Editing Sulfur monoxide

{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 470474056
| ImageFile2 = Sulfur-monoxide-3D-balls.png
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageSize2 = 121
| ImageName2 = Ball and stick model of sulfur monoxide
| ImageFileL1 = Sulfur monoxide.svg
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageNameL1 = Skeletal formula of sulfur monoxide
| ImageFileR1 = Sulfur-monoxide-3D-vdW.png
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageNameR1 = Spacefill model of sulfur monoxide
| IUPACName = Sulfur monoxide{{Citation needed|date = July 2011}}
| SystematicName = Oxidosulfur<ref>{{cite web|url = https://www.ebi.ac.uk/chebi/searchId.do?chebiId=45822|title = sulfur monoxide (CHEBI:45822)|work = Chemical Entities of Biological Interest|location = UK|publisher = European Bioinformatics Institute}}</ref>
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|changed|??}}
| CASNo = 13827-32-2
| PubChem = 114845
| ChemSpiderID = 102805
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| MeSHName = sulfur+monoxide
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 45822
| ChEMBL = 1236102
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| Beilstein = 7577656
| Gmelin = 666
| SMILES = O=S
| StdInChI = 1S/OS/c1-2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/OS/c1-2
| StdInChIKey = XTQHKBHJIVJGKJ-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = XTQHKBHJIVJGKJ-UHFFFAOYAK
}}
|Section2={{Chembox Properties
| Formula = {{Chem|S|O}}
| MolarMass = 48.064 g mol<sup>−1</sup>
| Appearance = Colourless gas
| Solubility = Reacts
| LogP = 0.155
}}
|Section3={{Chembox Thermochemistry
| DeltaHf = 5.01 kJ mol<sup>−1</sup>
| Entropy = 221.94 J K<sup>−1</sup> mol<sup>−1</sup>
}}
|Section5={{Chembox Related
| OtherCompounds = [[Triplet oxygen]] <br /> [[Disulfur]]
}}
}}

'''Sulfur monoxide''' is an [[inorganic compound]] with [[chemical formula|formula]] {{chem2|auto=1|SO}}. It is only found as a dilute gas phase.  When concentrated or condensed, it converts to S<sub>2</sub>O<sub>2</sub> ([[disulfur dioxide]]). It has been detected in space but is rarely encountered intact otherwise.

==Structure and bonding==
The SO molecule has a triplet ground state similar to [[Dioxygen|O<sub>2</sub>]] and [[Disulfur|S<sub>2</sub>]], that is, each molecule has two unpaired electrons.<ref name = greenwood>{{Greenwood&Earnshaw}}</ref> The S−O [[bond length]] of 148.1&nbsp;pm is similar to that found in [[lower sulfur oxides]] (e.g. S<sub>8</sub>O, S−O = 148&nbsp;pm) but is longer than the S−O bond in gaseous [[disulfur monoxide|S<sub>2</sub>O]] (146&nbsp;pm), [[sulfur dioxide|SO<sub>2</sub>]] (143.1&nbsp;pm) and [[sulfur trioxide|SO<sub>3</sub>]] (142&nbsp;pm).<ref name = greenwood />

The molecule is excited with [[near infrared]] radiation to the singlet state (with no unpaired electrons). The singlet state is believed to be more reactive than the ground triplet state, in the same way that [[singlet oxygen]] is more reactive than [[triplet oxygen]].<ref>{{cite journal|title=Near-Infrared-Light-Induced Reaction of Singlet SO with Allene and Dimethylacetylene in a Rare Gas Matrix. Infrared Spectra of Two Novel Episulfoxides|last1=Salama|first1=F.|last2=Frei|first2=H. J.|journal=Journal of Physical Chemistry|date=1989|volume=93|pages=1285–1292|doi=10.1021/j100341a023}}</ref>

==Production and reactions==
The SO molecule is thermodynamically unstable, converting initially to [[disulfur dioxide|S<sub>2</sub>O<sub>2</sub>]].<ref name = greenwood/> Consequently controlled syntheses typically do not detect the presence of SO proper, but instead the reaction of a [[chemical trap]] or the terminal decomposition products of S<sub>2</sub>O<sub>2</sub> ([[sulfur]] and [[sulfur dioxide]]).  

