Sulfur monoxide

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Sulfur monoxide
Skeletal formula of sulfur monoxide Sulfur monoxide.svg
Skeletal formula of sulfur monoxide
Spacefill model of sulfur monoxide Sulfur-monoxide-3D-vdW.png
Spacefill model of sulfur monoxide
IUPAC name
Sulfur monoxide[ citation needed ]
Systematic IUPAC name
Oxidosulfur [1]
3D model (JSmol)
MeSH sulfur+monoxide
PubChem CID
  • InChI=1S/OS/c1-2 Yes check.svgY
  • InChI=1/OS/c1-2
  • O=S
Molar mass 48.064 g mol−1
AppearanceColourless gas
log P 0.155
Std molar
221.94 J K−1 mol−1
5.01 kJ mol−1
Related compounds
Related compounds
Triplet oxygen
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Sulfur monoxide is an inorganic compound with formula S O . It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2 (disulfur dioxide). 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, that is, each molecule has two unpaired electrons. [2] 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). [2]

The molecule is excited with near infrared radiation to the singlet state (with no unpaired electrons). The singlet state is believed to be more reactive than the ground triplet state, in the same way that singlet oxygen is more reactive than triplet oxygen. [3]

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: [4] as well as more complex examples, such as a trisulfide oxide, C10H6S3O. [5]

C2H4SO → C2H4 + SO

The SO molecule is thermodynamically unstable, converting initially to S2O2. [2] SO inserts into alkenes, alkynes and dienes producing thiiranes, molecules with three-membered rings containing sulfur. [6]

Generation under extreme conditions

In the laboratory, sulfur monoxide can be produced by treating sulfur dioxide with sulfur vapor in a glow discharge. [2] It has been detected in single-bubble sonoluminescence of concentrated sulfuric acid containing some dissolved noble gas. [7]

Benner and Stedman developed a chemiluminescence detector for sulfur via the reaction between sulfur monoxide and ozone: [8]

SO + O3 → SO2* + O2
SO2* → SO2 + hν

(* indicates an excited state)


Ligand for transition metals

As a ligand SO can bond in a number different ways: [9] [10]


Sulfur monoxide has been detected around Io, one of Jupiter's moons, both in the atmosphere [13] and in the plasma torus. [14] It has also been found in the atmosphere of Venus, [15] in Comet Hale–Bopp, [16] in 67P/Churyumov–Gerasimenko, [17] and in the interstellar medium. [18]

On Io, SO is thought to be produced both by volcanic and photochemical routes. The principal photochemical reactions are proposed as follows: [19]

O + S2 → S + SO
SO2 → SO + O

Sulfur monoxide has been found in NML Cygni. [20]

Biological chemistry

Sulfur monoxide may have some biological activity. The formation of transient SO in the coronary artery of pigs has been inferred from the reaction products, carbonyl sulfide and sulfur dioxide. [21]

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 (similar flammability to methane) and when burned produces sulfur dioxide, a poisonous gas.

Sulfur monoxide dication

Sulfur dioxide SO2 in presence of hexamethylbenzene C6(CH3)6 can be protonated under superacidic conditions (HF·AsF5) to give the non-rigid π-complex C6(CH3)6SO2+. The SO2+ moiety can essentially move barrierless over the benzene ring. The S−O bond length is 142.4(2) pm. [22]

C6(CH3)6 + SO2 + 3 HF·AsF5 → [C6(CH3)6SO][AsF6]2 + [H3O][AsF6]

Disulfur dioxide

The structure of disulfur dioxide, S2O2 Disulfur-dioxide-2D-dimensions.png
The structure of disulfur dioxide, S2O2
A space-filling model of the disulfur dioxide molecule Disulfur-dioxide-3D-vdW-A.png
A space-filling model of the disulfur dioxide molecule

SO converts to disulfur dioxide (S2O2). [23] Disulfur dioxide is a 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 O−S−S angle is 112.7°. S2O2 has a dipole moment of 3.17  D. [23]

Related Research Articles

<span class="mw-page-title-main">Carbon monoxide</span> Colourless, odourless, tasteless and toxic gas

Carbon monoxide is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simplest carbon oxide. In coordination complexes the carbon monoxide ligand is called carbonyl. It is a key ingredient in many processes in industrial chemistry.

In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. While fully ionic bonds are not found in nature, many bonds exhibit strong ionicity, making oxidation state a useful predictor of charge.

In chemistry, a diradical is a molecular species with two electrons occupying molecular orbitals (MOs) which are degenerate. The term "diradical" is mainly used to describe organic compounds, where most diradicals are extremely reactive and in fact rarely isolated. Diradicals are even-electron molecules but have one fewer bond than the number permitted by the octet rule.

<span class="mw-page-title-main">Disulfur decafluoride</span> Chemical compound

Disulfur decafluoride is a chemical compound with the formula S2F10. It was discovered in 1934 by Denbigh and Whytlaw-Gray. Each sulfur atom of the S2F10 molecule is octahedral, and surrounded by five fluorine atoms and one sulfur atom. The two sulfur atoms are connected by a single bond. In the S2F10 molecule, the oxidation state of each sulfur atoms is +5, but their valency is 6. S2F10 is highly toxic, with toxicity four times that of phosgene.

