On the protonation and deuteration of 2-methylmercaptothiophene: Formation of a 2′,3′-dihydro-2,3′-bithiophene dimer

By dissolving 2‑methylmercaptothiophene (T) in trifluoracetic acid (TFA) a dimeric compound with a tetrahydrothiophene structure (HT5T4+) is formed and unambiguously indicated by appropriate 1H NMR and mass spectra. [Display omitted] 2‑Methylmercaptothiophene as heterocyclic thioanisole analogue is transformed by dissolving in trifluoracetic acid, instead into a S or C protonated species, into a dimeric compound with a tetrahydrothiophene unit. This finding has been derived from appropriate 1H NMR and mass spectra and stands in analogy to the oligomerisation of the parent thiophene with polyphosphoric acid.