Sulfanyl
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 HS is detoxified. Sulfanyl is one of the top three sulfur-containing gasses in gas giants such as Jupiter and is very likely to be found in brown dwarfs and cool stars. It was originally discovered by Margaret N. Lewis and John U. White at the University of California in 1939. They observed molecular absorption bands around 325 nm belonging to the system designated by Σ ←  Π. 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 with the formula RS, where R = alkyl or aryl. Natural occurrence. Absorption lines of sulfanyl in space were first detected in the infrared by Yamamura (2000) in a star R And. In the sun SH was detected at several ultraviolet wavelengths: 326.0459, 327.5468, 328.9749, 330.0892 and 330.1112 nm . Sulfanyl has been detected in interstellar gas, and it is possibly present in comets. Various theoretical studies have examined HS in atmospheres. In Earth's atmosphere HS reacts with NO to make two products HSNO and HSONO. HSONO decomposes to HSO and NO. HS also reacts with O and NO. HS can also react with Cl producing HSCl and a Cl atom. HS destroys ozone producing HSO and oxygen. HS is formed in the Earth's atmosphere by the reaction of HO, the hydroxyl radical, on carbon disulfide, carbon oxysulfide and hydrogen sulfide with side products of carbon dioxide and  water. Photodissociation of hydrogen sulfide also produces the radical in air. In a planetary atmosphere that contains HS, HS will be formed if the temperature and pressure are high enough. The ratio of HS and HS is given by: For a hydrogen dominated atmosphere in a gas giant or star: HS has the same level as HS at At higher temperatures HS breaks up into sulfur vapour and H. The line of equal S and HS concentration follows the line The lines of equal concentration cross at 1509 K and 1.51 Pa, with HS being left out of the mix  at lower temperatures and pressures. SH is expected to be the second or third most common sulfur containing gas in gas giants or brown dwarfs. Formation. Thermal decomposition of mercaptans, such as ethyl mercaptan yields . The radical can be formed by the action of ultraviolet radiation on hydrogen sulfide, which splits off a hydrogen atom. A wavelength of 190 nm gives maximum absorption. In humans superoxide dismutase [Cu-Zn] converts the hydrosulfide ion (HS) to . This happens as the Cu 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: with the HS 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 in metallic ore extraction. The hydrosulfide ion HS can be oxidized to HS with cerium (IV) sulfate. Reactions. Being a radical, HS is quite reactive. In water HS can react with O producing SO and H. SO reacts further with O to make SO and superoxide O. In water HS has  an equilibrium with S and H. The hydroxyl radical OH combines with HS to form HS and water. Other reactions investigated by Tiee (1981) are HS + ethylene, HS + O → HO + SO, and reactions with itself HS + HS → HS or H and S. The disulfide can further react with HS to make the disulfide radical HS–S and HS. 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 lipids. The interatomic distance between sulfur and hydrogen in the radical is 0.134 nm. HS reacts with carboxylic acids to make carbonyl sulfide (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 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.