<span class="mw-page-title-main">Lower sulfur oxides</span>

The lower sulfur oxides are a group of inorganic compounds with the formula SmOn, where 2m > n. These species are often unstable and thus rarely encountered in everyday life. They are significant intermediates in the combustion of elemental sulfur. Some well characterized examples include sulfur monoxide (SO), its dimer S2O2, and a series of cyclic sulfur oxides, SnOx (x = 1, 2), based on cyclic Sn rings.

In enzymology, carbon monoxide dehydrogenase (CODH) (EC is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Disulfur dinitride</span> Chemical compound

Disulfur dinitride is the chemical compound with the formula S2N2.

<span class="mw-page-title-main">Disulfur</span> Chemical compound

Disulfur is the diatomic molecule with the formula S2. 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. The instability of S2 is usually described in the context of the double bond rule.

<span class="mw-page-title-main">Disulfur monoxide</span> Chemical compound

Disulfur monoxide or sulfur suboxide is an inorganic compound with formula S2O, one of the lower sulfur oxides. It is a colourless gas and condenses to give a roughly dark red coloured solid that is unstable at room temperature.

In organometallic chemistry, metal sulfur dioxide complexes are complexes that contain sulfur dioxide, SO2, bonded to a transition metal. Such compounds are common but are mainly of theoretical interest. Historically, the study of these compounds has provided insights into the mechanisms of migratory insertion reactions.

<span class="mw-page-title-main">Trisulfur</span> Chemical compound

The S
, known as trisulfur, sulfur trimer, thiozone, or triatomic sulfur, is a cherry-red allotrope of sulfur. It comprises about 10% of vaporised sulfur at 713 K (440 °C; 824 °F) and 1,333 Pa (10.00 mmHg; 0.1933 psi). It has been observed at cryogenic temperatures as a solid. Under ordinary conditions it converts to cyclooctasulfur.

<span class="mw-page-title-main">Disulfur dioxide</span> Chemical compound

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

The chalcogens react with each other to form interchalcogen compounds.

<span class="mw-page-title-main">Thiosulfurous acid</span> Chemical compound

Thiosulfurous acid (HS−S(=O)−OH) is a hypothetical compound with the formula S2(OH)2. Attempted synthesis leads to polymers. It is a low oxidation state (+1) sulfur acid. It is the equivalent acid for disulfur monoxide. Salts derived from thiosulfurous acid, which are also unknown, are named "thiosulfites" or "sulfurothioites". The ion is S=SO2−

Difluoroamino sulfur pentafluoride is a gaseous chemical compound of fluorine, sulfur, and nitrogen. It is unusual in having a hexa-coordinated sulfur atom with a link to nitrogen. Other names for this substance include difluoro(pentafluorosulfur)amine, pentafluorosulfanyldifluoramine, and pentafluorosulfanyl N,N-difluoramine.

<span class="mw-page-title-main">Difluorodisulfanedifluoride</span> Chemical compound

1,1,1,2-tetrafluorodisulfane, also known as 1,2-difluorodisulfane 1,1-difluoride or just difluorodisulfanedifluoride (FSSF3) is an unstable molecular compound of fluorine and sulfur. The molecule has a pair of sulfur atoms, with one fluorine atom on one sulfur, and three fluorine atoms on the other. It has the uncommon property that all the bond lengths are different. The bond strength is not correlated with bond length but is inversely correlated with the force constant (Badger's rule). The molecule can be considered as sulfur tetrafluoride in which a sulfur atom is inserted into a S-F bond.

A heterocumulene is a molecule or ion containing a chain of at least three double bonds between consecutive atoms, in which one or more atoms in the doubly bonded chain is a heteroatom. Such species are analogous to a cumulene in which the chain of doubly bonded atoms contains only carbon, except that at least one carbon is replaced by a heteroatom. Some authors relax the definition to include species with chains of only two double bonds between consecutive atoms, also known as heteroallenes.

<span class="mw-page-title-main">Sulfoxylic acid</span> Chemical compound

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

Dihydroxydisulfane or hypodithionous acid is a reduced sulfur oxyacid with sulfur in a formal oxidation state of +1. The structural formula is HOSSOH, with all atoms arranged in a chain. It is an isomer of thiosulfurous acid but is lower in energy. Other isomers include HOS(=O)SH, HOS(=S)OH, and HS(=O)2SH. Disulfur monoxide, S2O, can be considered as the anhydride. Unlike many of these other reduced sulfur acids, dihydroxydisulfane can be formed in a pure state by reacting hydrogen sulfide with sulfur dioxide at −70 °C in dichlorodifluoromethane.

A sulfite sulfate is a chemical compound that contains both sulfite and sulfate anions [SO3]2− [SO4]2−. These compounds were discovered in the 1980s as calcium and rare earth element salts. Minerals in this class were later discovered. Minerals may have sulfite as an essential component, or have it substituted for another anion as in alloriite. The related ions [O3SOSO2]2− and [(O2SO)2SO2]2− may be produced in a reaction between sulfur dioxide and sulfate and exist in the solid form as tetramethyl ammonium salts. They have a significant partial pressure of sulfur dioxide.


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