ABSTRACT
The simple thiophenes are stable liquids which closely resemble the corresponding benzene compounds in boiling points and even in smell. Aromatic thiophenes play no part in animal metabolism; biotin, one of the vitamins, is a tetrahydrothiophene, however aromatic thiophenes do occur in some plants, in association with polyacetylenes with which they are biogenetically linked. Thiophene is stable to all but very strongly acidic conditions, so many reagent combinations which lead to acid-catalysed decomposition or polymerisation of furans and pyrroles are able to be applied successfully with thiophenes. Nitration of thiophene needs to be conducted in the absence of nitrous acid, which can lead to an explosive reaction; the use of acetyl nitrate or nitronium tetrafluoroborate are satisfactory. Simple thiophenes do not react with nucleophiles by addition or by substitution, though nitro-substituents activate the displacement of leaving groups like halide, as in benzene chemistry, and extensive use of this has been made in thiophene chemistry.
