1.2.3- Triazoles bromination nitration

Among tetraazapentalenes, early work by Pfleger et a/.350 on 2,6-dimethyl-y-triazolo[2,l-a]-y-triazole 447 showed that mono- and di-substituted products were formed. Bromination, nitration, and benzoyl-ation lead to 3,7-disubstitution, whereas 3-monosubstitution resulted from nitrosation, acetylation, carbethoxylation, and diazotization. Iodin-... 

Furthermore, the electron-attracting triazole ring was found to facilitate the removal of bromine (but not of chlorine) during nitration thus, D-arobmo-hexose ( n-glucose ) (p-bromophenyl)osotriazole tetraacetate, when nitrated, gives D-arabino-hexose (p-nitrophenyl)osotriazole tetraacetate. ... 

Electrophilic substitution at carbon, e.g. nitration and sulfonation, proceed very slowly. The action of chlorine or bromine leads to (3)5-chloro- or 3(5)-bromo-1,2,4-triazole by way of 1-halo intermediates ... 

Methyl-1,2,3-triazole can be brominated at C-4, but the 2-methyl isomer is less reactive, requiring the use of an iron catalyst the lower reactivity of the latter is probably related to the presence of two azomethine units. Nitration of 2-phenyl-1,2,3-triazole proceeds first on the benzene ring, but then does bring about hetero-ring substitution. ... 

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