Sulfur monoxide

Sulfur monoxide is a chemical compound with formula sulfuroxygen and CAS number 13827-32-2. It is an unstable species only found in the gas phase where it is in equilibrium with a dimeric form, S₂O₂ (sometimes called disulfur dioxide) which can be represented as OSSO"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] . Sulfur monoxide has been detected around Io, one of Jupiter's moons, both in the atmosphere ["Io’s atmosphere: Not yet understood" Lellouch, E. 1996. Icarus 124, 1–21.] and in the plasma torus ["Detection of SO in Io's Exosphere" Russell C.T., Kivelson M.G. Science (2000): 287, 5460, 1998 – 1999, doi|10.1126/science.287.5460.1998] . It has also been found in the atmosphere of Venus ["International Ultraviolet Explorer observations of Venus SO₂ and SO " Na, Chan Y. ; Esposito, L.W. ; Skinner, T.E; Journal of Geophysical Research ; 95 1990, 7485-7491] , in the Hale-Bopp comet ["New Molecular Species in Comet C/ 1995 O1 (Hale-Bopp) Observed with the Caltech S submillimeter Observatory" D. C. Lis, D. M. Mehringer, D. Benford, M. Gardner, T. G. Phillips, D. Bockelée-Morvan, N. Biver, P. Colom, J. Crovisier, D.Despois and H.Rauer Earth, Moon, and Planets Volume 78, Numbers 1-3 / July, 1997 doi|10.1023/A:1006281802554] and in interstellar space ["Observations of interstellar sulfur monoxide" Gottlieb, C. A.; Gottlieb,E.W.; Litvak,M.M.; Ball,J.A.; Pennfield,H. Astrophysical Journal, 1, 219, (1978),77-94 doi|10.1086/155757] .

tructure and bonding

The SO molecule has a triplet ground state similar to dioxygen, O₂, with 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 S₂O₂ dimer is planar molecule with C_2v symmetry, with two SO units joined via the sulfur atoms, and the oxygen atoms in a "cis" configuration. 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 OSS angle is 112.7°. It has a dipole moment, μ = 3.17 D.

Production and reactions

In the laboratory sulfur monoxide be made reacting sulfur dioxide with sulfur vapour in a glow discharge and in single bubble sonoluminescence of concentrated sulfuric acid containing some dissolved noble gas ["The temperatures of single-bubble sonoluminescence (A)" Suslick K.S. and Flannigan D.J., The Journal of the Acoustical Society of America ( 2004) 116, 4, 2540] .
Production of the transient SO molecule as a reagent in organic syntheses has been investigated. Research has centred on using compounds that decompose under reaction conditions to "extrude" SO. Examples include the decomposition of the relatively simple molecule thiirane 1-oxide ["Sulfur Monoxide Chemistry. The Nature of SO from Thiirane Oxide and the Mechanism of Its Reaction with Dienes" Chao P., Lemal D. M. Journal of the American Chemical Society 95,3: (1973) 920 doi|10.1021/ja00784a049] ::C₂H₄OS → C₂H₄(g) + SO(g)as well as more complex examples e.g. a trisulfide oxide, C₁₀H₆S₃O, ["A novel recyclable sulfur monoxide transfer reagent." Grainger RS, Procopio A, Steed JW. Org Lett. 2001 3(22), 3565-8.]
On Io the production of SO is believed to be both volcanic and also photochemical. The principal photochemical reactions proposed ["Photochemistry of a Volcanically Driven Atmosphere on Io: Sulfur and Oxygen Species from a Pele-Type Eruption"Moses J.I., Zolotov M.Y., Fegley B.Icarus 156, 76–106 (2002) doi|10.1006/icar.2001.6758] are:

: O + S₂ → S + SO

: SO₂ + hν → SO +O

The SO molecule is thermodynamically unstable . The transient SO molecule can be trapped by the formation of transition metal complexes. As a ligand SO can bond in a number different ways ["Sulfur: Inorganic Chemistry" Woollins JD, Encyclopedia of Inorganic Chemistry (1995), John Wiley and Sons ISBN 0-471-93620-0] :
*σ donation forming a bent bond with the metal
*bridging across 2 or 3 metal centres via sulfur
*edge on bridging

SO inserts into alkenes, alkynes and dienes producing molecules with three membered rings containing sulfur. [" [1+2] Cycloadditions of Sulfur Monoxide (SO) to Alkenes and Alkynes and [1+4] Cycloadditions to Dienes (Polyenes). Generation and Reactions of Singlet SO?" Juzo Nakayama , Yumi Tajima , Piao Xue-Hua , Yoshiaki Sugihara J. Am. Chem. Soc.; 2007; 129(23) pp 7250 - 7251; (Communication)doi|10.1021/ja072044e]
The triplet ground state molecule with two unpaired electrons can be excited by near infrared light to the singlet state with no unpaired electrons. The singlet state is believed be more reactive than the ground state triplet state, in the same way that singlet oxygen is more reactive than the triplet ground state ["Near-Infrared-Light-Induced Reaction of Singlet SO with Allene and Dimethylacetylene in a Rare Gas Matrix. Infrared Spectra of Two Novel Episulfoxides" Salama F; Frei H J. Phys. Chem. 1989, 93, 1285-1292] .
Sulfur monoxide may have some biological activity, the formation of transient SO in porcine coronary artery has been inferred from the reaction products ["Identification of carbonyl sulfide and sulfur dioxide in porcine coronary artery by gas chromatography/mass spectrometry, possible relevance to EDHF" Balazy M, Abu-Yousef IA, Harpp DN, Park J.Biochem Biophys Res Commun. 2003 Nov 21;311(3):728-34 ] .

Uses

A chemiluminescence detector for sulfur has been reported ["Chemical Mechanism and Efficiency of the Sulfur Chemiluminescence Detector" Benner, R. L., Stedman, D. H. Applied Spectroscopy, 48, 7, (1994), 848-851doi|10.1366/0003702944029901 ] that is based on the reactions::SO + O₃ → SO₂(excited) + O₂:SO₂(excited) → SO₂ + hν

References