Disulfur monoxide or sulfur suboxide is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with formula S₂O, one of the

lower sulfur oxides 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 su ...

. It is a colourless gas and condenses to give a roughly dark red coloured solid that is unstable at room temperature. occurs rarely in natural atmospheres, but can be made by a variety of laboratory procedures. For this reason, its spectroscopic signature is very well understood.

Structure and spectrum

Condensed solid S₂O absorbs at (roughly

indigo Indigo is a deep color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the ancient dye of the same name. The word "indigo" comes from the Latin word ''indicum'', m ...

) and (roughly

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

). These bands have been assigned to decomposition products S₃ and S₄. In the ultraviolet, S₂O has absorption band systems in the ranges 250–340 nm and 190–240 nm. There are bands at 323.5 and 327.8 nm. The band in the 315–340 nm range is due to the transition. Gaseous disulfur monoxide does not absorb in the

visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye wil ...

. The microwave spectrum of S₂O has the following rotational parameters: ''A'' = 41915.44 MHz, ''B'' = 5059.07 MHz, and ''C'' = 4507.19 MHz. Moreover, the microwave spectrum suggests the S−S−O angle is 117.88° with S−S and S−O bond lengths of 188.4 and 146.5 pm, respectively. In the 327.8 nm excited state, the central angle tightens to 109°. The harmonic frequency for S−S stretching is 415.2 cm⁻¹.

Synthesis

Historical

Disulfur monoxide was discovered by Peter W. Schenk in 1933 with a

glow discharge A glow discharge is a plasma formed by the passage of electric current through a gas. It is often created by applying a voltage between two electrodes in a glass tube containing a low-pressure gas. When the voltage exceeds a value called the str ...

though sulfur vapour and

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

. He discovered that the gas could survive for hours at single digit pressures of mercury in clean glass, but it decomposed near . Schenk assigned the formula as SO and called it

sulfur monoxide 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 ( disulfur dioxide). It has been detected in space but is rarely encountered intact otherwise. St ...

. In 1956, D. J. Meschi and R. J. Myers established the formula as S₂O.

Preparation

Oxidizing

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

with

copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite. It is ...

: :3 S₈ + 12 CuO → 12 CuS + 4 S₂O + 4 SO₂ A relatively pure generator is the reaction of

thionyl chloride Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...

with silver(I) sulfide: :SOCl₂ + Ag₂S → 2 AgCl + S₂O Also 5,6-di-''tert''-butyl-2,3,7-trithiabicyclo .2.1ept-5-ene 2-''endo''-7-''endo''-dioxide decomposes upon heating with release of S₂O:

Occurrence

Volcanism

Volcanoes on Io produce substantial quantities of . It can form between 1% and 6% when hot 100-bar S₂ and SO₂ gas erupts from volcanoes. It is believed that Pele on Io is surrounded by solid S₂O.

Terran atmosphere

Disulfur monoxide is too unstable to survive at standard conditions, but transient sources include

incomplete combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

of sulfur vapor and thermal decomposition of

in a

As a ligand

Disulfur monoxide occurs as a

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

bound to

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

s, typically with

hapticity In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a l ...

2. Examples include ; ; and . These complexes are closely related to

transition metal sulfur dioxide complex In organometallic chemistry, metal sulfur dioxide complexes are complexes that contain sulfur dioxide, , bonded to a transition metal. Such compounds are common but are mainly of theoretical interest. Historically, the study of these compoun ...

es.

Reactions

On decomposition at room temperature it forms SO₂ via the formation of polysulfur oxides: :2 S₂O → "S₃" + SO₂ reacts with diazoalkanes to form

dithiirane 1-oxides In organic chemistry, episulfides are a class of organic compounds that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiir ...

References

{{commons category, Disulfur monoxide Gases Sulfur oxides Interchalcogens Triatomic molecules