Unlike the 1,2-diaminobenzimidazole which
underwent condensation with aromatic aldehydes only
at the N-amino group [10], hydrazine I reacted at once
with 2 mol of aldehyde forming hydrazones II.
Analogously, e.g., to 4-amino-3-hydrazino-1,2,4-tria-oline-5-thione the product of this reaction may be
tetrazinobenzimidazole III [11], yet in this case the
results of the elemental analysis and the 1Н NMR
spectrum of the compound unambiguously prove the
composition and the structure of heterocycle II