Disulfur
{{Chembox
| Watchedfields = changed
| verifiedrevid = 450793307
| Name =
| ImageFile = Disulfur-2D-dimensions.png
| ImageFile1 = Disulfur-3D-balls.png
| ImageFile_Ref = {{Chemboximage|correct|??}}
| ImageName = Ball and stick model of disulfur molecule
| IUPACName = Disulfurebi.ac.uk/chebi/searchId.do?chebiId=29387
| SystematicName = Disulfene
| OtherNames = Diatomic sulfur
Sulfur dimer
Disulphur
| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 23550-45-0
| PubChem = 5460602
| ChemSpiderID = 4574100
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| Gmelin = 753
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 29387
| SMILES = S=S
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/S2/c1-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = MAHNFPMIPQKPPI-UHFFFAOYSA-N
}}
| Section2 = {{Chembox Properties
| S=2
| Dipole = 0 D
}}
| Section3 = {{Chembox Thermochemistry
| DeltaHf = 128.60 kJ mol−1
| Entropy = 228.17 J K−1 mol−1
| HeatCapacity = 32.51 kJ K−1 mol−1
}}
| Section4 = {{Chembox Related
| OtherCompounds = Triplet oxygen
}}
| Section5 =
| Section6 =
}}
Disulfur is the diatomic molecule with the formula S2.{{Cite book| last1 = Steudel | first1 = Ralf| last2 = Eckert | first2 = Bodo| chapter = Solid Sulfur Allotropes| doi = 10.1007/b12110 | title = Elemental Sulfur and Sulfur-Rich Compounds I | series = Topics in Current Chemistry | volume = 230 | pages = 58–68| year = 2003 | isbn = 978-3-540-40191-9 }} It is analogous to the dioxygen molecule but rarely occurs at room temperature. This violet gas is the dominant species in hot sulfur vapors. S2 is one of the minor components of the atmosphere of Io, which is predominantly composed of SO2.{{Cite journal | last1 = Lellouch | first1 = E.| doi = 10.1007/s11214-005-1957-z | title = Io's Atmosphere and Surface–Atmosphere Interactions | journal = Space Science Reviews | volume = 116 | issue = 1–2| pages = 211–224 | date=January 2005 |bibcode = 2005SSRv..116..211L | s2cid = 121867974}} The instability of S2 is usually described in the context of the double bond rule.
Synthesis
This violet gas is generated by heating sulfur and is the predominant species above 720 °C, comprising 80% of all vapor species at 530°C and 100 mm Hg, and 99% of the vapor at low pressure (1 mm Hg) at 730 °C.{{cite book |last1=Greenwood |first1=N. N. |author-link1=Norman Greenwood |last2=Earnshaw |first2=A. |year=1997 |title=Chemistry of the Elements |edition=2nd |publisher=Butterworth-Heinemann |isbn=978-0-08-037941-8}}
Disulfur can be produced when an atmosphere of COS is irradiated with UV light using a mercury photosensitizer or when CS2, H2S2, S2Cl2 or C2H4S, PSF3 or COS are irradiated.{{Cite journal | last1 = Tardif | first1 = Sylvie L.| last2 = Rys | first2 = Andrzej Z.| last3 = Abrams | first3 = Charles B.| last4 = Abu-Yousef | first4 = Imad A.| last5 = Lesté-Lasserre | first5 = Pierre B. F.| last6 = Schultz | first6 = Erwin K. V.| last7 = Harpp | first7 = David N.| doi = 10.1016/S0040-4020(97)00555-3 | title = Recent chemistry of the chalcogen diatomics | journal = Tetrahedron | volume = 53 | issue = 36 | pages = 12225–12236 | year = 1997 }}
=Natural occurrence=
