Polarographic reduction and tautomeric structure of 2‐amino‐5‐arylazothiazoles

The polarographic behaviour of a series of 2‐amino‐4‐phenyl‐5‐arylazothiazoles has been investigated at a dropping mercury electrode. Each of the compounds studied exhibits one wave which was shown to correspond to the reductive cleavage of the azo linkage by a 4e irreversible step. On the basis of the polarographic data, it was concluded that the compounds exist only in one tautomeric form, namely the aminoazo structure 1 . The results of E 1/2 — σ X correlations and HMO calculations of bonding energies of the various possible tautomeric forms 1–3 indicate that the aminoazo form 1 is the most stable structure of the compounds examined.