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Thioether
 
 
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A thioether (similar to sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
) is a functional group in organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
 that has the structure R1-S-R2 as shown on right. Like many other sulfur-containing compounds, volatile
Volatile organic compound

Volatile organic compounds are organic chemical compounds that have high enough vapor pressures under normal conditions to significantly vaporize and enter the atmosphere....
 thioethers characteristically have foul odors.

A thioether is similar to an ether
Ether

Ether is a class of organic compounds which contain an ether functional group ? an oxygen atom connected to two alkyl or aryl groups ? of general formula R?O?R....
 except that it contains a sulfur atom in place of the oxygen. Because oxygen and sulfur belong to the chalcogen
Chalcogen

The chalcogens are the Chemical element in periodic table group 16 of the periodic table. It is sometimes known as the oxygen family. It consists of the chemical element oxygen , sulfur , selenium , tellurium , the radioactive element polonium , and the synthetic element ununhexium ....
s group in the periodic table
Periodic table

The periodic table of the chemical elements is a table method of displaying the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869....
, the chemical properties of ethers and thioethers share some commonalities.






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A thioether (similar to sulfide
Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
) is a functional group in organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
 that has the structure R1-S-R2 as shown on right. Like many other sulfur-containing compounds, volatile
Volatile organic compound

Volatile organic compounds are organic chemical compounds that have high enough vapor pressures under normal conditions to significantly vaporize and enter the atmosphere....
 thioethers characteristically have foul odors.

A thioether is similar to an ether
Ether

Ether is a class of organic compounds which contain an ether functional group ? an oxygen atom connected to two alkyl or aryl groups ? of general formula R?O?R....
 except that it contains a sulfur atom in place of the oxygen. Because oxygen and sulfur belong to the chalcogen
Chalcogen

The chalcogens are the Chemical element in periodic table group 16 of the periodic table. It is sometimes known as the oxygen family. It consists of the chemical element oxygen , sulfur , selenium , tellurium , the radioactive element polonium , and the synthetic element ununhexium ....
s group in the periodic table
Periodic table

The periodic table of the chemical elements is a table method of displaying the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869....
, the chemical properties of ethers and thioethers share some commonalities. This functional group is important in biology, most notably in the amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
 methionine
Methionine

Methionine is an a-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This Essential amino acid is classified as nonpolar....
 and the cofactor
Cofactor

Cofactor may refer to any of the following:* Cofactor The signed minor of a matrix* Minor as an alternative name for the determinant of a smaller Matrix than that which it describes...
 biotin
Biotin

Biotin, also known as vitamin H or B7, has the chemical formula C10H16N2O3S , is a water-soluble B-complex vitamin which is composed of an ureido ring fused with a tetrahydrothiophene ring....
.

Preparation

  • Thioethers are typically prepared by the alkylation
    Alkylation

    Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene ....
     of thiol
    Thiol

    In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom . Being the sulfur analogue of an alcohol group , this functional group is referred to either as a thiol group or a sulfhydryl group....
    s:
R-Br + HS-R' ? R-S-R' + HBr
Such reactions are accelerated in the presence of base, which converts the thiol into the more nucleophilic thiolate.
  • An alternative method of synthesis includes the addition of a thiol to an alkene
    Alkene

    In organic chemistry, an alkene, olefin, or olefine is an Saturation chemical compound containing at least one carbon-to-carbon double bond....
    , typically catalysed by free radicals:
R-CH=CH2 + HS-R' ? R-CH2-CH2-S-R'
  • Thioethers can also be prepared via the Pummerer rearrangement
    Pummerer rearrangement

    The Pummerer rearrangement is an organic reaction whereby an alkyl sulfoxide rearrangement reaction to an a-acyloxy-thioether in the presence of acetic anhydride....
    .