Gaseous disulfur has been detected emanating from the surface of Jupiter's moon Io, from the vicinity of Pele volcano.{{cite journal|last1=Spencer|first1=J. R.|title=Discovery of Gaseous S2 in Io's Pele Plume|journal=Science|volume=288|issue=5469|year=2000|pages=1208–1210|issn=0036-8075|doi=10.1126/science.288.5469.1208|pmid=10817990|bibcode=2000Sci...288.1208S}}
Properties
The ground state of S2 is a triplet: a diradical, with two unpaired electrons like O2 and SO.{{cite book|first1=N. N.|last1=Greenwood|first2=A.|last2=Earnshaw|title=Chemistry of the Elements|publisher=Pergamon|location=New York|year=1986|postscript=;}} as cited in {{cite journal|doi=10.1080/10426509708545509|journal=Phosphorus, Sulfur, and Silicon|year=1997|volume=120|page=41|publisher=Gordon & Breach|location=Amsterdam, NL|title=The sulfur diatomics|first=David N.|last=Harpp}} It has the S–S bond length of 189 pm, much shorter than the S–S single bonds in S8, which are 206 pm long. Its Raman spectrum consists of a band at 715 cm−1.{{Cite book| last1 = Eckert | first1 = Bodo| last2 = Steudel | first2 = Ralf| chapter = Molecular Spectra of Sulfur Molecules and Solid Sulfur Allotropes | doi = 10.1007/b13181 | title = Elemental Sulfur and Sulfur-Rich Compounds II | series = Topics in Current Chemistry | volume = 231 | pages = 181–191| year = 2003 | isbn = 978-3-540-40378-4 }} The corresponding O–O band for O2 is found at 1556 cm−1.{{Cite journal|last1=Hill|first1=R.A.|last2=Esherick|first2=P.|last3=Owyoung|first3=A.|date=1983|title=High-resolution stimulated Raman spectroscopy of O2|journal=Journal of Molecular Spectroscopy|language=en|volume=100|issue=1|pages=119–133|doi=10.1016/0022-2852(83)90029-2|bibcode=1983JMoSp.100..119H}} The S-S bond energy is 430 kJ/mol compared to 498 kJ/mol for O2.({{RubberBible87th}}
Singlet disulfur is believed to be the product of trisulfides with triphenylphosphine dibromide, or the thermal decomposition of dialkoxy disulfides. However, the disulfur produced in that reaction is believed singlet because it undergoes formal hetero-Diels–Alder cycloadditions, not because of any spectroscopic evidence.{{cite book|doi=10.1002/9780470682531.pat0829|title=Peroxides|chapter=Sulfoxylic and thiosulfurous acids and their dialkoxy derivatives|first1=Sergei V.|last1=Makarov|first2=Anna S.|last2=Makarova|first3=Radu|last3=Silaghi-Dumitrescu|series=Chemistry of Functional Groups|year=2014|publisher=Wiley|page=297|isbn=978-0-470-68253-1 }}
Triplet disulfur readily photodissociates,{{cite journal|last1=Frederix|first1=Pim W. J. M.|last2=Yang|first2=Chung-Hsin|last3=Groenenboom|first3=Gerrit C.|last4=Parker|first4=David H.|last5=Alnama|first5=Koutayba|last6=Western|first6=Colin M.|last7=Orr-Ewing|first7=Andrew J.|title=Photodissociation Imaging of Diatomic Sulfur (S2)†|journal=The Journal of Physical Chemistry A|volume=113|issue=52|year=2009|pages=14995–15005|issn=1089-5639|doi=10.1021/jp905104u|pmid=19754091|bibcode=2009JPCA..11314995F|citeseerx=10.1.1.511.5087}} with a mean lifespan of 7.5 min in sunlight.{{cite journal|last1=Ahearn|first1=M. F.|last2=Schleicher|first2=D. G.|last3=Feldman|first3=P. D.|title=The discovery of S2 in comet IRAS-Araki-Alcock 1983d|journal=The Astrophysical Journal|volume=274|year=1983|pages=L99|issn=0004-637X|doi=10.1086/184158|bibcode=1983ApJ...274L..99A}}