Disulfur dioxide
structure of disulfur dioxide, S2O2
space-filling model of the disulfur dioxide molecule
Other names
SO dimer
3D model (JSmol)
  • InChI=1/O2S2/c1-3-4-2
  • O=[S][S]=O
Molar mass 96.1299 g/mol
Appearance gas
Occupational safety and health (OHS/OSH):
Main hazards
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Disulfur dioxide, dimeric sulfur monoxide or SO dimer is an oxide of sulfur with the formula S2O2.[2] The solid is unstable with a lifetime of a few seconds at room temperature.[3]


Disulfur dioxide adopts a 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 O−S−S angle is 112.7°. S2O2 has a dipole moment of 3.17 D.[4] It is 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 carbonyl sulfide 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 ⇌ 2 SO

Disulfur dioxide is also produced upon a microwave discharge in sulfur dioxide diluted in helium.[8] At a pressure of 0.1 mmHg (13 Pa), five percent of the result is S2O2.[9]

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


The ionization 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]

Reactions and decomposition

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

Decomposition of S2O2 proceeds via the following disproportionation reaction:

S2O2 → SO2 + 1/8 S8


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)2Pt(S2O2).[15] Iridium atoms can also form a complex: cis-[(dppe)2IrS2]Cl with sodium periodate oxidizes 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 triphenylphosphine to form triphenylphosphine oxide and triphenylphosphine sulfide.[16]


The S
radical 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. ^ a b Demaison, Jean; Vogt, Jürgen (2011). "836. O2S2 Disulfur dioxide" (PDF). Asymmetric Top Molecules, Part 3. Landolt–Börnstein: Group II Molecules and Radicals. Vol. 29D3. Springer. p. 492. doi:10.1007/978-3-642-14145-4_258. ISBN 9783642141454.
  2. ^ Holleman, Arnold F.; Wiber, Egon; Wiberg, Nils, eds. (2001). "Oxides of sulfur". Inorganic Chemistry. Academic Press. p. 530. ISBN 9780123526519.
  3. ^ Mitchell, Stephen C. (2004). Biological Interactions Of Sulfur Compounds. CRC Press. p. 7. ISBN 9780203362525.
  4. ^ a b Lovas, F. J. (1974). "Spectroscopic studies of the SO2 discharge system. II. Microwave spectrum of the SO dimer". The Journal of Chemical Physics. 60 (12): 5005. Bibcode:1974JChPh..60.5005L. doi:10.1063/1.1681015.
  5. ^ a b c Thorwirth, Sven; Theulé, P.; Gottlieb, C. A.; Müller, H. S. P.; McCarthy, M. C.; Thaddeus, P. (2006). "Rotational spectroscopy of S2O: vibrational satellites, 33S 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. ^ a b Cheng, Bing-Ming; Hung, Wen-Ching (1999). "Photoionization efficiency spectrum and ionization energy of S2O2". The Journal of Chemical Physics. 110 (1): 188. Bibcode:1999JChPh.110..188C. doi:10.1063/1.478094. ISSN 0021-9606.
  7. ^ Murakami, Yoshinori; Onishi, Shouichi; Kobayashi, Takaomi; Fujii, Nobuyuki; Isshiki, Nobuyasu; Tsuchiya, Kentaro; Tezaki, Atsumu; Matsui, Hiroyuki (2003). "High Temperature Reaction of S + SO2 → SO + SO: Implication of S2O2 Intermediate Complex Formation". The Journal of Physical Chemistry A. 107 (50): 10996–11000. Bibcode:2003JPCA..10710996M. doi:10.1021/jp030471i. ISSN 1089-5639.
  8. ^ a b Field, T. A.; Slattery, A. E.; Adams, D. J.; Morrison, D. D. (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. S2CID 122789729. Archived from the original (PDF) on 2015-09-24. Retrieved 2013-05-13.
  9. ^ Sahoo, Balaram; Nayak, Nimai Charan; Samantaray, Asutosh; Pujapanda, Prafulla Kumar (2012). Inorganic Chemistry. PHI Learning. p. 461. ISBN 9788120343085. Retrieved 2013-05-16.
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  11. ^ a b Frandsen, B. N.; Wennberg, P. O.; Kjærgaard, H. G. (2016). "Identification of OSSO as a near-UV absorber in the Venusian atmosphere" (PDF). Geophysical Research Letters. 43 (21): 11146–11155. Bibcode:2016GeoRL..4311146F. doi:10.1002/2016GL070916.
  12. ^ "Rare molecule on Venus may help explain planet's weather". CBC News. Retrieved 2016-11-11.
  13. ^ Herron, J. T.; Huie, R. E. (1980). "Rate constants at 298 K for the reactions SO + SO + M → (SO)2 + M and SO + (SO)2 → SO2 + S2O". Chemical Physics Letters. 76 (2): 322–324. Bibcode:1980CPL....76..322H. doi:10.1016/0009-2614(80)87032-1.
  14. ^ Halcrow, Malcolm A.; Huffman, John C.; Christou, George (1994). "Synthesis, Characterization, and Molecular Structure of the New S2O Complex Mo(S2O)(S2CNEt2)3·1/2Et2O" (PDF). Inorganic Chemistry. 33 (17): 3639–3644. doi:10.1021/ic00095a005. ISSN 0020-1669.
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