Thiophene

From Wikipedia, the free encyclopedia

Thiophene

General
Systematic name	Thiophene
Other names	Thiofuran Thiacyclopentadiene
Molecular formula	C₄H₄S
SMILES	C1=CC=CS1
Molar mass	84.14 g/mol
Appearance	colorless liquid
CAS number	[110-02-1]
Properties
Density and phase	1.051 g/ml, liquid
Solubility	Immiscible with water soluble in most organic solvents
Melting point	−38 °C
Boiling point	84 °C
Viscosity	? cP at ? °C
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	not listed
NFPA 704	3 2 0
Flash point	−1 °C
RTECS number	XM7350000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related thioethers	Tetrahydrothiophene Diethyl sulfide
Related compounds	Furan Pyrrole
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Thiophene is an aromatic heterocyclic compound consisting of four carbon atoms and one sulfur atom in a five-membered ring. Compounds analogous to thiophene include furan and pyrrole where the S atom is replaced by O and NH, respectively. Thiophene was discovered by Viktor Meyer in 1871 as a contaminant in benzene. Related to thiophene are benzothiophene and dibenzothiophene, containing the thiophene ring fused with one and two benzene rings, respectively.

1 Properties
2 Uses
3 Synthesis and occurrence
4 See also
5 External links

[edit] Properties

At room temperature, thiophene is a colorless liquid with a mildly pleasant odor reminiscent of benzene, with which thiophene shares some similarities.

Thiophene is considered aromatic, although theoretical calculations suggest that the degree of aromaticity is less than that of benzene. The participation of the lone electron pairs on sulfur in the delocalized pi electron system is significant. As a consequence of its aromaticity, thiophene does not exhibit the properties seen for conventional thioethers. For example the sulfur atom is not alkylated by methyl iodide. Although the sulfur atom is unreactive, the flanking CH centers are susceptible to attack by electrophiles. The high reactivity of thiophene toward sulfonation is the basis for the separation of thiophene from benzene. Due to the mere 4 °C difference in their boiling points at ambient pressure, thiophene and benzene are difficult to separate by distillation. Treatment of thiophene-benzene mixtures with sulfuric acid results in preferential sulfonation of the thiophene to give water-soluble thiophene sulfonic acid.

[edit] Uses

Thiophenes are important heterocyclic compounds and are recurring building blocks in organic chemistry with applications in pharmaceuticals. For example, thiophenes are used as synthetic intermediates, taking advantage of the susceptability of the carbon atoms adjacent to S toward electrophilic reactions. Desulfurization of the resulting ring using Raney nickel affords 1,4-disubstituted butanes. The polymer formed by linking thiophene through its 1,5 positions is called polythiophene. Polythiophenes become electrically conductive upon partial oxidation, i.e. they become "organic metals".

Thiophene is used as a denaturant for ethanol with which it forms an azeotrope.

[edit] Synthesis and occurrence

Reflecting their high stabilities, thiophenes arise from many reactions involving sulfur sources and hydrocarbons, especially unsaturated ones, e.g. acetylenes and elemental sulfur. Thiophenes are classically prepared by the reaction of 1,4-diketones with sulfiding reagents such as Lawesson's reagent or P₄S₁₀. Specialized thiophenes can be synthesized via the Gewald reaction, which involves the condensation of two esters in the presence of elemental suflur.

Thiophene and its derivatives occur in petroleum, sometimes in concentrations up to 1-3 %. The thiophenic content of liquids from oil and coal is removed via the hydrodesulfurization (HDS) process. In HDS, the liquid or gaseous feed is passed over a special form of molybdenum disulfide under a pressure of H₂. Thiophenes undergo hydrogenolysis to form hydrocarbons and hydrogen sulfide. Thus, thiophene itself is converted to butane and H₂S. More prevalent and more problematic in petroleum are benzothiophene and dibenzothiophene.

[edit] See also

Pyrrole, an analog with a NH instead of the sulfur atom.
Furan, an analog with an oxygen instead of the sulfur atom.
Simple aromatic rings

[edit] External links

International Chemical Safety Card 1190
[1] Roncali, J., "Conjugated Poly(thiophenes): Synthesis, Functionalization, and Applications", Chemical Reviews, 1992, v. 92, p 711-738.