
In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, thioketones (; also known as thiones or thiocarbonyls) are
organosulfur compound
Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...
s related to conventional
ketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
s in which the oxygen has been replaced by a sulfur. Instead of a structure of , thioketones have the structure , which is reflected by the prefix "
thio-" in the name of the functional group. Thus the simplest thioketone is
thioacetone, the sulfur analog of
acetone
Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
. Unhindered alkylthioketones typically tend to form
polymers
A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...
or
rings.
Structure and bonding
The C=S bond length of thiobenzophenone is 1.63 Å, which is comparable to 1.64 Å, the C=S bond length of thioformaldehyde, measured in the gas phase. Due to steric interactions, the phenyl groups are not coplanar and the dihedral angle SC-CC is 36°.
Unhindered dialkylthiones polymerize or oligomerize but thio
camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...
is well characterized red solid.

Consistent with 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 ...
, most alkyl thioketones are unstable with respect to dimerization.
[Organosulfur Chemistry I: Topics in Current Chemistry, 1999, Volume 204/1999, 127-181, ] The energy difference between the p orbitals of sulfur and carbon is greater than that between oxygen and carbon in ketones.
[Fisera, L.; Huisgen, R.; Kalwinsch, I.; Langhals, E.; Li, X.; Mloston, G.; Polborn, K.; Rapp, J.; Sicking, W.; Sustmann, R. "New Thione Chemistry". Pure Appl. Chem., 1996, 68, 789-798. ] The relative difference in energy and diffusity of the atomic orbitals of sulfur compared with carbon results in poor overlap of the atomic orbitals and the energy gap between the
HOMO and LUMO is thus reduced for C=S
molecular orbitals relative to C=O.
[Sustmann, R.; Sicking, W.; Huisgen, R. "A Computational Study of the Cycloaddition of Thiobenzophenone S-Methylide to Thiobenzophenone". J. Am. Chem. Soc. 2003, 125, 14425-14434. ] The striking blue appearance of thiobenzophenone is attributed to
π→ π* transitions upon the absorption of red light.
Thiocamphor is red.
Preparative methods
Thiones are usually prepared from ketones using reagents that exchange S and O atoms. A common reagent is
phosphorus pentasulfide
Phosphorus pentasulfide is the inorganic compound with the formula (empirical) or ( molecular). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in ...
, although that reagent also tends to induce side-reactions.
[ ]Lawesson's reagent
Lawesson's reagent (LR) is a chemical compound used in organic synthesis as a thiation agent. Lawesson's reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a sy ...
is related. Other methods uses a mixture of hydrogen chloride
The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...
combined with hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
. Bis(trimethylsilyl)sulfide has also been employed.[ Thiones can also be prepared from geminal dichlorides,] but geminal dichlorides are typically prepared from ketones as well.
There are no general methods to oxidize methylene groups to thioketones,[ reflecting ]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 ...
's comparable electronegativity
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
to carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
.
Thiobenzophenone 6H5)2CS">C6H5)2CSis a stable deep blue
Blue is one of the three primary colours in the RYB color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical spe ...
compound that dissolves readily in organic solvents. It photooxidizes in air to benzophenone
Benzophenone is a naturally occurring organic compound with the formula (C6H5)2CO, generally abbreviated Ph2CO. Benzophenone has been found in some fungi, fruits and plants, including grapes. It is a white solid with a low melting point and ros ...
and sulfur. Since its discovery, a variety of related thiones have been prepared.
Thiosulfines
Thiosulfines, also called thiocarbonyl ''S''-sulfides, are compounds with the formula R2CSS. Although superficially appearing to be cumulene
A cumulene is a compound having three or more ''cumulative'' (consecutive) double bonds. They are analogous to allenes, only having a more extensive chain. The simplest molecule in this class is butatriene (), which is also called simply ''cumu ...
s, with the linkage R2C=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions. Thiosulfines are proposed to exist in equilibrium with dithiiranes, three-membered CS2 rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4- trithiolane (Ph2C)2S3, which arises via the cycloaddition of Ph2CSS to its parent Ph2CS.
External links and further reading
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*
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See also
* Thial, for a description of thioaldehydes.
* Thioketene
* Sulfene
* Selone (often called selenone)
References
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Functional groups