“…1,2 In addition, aryl and heteroarylformazans obtained from the interaction of aryldiazonium salts with hydrazones are unstable in acid media, and the formation of products in this reaction is explained by elimination of the diazonium salts. [3][4][5] On the other hand, no evidence for the reversibility of the C-azo coupling reaction in the series of 'classical' azo compounds has so far been described in the literature.…”