Thiophene is a heterocyclic compound with the chemical formula C4H4S.It consists of a planar five-membered ring, which is aromatic as indicated by its extensive substitution reactions.It is a colorless liquid with a benzene-like odor.It is similar to benzene in most reactions. Compounds similar to thiophene include furan (C4H4O), selenophene (C4H4Se) and pyrrole (C4H4NH), each of which varies by the heteroatom in the ring.
Isolation and occurrence
Thiophene was found to be a contaminant in benzene.It was observed that isatin (an indole) forms a blue dye if mixed with sulfuric acid and crude benzene.The formation of blue indoxyl has long been thought to be a reaction of benzene itself.Thiophene, especially its derivatives is present in petroleum, sometimes in concentrations as high as 1–3%.The thiophene content in oil and coal is removed by the hydrodesulfurization (HDS) process.In HDS, a liquid or gaseous feed is passed over a form of molybdenum disulfide catalyst under H2 pressure.Thiophene undergoes hydrogenolysis to form hydrocarbons and hydrogen sulfide.Thus, thiophene itself is converted to butane and H2S.More prevalent and problematic in petroleum are benzothiophenes and dibenzothiophenes.
At room temperature, thiophene is a colorless liquid with a mild, pleasant odor reminiscent of benzene,bearing some resemblance to thiophene.The high reactivity of thiophene to sulfonation is the basis for the separation of thiophene from benzene, which is 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 sulfur bond angle is about 93°, the C-C-S angle is about 109°, and the other two carbons are about 114°.The C-C bond of the carbon adjacent to sulfur is about 1.34 Å, the length of the C-S bond is about 1.70 Å, and the other C-C bond is about 1.41 Å.