Thiophene

Thiophene
Identifiers
CAS number 110-02-1 Y
PubChem 8030
ChemSpider 7739 Y
UNII SMB37IQ40B Y
ChEBI CHEBI:30856 N
ChEMBL CHEMBL278958 Y
RTECS number XM7350000
Jmol-3D images Image 1
Properties
Molecular formula C4H4S
Molar mass 84.14 g/mol
Appearance colorless liquid
Density 1.051 g/mL, liquid
Melting point

−38 °C, 235 K, -36 °F

Boiling point

84 °C, 357 K, 183 °F

Refractive index (nD) 1.5287
Viscosity 0.8712 cP at 0.2 °C
0.6432 cP at 22.4 °C
Hazards
MSDS External MSDS
EU classification not listed
NFPA 704
3
2
0
Flash point −1 °C
Related compounds
Related thioethers Tetrahydrothiophene
Diethyl sulfide
Related compounds Furan
Pyrrole
 N (verify) (what is: Y/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromatic as indicated by its extensive substitution reactions. Related to thiophene are benzothiophene and dibenzothiophene, containing the thiophene ring fused with one and two benzene rings, respectively. Compounds analogous to thiophene include furan (C4H4O) and pyrrole (C4H4NH).

Contents

Isolation, occurrence

Thiophene was discovered as a contaminant in benzene.[1] It was observed that isatin forms a blue dye if it is mixed with sulfuric acid and crude benzene. The formation of the blue indophenin was long believed to be a reaction with benzene. Victor Meyer was able to isolate the substance responsible for this reaction from benzene. This new heterocyclic compound was thiophene.[2]

Thiophene and its derivatives occur in petroleum, sometimes in concentrations up to 1-3%. The thiophenic content of oil and coal is removed via the hydrodesulfurization (HDS) process. In HDS, the liquid or gaseous feed is passed over a form of molybdenum disulfide catalyst 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.

Synthesis and production

Reflecting their high stabilities, thiophenes arise from many reactions involving sulfur sources and hydrocarbons, especially unsaturated ones, e.g. acetylenes and elemental sulfur, which was the first synthesis of thiophene by Viktor Meyer in the year of its discovery. Thiophenes are classically prepared by the reaction of 1,4-diketones, diesters, or dicarboxylates with sulfiding reagents such as P4S10. Specialized thiophenes can be synthesized similarly using Lawesson's reagent as the sulfiding agent, or via the Gewald reaction, which involves the condensation of two esters in the presence of elemental sulfur. Another method is the Volhard-Erdmann cyclization.

Thiophene is produced on a scale of ca. 2M kg per year worldwide. Production involves the vapor phase reaction of a sulfur source, typically carbon disulfide, and butanol. These reagents are contacted with an oxide catalyst at 500–550 °C.[3]

Properties

At room temperature, thiophene is a colorless liquid with a mildly pleasant odor reminiscent of benzene, with which thiophene shares some similarities. The high reactivity of thiophene toward sulfonation is the basis for the separation of thiophene from benzene, which are difficult to separate by distillation due to their similar boiling points (4 °C difference at ambient pressure). Like benzene, thiophene forms an azeotrope with ethanol.

The molecule is flat; the bond angle at the sulphur is around 93 degrees, the C-C-S angle is around 109, and the other two carbons have a bond angle around 114 degrees. The C-C bonds to the carbons adjacent to the sulphur are about 1.34A, the C-S bond length is around 1.70A, and the other C-C bond is about 1.41A (figures from the Cambridge Structural Database).

Reactivity

Thiophene is considered aromatic, although theoretical calculations suggest that the degree of aromaticity is less than that of benzene. The "electron pairs" on sulfur are significantly delocalized in the pi electron system. As a consequence of its aromaticity, thiophene does not exhibit the properties seen for conventional thioethers. For example the sulfur atom resists alkylation and oxidation.

Toward electrophiles

Although the sulfur atom is relatively unreactive, the flanking carbon centers, the 2- and 5-positions, are highly susceptible to attack by electrophiles. Halogens give initially 2-halo derivatives followed by 2,5-dihalothiophenes; perhalogenation is easily accomplished to give C4X4S (X = Cl, Br, I).[4] Thiophene brominates 107 times faster than does benzene.[3]

Chloromethylation and chloroethylation occur readily at the 2,5-positions. Reduction of the chloromethyl product gives 2-methylthiophene. Hydrolysis followed by dehydration of the chloroethyl species gives 2-vinylthiophene.[5][6]

Desulfurization by Raney nickel

Desulfurization of thiophene with Raney nickel affords butane. When coupled with the easy 2,5-difunctionalization of thiophene, desulfurization provides a route to 1,4-disubstituted butanes.

Lithiation

Not only is thiophene reactive toward electrophiles, it is also readily lithiated with butyl lithium to give 2-lithiothiophene, which is a precursor to a variety of derivatives, including dithienyl.[7]

Coordination chemistry

Thiophene exhibits little thioether-like character, but it does serve as a pi-ligand forming piano stool complexes such as Cr(η5-C4H4S)(CO)3.[8]

Uses

Thiophenes are important heterocyclic compounds that are widely used as building blocks in many agrochemicals and pharmaceuticals.[3] The benzene ring of a biologically active compound may often be replaced by a thiophene without loss of activity.[9] This is seen in examples such as the NSAID lornoxicam, the thiophene analog of piroxicam.

Polythiophene

The polymer formed by linking thiophene through its 2,5 positions is called polythiophene. Polythiophene itself has poor processing properties. More useful are polymers derived from thiophenes substituted at the 3- and 3- and 4- positions. Polythiophenes become electrically conductive upon partial oxidation, i.e. they become "organic metals."[10]

References

  1. ^ Viktor Meyer (1883). "Ueber den Begleiter des Benzols im Steinkohlenteer". Berichte der Deutschen chemischen Gesellschaft 16: 1465–1478. doi:10.1002/cber.188301601324. http://gallica.bnf.fr/ark:/12148/bpt6k90696b/f1470.chemindefer. 
  2. ^ Ward C. Sumpter (1944). "The Chemistry of Isatin". Chemical Reviews 34 (3): 393–434. doi:10.1021/cr60109a003. 
  3. ^ a b c Jonathan Swanston “Thiophene” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2006. doi:10.1002/14356007.a26 793.pub2.
  4. ^ Henry Y. Lew and C. R. Noller (1963), "2-Iodolthiophene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV4P0545 ; Coll. Vol. 4: 545 
  5. ^ W. S. Emerson and T. M. Patrick, Jr. (1963), "2-Vinylthiophene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV4P0980 ; Coll. Vol. 4: 980 
  6. ^ K. B. Wiberg and H. F. McShane (1955), "2-Chloromethylthiophene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV3P0197 ; Coll. Vol. 3: 1 
  7. ^ E. Jones and I. M. Moodie (1988), "2-Thiophenethiol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV6P0979 ; Coll. Vol. 6: 979 
  8. ^ Rauchfuss, T. B., "The Coordination Chemistry of Thiophenes", Progress in Inorganic Chemistry 1991, volume 39, pp. 259-311. ISBN 978-0-471-54489-0
  9. ^ Daniel Lednicer (1999). The Organic Chemistry of Drug Synthesis. 6. New York: Wiley Interscience. pp. 187. ISBN 0-471-24510-0. 
  10. ^ J. Roncali (1992). "Conjugated poly(thiophenes): synthesis, functionalization, and applications". Chem. Rev. 92 (4): 711–738. doi:10.1021/cr00012a009. 

External links