Sulfur monoxide is an inorganic compound with formula. It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2. 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, i.e. each molecule has two unpaired electrons. The S−O bond length of 148.1 pm is similar to that found in lower sulfur oxides but is longer than the S−O bond in gaseous S2O, SO2 and SO3. The molecule is excited with near infrared radiation to the singlet state. The singlet state is believed to be more reactive than the ground state triplet state, in the same way that singlet oxygen is more reactive than the triplet oxygen.
Production and reactions
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: as well as more complex examples, such as a trisulfide oxide, C10H6S3O, The SO molecule is thermodynamically unstable, converting initially to S2O2. SO inserts into alkenes, alkynes and dienes producing molecules with three membered rings containing sulfur.
As a ligand SO can bond in a number different ways:
a terminal ligand, with a bent M-O-S arrangement, for example with titanium oxyfluoride.
a terminal ligand, with a bent M-S-O arrangement, analogous to bent nitrosyl
bridging across 2 or 3 metal centres, as in Fe3S9
Sideways on with vanadium, niobium, and tantalum.
Astrochemistry
Sulfur monoxide has been detected around Io, one of Jupiter's moons, both in the atmosphere and in the plasma torus. It has also been found in the atmosphere of Venus, in the Hale-Bopp comet and in the interstellar medium. On Io, SO is thought to be produced both by volcanic and photochemical routes. The principal photochemical reactions are proposed as follows: Sulfur monoxide has been found in the largest star known, NML Cygni.
Biological chemistry
Sulfur monoxide may have some biological activity, the formation of transient SO in porcine coronary artery has been inferred from the reaction products.
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 and when burned produces sulfur dioxide, a poisonous gas.
Sulfur monoxide dication
Sulfur dioxide SO2 in presence of hexamethylbenzene C66 can be protonated under superacidic conditions to give the non-rigid π-complex C66SO2+. The SO2+ moiety can essientially move barrierless over the benzene ring. The S-O bond length is 1.424 Å. C66 + SO2 + 3 HF + 3 AsF5 -> 2 +
SO converts to disulfur dioxide. Disulfur dioxide is 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 OSS angle is 112.7°. S2O2 has a dipole moment of 3.17 D.