Production of SO as a reagent in organic syntheses has centred on using compounds that "extrude" SO. Examples include the decomposition of the relatively simple molecule [[ethylene episulfoxide]]:<ref>{{cite journal|title=Sulfur Monoxide Chemistry. The Nature of SO from Thiirane Oxide and the Mechanism of Its Reaction with Dienes|last1=Chao|first1=P.|last2=Lemal|first2=D. M.|journal=Journal of the American Chemical Society|volume=95|issue=3|date=1973|page=920|doi=10.1021/ja00784a049}}</ref> 
:C<sub>2</sub>H<sub>4</sub>SO  → C<sub>2</sub>H<sub>4</sub> + SO
Yields directly from an episulfoxide are poor, and improve only moderately when the carbons are sterically shielded.<ref>{{cite journal|doi=10.1080/10426509708545509|journal=Phosphorus, Sulfur, and Silicon|year=1997|volume=120|page=53|publisher=Gordon & Breach|location=Amsterdam, NL|title=The sulfur diatomics|first=David&nbsp;N.|last=Harpp}}</ref>  A much better approach decomposes a diaryl cyclic trisulfide oxide, C<sub>10</sub>H<sub>6</sub>S<sub>3</sub>O, produced from [[thionyl chloride]] and the di[[thiol]].<ref>{{cite journal|doi = 10.1021/ol016678g|pmid = 11678709|title = A Novel Recyclable Sulfur Monoxide Transfer Reagent|journal = Organic Letters|volume = 3|issue = 22|pages = 3565–3568|year = 2001|last1 = Grainger|first1 = R. S.|last2 = Procopio|first2 = A.|last3 = Steed|first3 = J. W.}}</ref>

SO inserts into [[alkenes]], [[alkynes]] and [[diene]]s producing [[thiiranes]], molecules with three-membered rings containing sulfur.<ref>{{cite journal|title=[1+2] Cycloadditions of Sulfur Monoxide (SO) to Alkenes and Alkynes and [1+4]Cycloadditions to Dienes (Polyenes). Generation and Reactions of Singlet SO?|first1=J.|last1=Nakayama|first2=Y.|last2=Tajima|last3=Piao|first3=X.-H.|first4=Y.|last4=Sugihara|journal=Journal of the American Chemical Society|date=2007|volume=129|issue=23|pages=7250–7251|doi=10.1021/ja072044e|pmid=17506566}}</ref>

Sulfur monoxide may form transiently during the metallic reduction of [[thionyl bromide]].<ref name=Sulf>{{cite book|title=Sulfur in Organic and Inorganic Chemistry|volume=1|editor-first=Alexander|editor-last=Senning|year=1971|publisher=Marcel Dekker|location=New York|lccn=70-154612|isbn=0-8247-1615-9|first=Philip&nbsp;S.|last=Magee|chapter=The Sulfur&ndash;Bromine Bond|pages=271–276}}</ref>  

===Generation under extreme conditions===
In the laboratory, sulfur monoxide can be produced by treating [[sulfur dioxide]] with sulfur vapor in a [[glow discharge]].<ref name = greenwood /> It has been detected in single-bubble [[sonoluminescence]] of concentrated [[sulfuric acid]] containing some dissolved [[noble gas]].<ref>{{cite journal|title=The temperatures of single-bubble sonoluminescence (A)|last1=Suslick|first1=K. S.|last2=Flannigan|first2=D. J.|journal=The Journal of the Acoustical Society of America|date=2004|volume=116|issue=4|page=2540|doi=10.1121/1.4785135|bibcode=2004ASAJ..116.2540S}}</ref>

