Thioether


Thioether

A thioether (similar to "sulfide") is a functional group in organic chemistry that has the structure R1-S-R2 as shown on right. Like many other sulfur-containing compounds, volatile thioethers characteristically have foul odors. [R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0-471-95512-4.]

A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen. Because oxygen and sulfur belong to the chalcogens group in the periodic table, the chemical properties of ethers and thioethers share some commonalities. This functional group is important in biology, most notably in the amino acid methionine and the cofactor biotin.

Preparation

* Thioethers are typically prepared by the alkylation of thiols::R-Br + HS-R' → R-S-R' + HBrSuch 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, typically catalysed by free radicals::R-CH=CH2 + HS-R' → R-CH2-CH2-S-R'
* Thioethers can also be prepared via the Pummerer rearrangement.

Reactions

*While ethers are generally stable, thioethers (R-S-R) are easily oxidized to the sulfoxides (R-S(=O)-R), which can themselves be further oxidized to sulfones (R-S(=O)2-R). For example, dimethyl sulfide can be oxidized as follows::S(CH3)2 + OOS(CH3)2:OS(CH3)2 + OO2S(CH3)2Typical oxidants include peroxides.

*The sulfur-sulfur bond in disulfides 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-RThis reaction is exploited in biological systems as a means of transferring an alkyl group. For example, S-adenosylmethionine acts as a methylating agent in biological SN2 reactions.

*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 salts, such as trimethylsulfonium::S(CH3)2 + CH3I → [S(CH3)3] +I-

Thiophenes

The heterocyclic compound thiophene 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 π-system. Consequently thiophene exhibits few properties expected for a thioether - thiophene is non-nucleophilic at sulfur and, in fact, is sweet-smelling. Upon hydrogenation, thiophene gives tetrahydrothiophene, C4H8S, which indeed does behave as a typical thioether.

References


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Look at other dictionaries:

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  • thioéther — ● thioéther nom masculin Nom générique des composés de formule générale R―S―R′, analogues soufrés des éthers ROR′. (On les emploie en synthèse organique et pour odoriser le gaz naturel.) …   Encyclopédie Universelle

  • Thioether — Allgemeine Struktur eines Thioethers Thioether sind organische Sulfide, also in der Chemie eine Stoffgruppe mit der allgemeinen Struktur R1−S−R2, wobei R1 und R2 organische Reste sind. Sie sind die Schwefelanaloga der Ether. Die von Alkanen… …   Deutsch Wikipedia

  • Thioéther — Les thioéthers sont les équivalents sulfurés des éther oxydes. Dans ces composés les deux groupes alkyles sont reliés par un atome de soufre, et non plus par un atome d oxygène. On les obtient par la condensation de deux thiols. Parmi les… …   Wikipédia en Français

  • thioether — The bond R S C, of which the best example is in methionine …   Dictionary of molecular biology

  • thioether — noun any analogue of an ether, or general formula RSR, in which the oxygen has been replaced by sulfur; an organic sulfide …   Wiktionary

  • thioether — An organic sulfide; an ether in which the oxygen is replaced by sulfur; R S R′. * * * thio·ether ē thər n a compound analogous to ether in which the oxygen has been replaced by sulfur * * * thio·ether (thi″o eґthər) a sulfur ether; an… …   Medical dictionary

  • Thioether — Thio|ether 〈m. 3; fachsprachl.〉 = Thioäther * * * Thi|o|e|ther [↑ Ether (1)], der; s, : veraltete Bez. für org. Sulfide …   Universal-Lexikon

  • thioether — thio·ether …   English syllables

  • thioether — |thīō+ noun Etymology: International Scientific Vocabulary thi + ether : sulfide 2 …   Useful english dictionary


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