A thiosulfoxide or thiothionyl compound is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

containing a

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

, with the formula , where R and R' represent any group (typically

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

alkoxy In chemistry, the alkoxy group is an alkyl group which is Single bond, singularly bonded to oxygen; thus . Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the ...

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

or other

organyl In organic and organometallic chemistry, an organyl group (commonly denoted by the letter " R") is an organic substituent with one (sometimes more) free valence electron(s) at a carbon atom.. The term is often used in chemical patent literatur ...

residues. The thiosulfoxide has a molecular shape known as trigonal pyramidal. Its coordination is also trigonal pyramidal. The point group of the thiosulfoxide is C_s. A 1982 review concluded that there was as yet no definitive evidence for the existence of stable thiosulfoxides which can be attributed to the

double bond rule In chemistry, the double bond rule states that elements with a principal quantum number (''n'') greater than 2 for their valence electrons ( period 3 elements and higher) tend not to form multiple bonds (e.g. double bonds and triple bonds). Do ...

which states that elements of period 3 and beyond do not form multiple bonds. The related

sulfoxide In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...

s of the type are very common. Many compounds containing a sulfur-sulfur double bond have been reported in the past although only a few verified classes of actually stable compounds exist, closely related to thiosulfoxides. Thiothionylfluoride-2D-dimensions

Sulfur-sulfur double bonds can be stabilized with

electron-withdrawing group An electron-withdrawing group (EWG) is a Functional group, group or atom that has the ability to draw electron density toward itself and away from other adjacent atoms. This electron density transfer is often achieved by resonance or inductive effe ...

s in so-called thionosulfites of the type . These compounds can be prepared by reaction of

diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...

s with

disulfur dichloride Disulfur dichloride (or disulphur dichloride by the British English spelling) is the inorganic compound of sulfur and chlorine with the Chemical formula, formula . It is an amber oily liquid. Sometimes, this compound is incorrectly named ''sulfur ...

. Sulfur halides such as disulfur dichloride, , can convert to the branched

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

thiothionyl chloride, ; disulfur difluoride exists as an equilibrium mixture with thiothionyl fluoride, , which is thermodynamically more stable. These disulfide isomerizations are occasionally studied ''

in silico In biology and other experimental sciences, an ''in silico'' experiment is one performed on a computer or via computer simulation software. The phrase is pseudo-Latin for 'in silicon' (correct ), referring to silicon in computer chips. It was c ...

''. ''N''-(Thiosulfinyl)amines of the type are another group of stable compounds containing a S=S bond. The first such compound was prepared in 1974 reaction of the

nitroso In organic chemistry, nitroso refers to a functional group in which the nitric oxide () group is attached to an organic moiety. As such, various nitroso groups can be categorized as ''C''-nitroso compounds (e.g., nitrosoalkanes; ), ''S''-nitros ...

compound ''N'',''N''-dimethyl-''p''-nitrosoaniline with tetraphosphorus decasulfide. Heating to 200 °C extrudes sulfur in this compound and forms the corresponding

azo compound Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups). IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...

Disulfur monoxide Disulfur monoxide or sulfur suboxide is an inorganic compound with the 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. occurs rar ...

S=S=O is stable at 20 °C for several days. Occasionally

thiosulfate Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...

s are depicted as having a S=S unit but the sulfur-sulfur bond in it is in fact a single bond.

References

{{Reflist Sulfur compounds