Disulfur dioxide

Disulfur dioxide, dimeric sulfur monoxide or SO dimer is an oxide of sulfur.[2] The solid is unstable with a lifetime of a few seconds at room temperature.[3]

Disulfur dioxide
Other names
SO dimer
3D model (JSmol)
Molar mass 96.1299 g/mol
Appearance gas
Main hazards toxic
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references


Disulfur dioxide adopts cis-planar structure with C2v symmetry. The S-O bond length is 145.8 pm, shorter than in sulfur monoxide. The S-S bond length is 202.45 pm and the OSS angle is 112.7°. S2O2 has a dipole moment of 3.17 D.[4] an asymmetric top molecule.[1][5]


Sulfur monoxide (SO) converts to disulfur dioxide (S2O2) spontaneously and reversibly.[4] So the substance can be generated by methods that produce sulfur monoxide. Disulfur dioxide has also been formed by an electric discharge in sulfur dioxide.[5] Another laboratory procedure is to react oxygen atoms with carbon oxysulfide or carbon disulfide vapour.[6]

Although most forms of elemental sulfur (S8 and other rings and chains) do not combine with SO2, atomic sulfur does so to form sulfur monoxide, which dimerizes:[7]

S + SO2 S2O2
S2O2 ⇌ 2SO

Disulfur dioxide is also produced upon a microwave discharge in sulfur dioxide diluted in helium.[8] At a pressure of 0.1 mm Hg,five percent of the result is S2O2.[9]

Disulfur dioxide is formed transiently when hydrogen sulfide and oxygen undergo flash photolysis.[10]


The ionisation energy of disulfur dioxide is 9.93±0.02  eV.[6]

Disulfur dioxide absorbs at 320–400 nm, as observed of the Venusian atmosphere,[11] and is believed to have contributed to the greenhouse effect on that planet.[12]


Although disulfur dioxide exists in equilibrium with sulfur monoxide, it also reacts with sulfur monoxide to form sulfur dioxide and disulfur monoxide.[8][13]


S2O2 can be a ligand with transition metals. It binds in the η2-S,S' position with both sulfur atoms linked to the metal atom.[14] This was first shown in 2003. The bis-(trimethylphosphine) thiirane S-oxide complex of platinum, when heated in toluene at 110 °C loses ethylene, and forms a complex with S2O2: (Ph3P)2PtS2O2.[15] Iridium atoms can also form a complex: cis-[(dppe)2IrS2]Cl with sodium periodate oxidises to [(dppe)2IrS2O] and then to [(dppe)2IrS2O2], with dppe being 1,2-Bis(diphenylphosphino)ethane.[16][17] This substance has the S2O2 in a cis position. The same conditions can make a trans complex, but this contains two separate SO radicals instead. The iridium complex can be decomposed with triphenyl phosphine to form triphenyl phosphine oxide, and triphenyl phosphine sulfide.[16]


The S2O2 anion has been observed in the gas phase. It may adopt a trigonal shape akin to SO3.[18]



Transition Frequency MHz[5]
21,1−20,2 11013.840
41,3−40,4 14081.640
11,1−00,0 15717.946
40,4−31,3 16714.167
31,3−20,2 26342.817
42,2−41,3 26553.915
22,0−21,1 28493.046
60,6−51,5 30629.283
52,4−51,5 35295.199
51,5−40,4 35794.527

In the Solar System

There is a some evidence that disulfur dioxide may be a small component in the atmosphere of Venus, and that it may substantially contribute of the planet's severe greenhouse effect.[11] It is not found in any substantive quantity in Earth's atmosphere.


