Thiophenes

Thiophene

Names
Preferred IUPAC name Thiophene
Other names Thiofuran Thiacyclopentadiene Thiole
Identifiers
CAS Number	110-02-1 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30856 Y
ChemSpider	7739 Y
ECHA InfoCard	100.003.392
PubChem CID	8030
RTECS number	XM7350000
UNII	SMB37IQ40B Y
InChI InChI=1S/C4H4S/c1-2-4-5-3-1/h1-4H Y Key: YTPLMLYBLZKORZ-UHFFFAOYSA-N Y InChI=1/C4H4S/c1-2-4-5-3-1/h1-4H Key: YTPLMLYBLZKORZ-UHFFFAOYAY
SMILES c1ccsc1
Properties
Chemical formula	C4H4S
Molar mass	84.14 g/mol
Appearance	colorless liquid
Density	1.051 g/mL, liquid
Melting point	−38 °C (−36 °F; 235 K)
Boiling point	84 °C (183 °F; 357 K)
Magnetic susceptibility (χ)	-57.38·10−6 cm3/mol
Refractive index (nD)	1.5287
Viscosity	0.8712 cP at 0.2 °C 0.6432 cP at 22.4 °C
Hazards
Safety data sheet	External MSDS, External MSDS
EU classification (DSD) (outdated)	not listed
NFPA 704	3 2
Flash point	−1 °C (30 °F; 272 K)
Related compounds
Related thioethers	Tetrahydrothiophene Diethyl sulfide
Related compounds	Furan Pyrrole
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Thiophene is a heterocyclic compound with the formula C₄H₄S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reactions, it resembles benzene. Compounds analogous to thiophene include furan (C₄H₄O) and pyrrole (C₄H₄NH), which each vary by the heteroatom in the ring.

Thiophene was discovered as a contaminant in benzene. It was observed that isatin (an indole) forms a blue dye if it is mixed with sulfuric acid and crude benzene. The formation of the blue indophenin had long been believed to be a reaction of benzene itself. Viktor Meyer was able to isolate thiophene as the actual substance responsible for this reaction.

Thiophene and especially 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.

Reflecting their high stabilities, thiophenes arise from many reactions involving sulfur sources and hydrocarbons, especially unsaturated ones. The first synthesis of thiophene by Meyer, reported the same year that he reported its discovery, involve acetylene and elemental sulfur. Thiophenes are classically prepared by the reaction of 1,4-diketones, diesters, or dicarboxylates with sulfidizing reagents such as P₄S₁₀ such as in the Paal-Knorr thiophene synthesis. Specialized thiophenes can be synthesized similarly using Lawesson's reagent as the sulfidizing 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.