2-Alkyl-1,2,3,4-benzotetrazinium Salts: Synthesis and NMR Studies of the Novel 2-Alkyl-1,2,3,4-tetrazinium/ortho-(Alkylazo)diazonium Equilibrium

Abstract

The diazotization of anilines bearing the ortho-alkylazo group resulted in benzenediazonium salts 3, which exist in equilibrium with the 2-alkyl-1,2,3,4-benzotetrazinium salt cyclic isomers 4. The structures of 3 and 4 were confirmed by 1H, 13C, and 15N NMR studies. The relative proportions of the cyclic and open-chain forms were determined by a 1H NMR study. The 3 ⇄ 4 equilibrium is fast on the NMR timescale, and only one set of signals is observed in the 1H and 13C NMR spectra. The equilibrium strongly depends on the substituents on the aromatic ring, while being practically unaffected by the substituents (methyl or tert-butyl) on the azo group. Some of the investigated salts exist only in the cyclic form (4f, 4g), others only in the open-chain form (3k). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)