Benner and Stedman developed a [[chemiluminescence]] detector for sulfur via the reaction between sulfur monoxide and [[ozone]]:<ref>{{cite journal|title=Chemical Mechanism and Efficiency of the Sulfur Chemiluminescence Detector|last1=Benner|first1=R. L.|last2=Stedman|first2=D. H.|journal=Applied Spectroscopy|volume=48|issue=7|date=1994|pages=848–851|doi=10.1366/0003702944029901|bibcode=1994ApSpe..48..848B|s2cid=98849015}}</ref>
:SO + O<sub>3</sub> →  SO<sub>2</sub>* + O<sub>2</sub>
:SO<sub>2</sub>* →  SO<sub>2</sub> + [[photon|h''ν'']]
{{small|(* indicates an [[excited state]])}}

==Occurrence==

===Ligand for transition metals===
As a [[ligand]] SO can bond in a number different ways:<ref>{{cite journal|last=Schenk|first=W. A.|title=Sulfur Oxides as Ligands in Coordination Compounds. Angewandte Chemie International Edition in English|year=1987|volume=26|pages=98–109|doi=10.1002/anie.198700981}}</ref><ref>{{cite encyclopedia|entry=Sulfur: Inorganic Chemistry|last=Woollins|first=J. D.|encyclopedia=Encyclopedia of Inorganic Chemistry|date=1995|publisher=John Wiley and Sons|isbn=0-471-93620-0}}</ref>
*a terminal ligand, with a bent M−O−S arrangement, for example with [[titanium oxyfluoride]]<ref>{{cite journal |last1=Wei |first1=R. |last2=Chen |first2=X. |last3=Gong |first3=Y. |title=End-On Oxygen-Bound Sulfur Monoxide Complex of Titanium Oxyfluoride |journal=Inorganic Chemistry |date=2019 |volume=58 |issue=17 |pages=11801–11806 |doi=10.1021/acs.inorgchem.9b01880|pmid=31441297 |s2cid=201617509 }}</ref>
*a terminal ligand, with a bent M−S−O arrangement, analogous to bent [[nitrosyl]]
*[[Bridging ligand|bridging]] across two or three metal centres (via sulfur), as in Fe<sub>3</sub>(''μ''<sup>3</sup>-S)(''μ''<sup>3</sup>-SO)(CO)<sub>9</sub>
*[[Hapticity|''η''<sup>2</sup>]] sideways-on (d–π interaction) with [[vanadium]], [[niobium]], and [[tantalum]].<ref>{{cite journal|title=Side-On Sulfur Monoxide Complexes of Tantalum, Niobium, and Vanadium Oxyfluorides|journal=Inorganic Chemistry|first1=R.|last1=Wei|first2=X.|last2=Chen|first3=Y. |last3=Gong|year=2019|volume= 58|issue=6|pages=3807–3814|doi=10.1021/acs.inorgchem.8b03411|pmid=30707575|s2cid=73438027}}</ref>

