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{{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}}
|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−1
| Appearance = Colourless gas
| Solubility = Reacts
| LogP = 0.155
}}
|Section3={{Chembox Thermochemistry
| DeltaHf = 5.01 kJ mol−1
| Entropy = 221.94 J K−1 mol−1
}}
|Section5={{Chembox Related
| OtherCompounds = Triplet oxygen
Disulfur
}}
}}
Sulfur monoxide is an inorganic compound with formula {{chem2|auto=1|SO}}. It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2 (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 O2 and S2, that is, each molecule has two unpaired electrons.{{Greenwood&Earnshaw}} The S−O bond length of 148.1 pm is similar to that found in lower sulfur oxides (e.g. S8O, S−O = 148 pm) but is longer than the S−O bond in gaseous S2O (146 pm), SO2 (143.1 pm) and SO3 (142 pm).
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.{{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}}
Production and reactions
The SO molecule is thermodynamically unstable, converting initially to S2O2. 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 S2O2 (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:{{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}}
:C2H4SO → C2H4 + SO
Yields directly from an episulfoxide are poor, and improve only moderately when the carbons are sterically shielded.{{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 N.|last=Harpp}} A much better approach decomposes a diaryl cyclic trisulfide oxide, C10H6S3O, produced from thionyl chloride and the dithiol.{{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.}}
SO inserts into alkenes, alkynes and dienes producing thiiranes, molecules with three-membered rings containing sulfur.{{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}}
Sulfur monoxide may form transiently during the metallic reduction of thionyl bromide.{{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 S.|last=Magee|chapter=The Sulfur–Bromine Bond|pages=271–276}}
=Generation under extreme conditions=
In the laboratory, sulfur monoxide can be produced by treating sulfur dioxide with sulfur vapor in a glow discharge. It has been detected in single-bubble sonoluminescence of concentrated sulfuric acid containing some dissolved noble gas.{{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}}
Benner and Stedman developed a chemiluminescence detector for sulfur via the reaction between sulfur monoxide and ozone:{{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}}
:SO + O3 → SO2* + O2
:SO2* → SO2 + hν
{{small|(* indicates an excited state)}}
Occurrence
=Ligand for transition metals=
As a ligand SO can bond in a number different ways:{{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}}{{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}}
- a terminal ligand, with a bent M−O−S arrangement, for example with titanium oxyfluoride{{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 }}
- a terminal ligand, with a bent M−S−O arrangement, analogous to bent nitrosyl
- bridging across two or three metal centres (via sulfur), as in Fe3(μ3-S)(μ3-SO)(CO)9
- η2 sideways-on (d–π interaction) with vanadium, niobium, and tantalum.{{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}}
=Astrochemistry=
Sulfur monoxide has been detected around Io, one of Jupiter's moons, both in the atmosphere{{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}} and in the plasma torus.{{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}} It has also been found in the atmosphere of Venus,{{cite journal|title=International Ultraviolet Explorer observations of Venus SO2 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}} in Comet Hale–Bopp,{{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}} in 67P/Churyumov–Gerasimenko,{{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 }} and in the interstellar medium.{{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}}
On Io, SO is thought to be produced both by volcanic and photochemical routes. The principal photochemical reactions are proposed as follows:{{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}}
: O + S2 → S + SO
: SO2 → SO + O
Sulfur monoxide has been found in NML Cygni.{{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}}
=Biological chemistry=
Sulfur monoxide may have some biological activity. The formation of transient SO in the coronary artery of pigs has been inferred from the reaction products, carbonyl sulfide and sulfur dioxide.{{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}}
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 SO2 in presence of hexamethylbenzene C6(CH3)6 can be protonated under superacidic conditions (HF·AsF5) to give the non-rigid π-complex C6(CH3)6SO2+. The SO2+ moiety can essentially move barrierless over the benzene ring. The S−O bond length is 142.4(2) pm.{{cite journal|last1=Malischewski|first1=Moritz|last2=Seppelt|first2=Konrad|date=2017|title=Isolation and Characterization of a Non-Rigid Hexamethylbenzene-SO2+ 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}}
: C6(CH3)6 + SO2 + 3 HF·AsF5 → [C6(CH3)6SO][AsF6]2 + [H3O][AsF6]
Disulfur dioxide
File:Disulfur-dioxide-2D-dimensions.png
File:Disulfur-dioxide-3D-vdW-A.png of the disulfur dioxide molecule]]
{{main|Disulfur dioxide}}
SO converts to disulfur dioxide (S2O2).{{cite journal|title=Spectroscopic studies of the SO2 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}} Disulfur dioxide is a planar molecule with C2v symmetry. The S−O bond length is 145.8 pm, shorter than in the monomer, and the S−S bond length is 202.45 pm. The O−S−S angle is 112.7°. S2O2 has a dipole moment of 3.17 D.
References
{{reflist|30em}}
{{Oxides}}
{{Molecules detected in outer space}}
{{Authority control}}
{{DEFAULTSORT:Sulfur Monoxide}}