Reactions

  • While ethers are generally stable, thioethers (R-S-R) are easily oxidized to the sulfoxide
    Sulfoxide

    A sulfoxide is a chemical compound containing a sulfinyl functional group attached to two carbon atoms. Sulfoxides can be considered as oxidized thioether....
    s (R-S(=O)-R), which can themselves be further oxidized to sulfone
    Sulfone

    A sulfone is a chemical compound containing a sulfonyl functional group attached to two carbon atoms. The central sulfur atom is twice double bonded to oxygen and has two further hydrocarbon substituents....
    s (R-S(=O)2-R). For example, dimethyl sulfide
    Dimethyl sulfide

    Dimethyl sulfide or methylthiomethane is an Organosulfur compounds compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at 37?C and has a characteristic disagreeable odor....
     can be oxidized as follows:
S(CH3)2 + O
O

O is the fifteenth letter of the modern Latin alphabet. Its name in English language is spelled o , plural oes ....
 ? OS(CH3)2
Dimethyl sulfoxide

Dimethyl sulfoxide is the chemical compound with the chemical formula 2SO. It was first synthesized in 1866 by the Russian scientist Alexander Saytzeff, who reported his findings in a German chemistry journal in 1867....
OS(CH3)2 + O
O

O is the fifteenth letter of the modern Latin alphabet. Its name in English language is spelled o , plural oes ....
 ? O2S(CH3)2
Methylsulfonylmethane

Methylsulfonylmethane , also known as dimethyl sulfone, is an organosulfur compound with the chemical formula 2SO2. This colourless solid features the sulfone functional group and is considered relatively inert chemically....
Typical oxidants include peroxide
Peroxide

A peroxide is a compound containing an oxygen-oxygen chemical bond. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately....
s.

  • The sulfur-sulfur bond in disulfide
    Disulfide

    In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. The disulfide anion is S22-....
    s is susceptible to cleavage by nucleophiles, and reaction with a carbon nucleophile produces a thioether:
R3C- + R1S-SR2 ? R3CSR1 + R2S-


  • Trialkysulfonium salts react with nucleophiles with a dialkyl sulfide as a leaving group:
Nu- + R3S+ ? Nu-R + R-S-R
This reaction is exploited in biological systems as a means of transferring an alkyl group
Alkyl

An alkyl is a univalent Radical consisting of carbon and hydrogen atoms, arranged in a chain. The Alkyls form homologous series with the general formula CnH2n+1....
. For example, S-adenosylmethionine
S-Adenosyl methionine

S-Adenosyl methionine is a coenzyme involved in methyl group transfers. SAM was first discovered in Italy by G. L. Cantoni in 1952. It is made from adenosine triphosphate and methionine by methionine adenosyltransferase ....
 acts as a methylating agent
Methylation

Methylation in the chemical sciences denotes the attachment or substitution of a methyl on various Substrate . This term is commonly used in chemistry, biochemistry, soil science and the biological sciences....
 in biological SN2 reactions
SN2 reaction

The SN2 reaction is a type of nucleophilic substitution, where a lone pair from a nucleophile attacks an electron deficient electrophile center and covalent bond to it, expelling another group called a leaving group....
.

  • Ethers can be alkylated at oxygen only with difficulty to give highly reactive trialkyloxonium salts. In contrast, thioethers are readily alkylated to give stable sulfonium
    Sulfonium

    A sulfonium ion, also known as sulphonium ion and sulfanium ion, is a positively charged sulfur ion carrying three alkyl functional group as Substitution ....
     salts, such as trimethylsulfonium:
S(CH3)2 + CH3I ? [S(CH3)3]+I-


Thiophenes

The heterocyclic compound
Heterocyclic compound

Heterocyclic compounds are organic compounds containing at least one atom of carbon, and at least one element other than carbon, such as sulfur, oxygen or nitrogen within a ring structure....
 thiophene
Thiophene

Thiophene is the heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromaticity as indicated by its extensive substitution reactions....
 is formally a thioether. Because of the aromatic character of this heterocycle, the nonbonding electrons on sulfur, normally responsible for the nucleophilicity so characteristic of thioethers, are delocalized into the p-system. Consequently thiophene exhibits few properties expected for a thioether - thiophene is non-nucleophilic at sulfur and, in fact, is sweet-smelling. Upon hydrogenation
Hydrogenation

Hydrogenation is the chemical reaction that results from the addition of hydrogen . The process is usually employed to a redox or Saturation organic compounds....
, thiophene gives tetrahydrothiophene
Tetrahydrothiophene

Tetrahydrothiophene is a heterocyclic organic compound consisting of a five-membered ring containing four carbon atoms and a sulfur atom. It is the saturation analog of thiophene....
, C4H8S, which indeed does behave as a typical thioether.