===Astrochemistry===
Sulfur monoxide has been detected around [[Io (moon)|Io]], one of [[Jupiter]]'s moons, both in the atmosphere<ref>{{cite journal|title=Io's atmosphere: Not yet understood|last=Lellouch|first=E.|date=1996|journal=Icarus|volume=124|page=1–21|doi=10.1006/icar.1996.0186}}</ref> and in the [[Plasma (physics)|plasma]] [[torus]].<ref>{{cite journal|title=Detection of SO in Io's Exosphere|last1=Russell|first1=C. T.|last2=Kivelson|first2=M. G.|journal=Science|date=2000|volume=287|issue=5460|pages=1998–1999|doi=10.1126/science.287.5460.1998|pmid=10720321|bibcode=2000Sci...287.1998R}}</ref> It has also been found in the atmosphere of [[Venus]],<ref>{{cite journal|title=International Ultraviolet Explorer observations of Venus SO<sub>2</sub> and SO|last1=Na|first1=C. Y.|last2=Esposito|first2=L. W.|last3=Skinner|first3=T. E.|journal=Journal of Geophysical Research|volume=95|date=1990|pages=7485–7491|doi=10.1029/JD095iD06p07485|bibcode=1990JGR....95.7485N}}</ref> in [[Comet Hale–Bopp]],<ref>{{cite journal|title=New Molecular Species in Comet C/1995 O1 (Hale–Bopp) Observed with the Caltech S submillimeter Observatory|first1=D. C.|last1=Lis|first2=D. M.|last2=Mehringer|first3=D.|last3=Benford|first4=M.|last4=Gardner|first5=T. G.|last5=Phillips|first6=D.|last6=Bockelée-Morvan|author6-link=Dominique Bockelée-Morvan|first7=N.|last7=Biver|first8=P.|last8=Colom|first9=J.|last9=Crovisier|first10=D.|last10=Despois|first11=H.|last11=Rauer|journal=Earth, Moon, and Planets|volume=78|issue=1–3|date=1997|pages=13–20|doi=10.1023/A:1006281802554|bibcode=1997EM&P...78...13L|s2cid=51862359}}</ref> in [[67P/Churyumov–Gerasimenko]],<ref>{{cite web | url=https://sciencejournals.ru/view-article/?j=astvest&y=2020&v=54&n=2&a=AstVest2002002Dorofeeva | title=Астрономический вестник. T. 54, Номер 2, 2020 }}</ref> and in the [[interstellar medium]].<ref>{{cite journal|title=Observations of interstellar sulfur monoxide|last1=Gottlieb|first1=C. A.|last2=Gottlieb|first2=E. W.|last3=Litvak|first3=M. M.|last4=Ball|first4=J. A.|last5=Pennfield|first5=H.|journal=Astrophysical Journal|volume=1|issue=219|date=1978|pages=77–94|doi=10.1086/155757|bibcode=1978ApJ...219...77G}}</ref>

On [[Io (moon)|Io]], SO is thought to be produced both by [[Volcanism on Io|volcanic]] and [[photochemistry|photochemical]] routes. The principal photochemical reactions are proposed as follows:<ref>{{cite journal|title=Photochemistry of a Volcanically Driven Atmosphere on Io: Sulfur and Oxygen Species from a Pele-Type Eruption|last1=Moses|first1=J. I.|last2=Zolotov|first2=M. Y.|last3=Fegley|first3=B.|journal=Icarus|volume=156|pages=76–106|date=2002|issue=1|doi=10.1006/icar.2001.6758|bibcode=2002Icar..156...76M}}</ref>
: O  +  S<sub>2</sub>  →  S  +  SO
: SO<sub>2</sub>  → SO  +  O

Sulfur monoxide has been found in [[NML Cygni]].<ref name="Marvel1996">{{cite book|first=Kevin|last=Marvel|title=The Circumstellar Environment of Evolved Stars As Revealed by Studies of Circumstellar Water Masers|chapter-url=https://books.google.com/books?id=wwx1Gj5wR5QC&pg=PR182|access-date=23 August 2012|date=1996|publisher=Universal Publishers|isbn=978-1-58112-061-5|pages=182–212|chapter=NML Cygni}}</ref>

===Biological chemistry===
Sulfur monoxide may have some biological activity. The formation of transient SO in the [[coronary artery]] of [[pig]]s has been inferred from the reaction products, [[carbonyl sulfide]] and [[sulfur dioxide]].<ref>{{cite journal|title=Identification of carbonyl sulfide and sulfur dioxide in porcine coronary artery by gas chromatography/mass spectrometry, possible relevance to EDHF|last1=Balazy|first1=M.|last2=Abu-Yousef|first2=I. A.|last3=Harpp|first3=D. N.|last4=Park|first4=J.|journal=Biochemical and Biophysical Research Communications|date=2003|volume=311|issue=3|pages=728–734|doi=10.1016/j.bbrc.2003.10.055|pmid=14623333}}</ref>

==Safety measures==
Because of sulfur monoxide's rare occurrence in our atmosphere and poor stability, it is difficult to fully determine its hazards. But when condensed and compacted, it forms [[disulfur dioxide]], which is relatively toxic and corrosive. This compound is also highly flammable (similar flammability to [[methane]]) and when burned produces [[sulfur dioxide]], a poisonous gas.

