Isolation, Occurrence
Thiophene was discovered as a contaminant in benzene. 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.
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.
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