Thiophenesulfonic acids

In —I—M-substituted aminothiophenes, the possibility of coupling during diazotization is eliminated. Thus ethyl 5-amino-2-thiophene-carboxylate and 5-amino-2-thiophenesulfonic acid and its amide- have been diazotized and coupled with various reagents. 

In 1883, Viktor Meyer first detected thiophene in coke-oven benzole, where it is present in concentrations of around 1%. (Because of the close relationship between thiophene and benzene, Meyer took the name kryptophen ( hidden in benzene ) into consideration.) Recovery of thiophene from coke-oven benzole, which is possible by the reaction of thiophene with concentrated sulfuric acid to thiophenesulfonic acid, is not used industrially since the synthesis is more economical. 

In general, one anion is incorporated for every three pyrrole units. Exceptions are pyrrole- or thiophenesulfonic acids where the counterion is coupled directly to the monomer (self doping) [55]. Some typical conducting anions are fluoroborate, perchlorate, aromatic sulfonic acids, penicillin, -dodecyl sulfate phthalocyanine sulfonic acid, poly(styrenesulfonicacid), styrene sulfonic acid, and heparin [13]. 

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