== Sulfur monoxide dication ==
[[Sulfur dioxide]] SO<sub>2</sub> in presence of [[hexamethylbenzene]] C<sub>6</sub>(CH<sub>3</sub>)<sub>6</sub> can be protonated under [[superacid]]ic conditions ([[fluoroarsenic acid|HF·AsF<sub>5</sub>]]) to give the non-rigid [[Pi complex|π-complex]] C<sub>6</sub>(CH<sub>3</sub>)<sub>6</sub>SO<sup>2+</sup>. The SO<sup>2+</sup> moiety can essentially move barrierless over the [[benzene ring]]. The S−O bond length is 142.4(2)&nbsp;pm.<ref>{{cite journal|last1=Malischewski|first1=Moritz|last2=Seppelt|first2=Konrad|date=2017|title=Isolation and Characterization of a Non-Rigid Hexamethylbenzene-SO<sup>2+</sup> Complex|journal=Angewandte Chemie International Edition|language=en|volume=56|issue=52|pages=16495–16497|doi=10.1002/anie.201708552|pmid=29084371|s2cid=27260554 |issn=1433-7851|url=https://hal.sorbonne-universite.fr/hal-01730776/file/so_angew_sans%20marque.pdf}}</ref>

: C<sub>6</sub>(CH<sub>3</sub>)<sub>6</sub> + SO<sub>2</sub> + 3&nbsp;HF·AsF<sub>5</sub> → [C<sub>6</sub>(CH<sub>3</sub>)<sub>6</sub>SO][AsF<sub>6</sub>]<sub>2</sub> + [H<sub>3</sub>O][AsF<sub>6</sub>]

== Disulfur dioxide ==
[[File:Disulfur-dioxide-2D-dimensions.png|thumb|right|150px|The structure of disulfur dioxide, S<sub>2</sub>O<sub>2</sub>]]
[[File:Disulfur-dioxide-3D-vdW-A.png|thumb|right|150px|A [[space-filling model]] of the disulfur dioxide molecule]]
{{main|Disulfur dioxide}}
SO converts to disulfur dioxide (S<sub>2</sub>O<sub>2</sub>).<ref name =lovas>{{cite journal|title=Spectroscopic studies of the SO<sub>2</sub> discharge system. II. Microwave spectrum of the SO dimer|last1=Lovas|first1=F. J.|last2=Tiemann|first2=E.|last3=Johnson|first3=D. R.|journal=The Journal of Chemical Physics|date=1974|volume=60|issue=12|pages=5005–5010|doi=10.1063/1.1681015|bibcode=1974JChPh..60.5005L}}</ref> Disulfur dioxide is a planar molecule with ''C''<sub>2v</sub> [[symmetry group|symmetry]]. The S−O bond length is 145.8&nbsp;pm, shorter than in the monomer, and the S−S bond length is 202.45&nbsp;pm. The O−S−S angle is 112.7°.  S<sub>2</sub>O<sub>2</sub> has a dipole moment of 3.17&nbsp;[[debye (unit)|D]].<ref name = lovas />

==References==
{{reflist|30em}}
{{Oxides}}
{{Molecules detected in outer space}}
{{Authority control}}

{{DEFAULTSORT:Sulfur Monoxide}}
[[Category:Gases]]
[[Category:Interchalcogens]]
[[Category:Sulfur oxides]]
[[Category:Sulfur(II) compounds]]
[[Category:Diatomic molecules]]