Chemistry of polyhalogenodiazabutadienes. Part IV. The synthesis of dihalogeno- and trihalogeno-diazabutadienes

Abstract

Reaction of arylmethylene(tetrazol-5-yl)hydrazines (VI) with bromine in aqueous acetic acid leads to tetrazolyl ring cleavage with formation of the 1,1-dibromo-2,3-diazabutadienes (ArCH:N·N:CBr₂)(II). This reaction involves initial N-bromination, loss of HBr to give a tetrazol-5-ylidenehydrazine (XII), followed by production of an arylmethyleneamino-isocyanide (ArCH:N·NC), which adds bromine to yield the 4-aryl-1,1-dibromo-2,3-diazabutadienes (II). Chlorination of the hydrazines (VI) in aqueous acetic acid yields the 1,1,4-trichloro-2,3-diazabutadienes (ArCCl:N·N:CCl₂)(IV), via the intermediate hydrazonyl chlorides (VII). The corresponding tribromo-compounds (V) are prepared similarly, through the intermediacy of the hydrazonyl bromides (VIII). The tribromides cannot be prepared from the dibromodiazabutadienes (II).