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 ...
(COS) and probably is the main source of this substance in the atmosphere of Earth.


Related molecules

HS—S• is called disufanyl with lengthening chains as trisulfanyl, tetrasulfanyl and pentasulfanyl HSSSSS•. S−* is termed sulfanidyl. HS+ is known as sulfanylium, and the common
hydrosulfide ion Bisulfide (or bisulphide in British English) is an inorganic anion with the chemical formula HS− (also written as SH−). It contributes no color to bisulfide salts, and its salts may have a distinctive putrid smell. It is a strong base. Bisul ...
HS− is also known as sulfanido for a ligand or sulfanide as an anion. Further down the periodic table, HSe• is known as selanyl, and HTe• is termed tellanyl.


References


External links


Mercapto radical
from NIST * * * Sulfur deuteride radical SD• microwave spectrum {{Hydrides by group Hydrides Sulfur compounds