  1. Demaison, Jean; Vogt, Jürgen (2011). "836 O2S2 Disulfur dioxide" (PDF). Asymmetric Top Molecules, Part 3. Landolt-Börnstein - Group II Molecules and Radicals. 29D3. Springer. p. 492. doi:10.1007/978-3-642-14145-4_258. ISBN 978-3-642-14145-4.
  2. Arnold F. Holleman; Egon Wiber; Nils Wiberg, eds. (2001). "Oxides of sulfur". Inorganic Chemistry. Academic Press. p. 530. ISBN 9780123526519.
  3. Mitchell, Stephen C. (3 September 2004). Biological Interactions Of Sulfur Compounds. CRC Press. p. 7. ISBN 978-0203362525.
  4. Spectroscopic studies of the SO2 discharge system. II. Microwave spectrum of the SO dimer Lovas F. J., Tiemann E., Johnson D.R. The Journal of Chemical Physics (1974), 60, 12, 5005-5010 doi:10.1063/1.1681015
  5. Thorwirth, Sven; P. Theulé; C. A. Gottlieb; H. S. P. Müller; M. C. McCarthy; P. Thaddeus (23 February 2006). "Rotational spectroscopy of S2O: vibrational satellites, 33 S isotopomers, and the submillimeter-wave spectrum" (PDF). Journal of Molecular Structure. 795 (1–3): 219–229. Bibcode:2006JMoSt.795..219T. doi:10.1016/j.molstruc.2006.02.055.
  6. Cheng, Bing-Ming; Wen-Ching Hung (1999). "Photoionization efficiency spectrum and ionization energy of S[sub 2]O[sub 2]". The Journal of Chemical Physics. 110 (1): 188. Bibcode:1999JChPh.110..188C. doi:10.1063/1.478094. ISSN 0021-9606.
  7. Murakami, Yoshinori; Shouichi Onishi; Takaomi Kobayashi; Nobuyuki Fujii; Nobuyasu Isshiki; Kentaro Tsuchiya; Atsumu Tezaki; Hiroyuki Matsui (2003). "High Temperature Reaction of S + SO2→ SO + SO: Implication of S2O2Intermediate Complex Formation". The Journal of Physical Chemistry A. 107 (50): 10996–11000. Bibcode:2003JPCA..10710996M. doi:10.1021/jp030471i. ISSN 1089-5639.
  8. Field, T A; A E Slattery; D J Adams; D D Morrison (2005). "Experimental observation of dissociative electron attachment to S2O and S2O2 with a new spectrometer for unstable molecules" (PDF). Journal of Physics B: Atomic, Molecular and Optical Physics. 38 (3): 255–264. Bibcode:2005JPhB...38..255F. doi:10.1088/0953-4075/38/3/009. ISSN 0953-4075. Archived from the original (PDF) on 2015-09-24. Retrieved 2013-05-13.
  9. Pujapanda, Balaram Sahoo, Nimain C. Nayak, Asutosh Samantaray, Prafulla K.; Balaram, Sahoo; Charan, nayak Nimai; samantaray Asutosh; pujapanda Prafulla Kumar (2012). Inorganic Chemistry. PHI Learning Pvt. Ltd. p. 461. ISBN 9788120343085. Retrieved 16 May 2013.
  10. Compton, R. G.; Bamford, C.H.; Tipper, C.F.H. (1972). "Oxidation of H2S". Reactions of Non-Metallic Inorganic Compounds. Comprehensive Chemical Kinetics. Elsevier. p. 50. ISBN 978-0080868011.
  11. BN Frandsen; PO Wennberg; HG Kjaergaard (2016). "Identification of OSSO as a near-UV absorber in the Venusian atmosphere" (PDF). Geophys. Res. Lett. 43 (21): 11, 146. Bibcode:2016GeoRL..4311146F. doi:10.1002/2016GL070916.
  12. "Rare molecule on Venus may help explain planet's weather - Technology & Science - CBC News". Cbc.ca. Retrieved November 11, 2016.
  13. Herron, J. T.; R. E. Huie (1980). "Rate constants at 298 K for the reactions sulfur monoxide + sulfur monoxide + M -> dimeric sulfur monoxi de + M and sulfur monoxide + dimeric sulfur monoxide -> sulfur dioxide + sulfur oxide (S2O)". Chemical Physics Letters. 76 (2): 322–324. Bibcode:1980CPL....76..322H. doi:10.1016/0009-2614(80)87032-1.
  14. Halcrow, Malcolm A.; John C. Huffman; George Christou (1994). "Synthesis, Characterization, and Molecular Structure of the New S2O Complex Mo(S2O)(S2CNEt2)3.cntdot.1/2Et2O" (PDF). Inorganic Chemistry. 33 (17): 3639–3644. doi:10.1021/ic00095a005. ISSN 0020-1669.
  15. Lorenz, Ingo-Peter; Jürgen Kull (1986). "Complex Stabilization of Disulfur Dioxide in the Fragmentation of ThiiraneS-Oxide on Bis(triphenylphosphane)platinum(0)". Angewandte Chemie International Edition in English. 25 (3): 261–262. doi:10.1002/anie.198602611. ISSN 0570-0833.
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  17. Nagata, K; N. Takeda; N Tokitoh N (2003). "Unusual Oxidation of Dichalcogenido Complexes of Platinum". Chemical Letters. 32 (2): 170–171. doi:10.1246/cl.2003.170. ISSN 0366-7022.
  18. Clements, Todd G.; Hans-Jürgen Deyerl; Robert E. Continetti (2002). "Dissociative Photodetachment Dynamics of S2O2-" (PDF). The Journal of Physical Chemistry A. 106 (2): 279–284. Bibcode:2002JPCA..106..279C. doi:10.1021/jp013329v. ISSN 1089-5639. Retrieved 2013-05-13.
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