Benzimidazole
O-Phenylenediamine
Formic acid
Orthoformic acid

https://en.m.wikipedia.org/wiki/Benzimidazole

https://en.m.wikipedia.org/wiki/O-Phenylenediamine

https://en.m.wikipedia.org/wiki/Formic_acid

https://en.m.wikipedia.org/wiki/Orthoformic_acid

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https://labmonk.com/synthesis-of-benzimidazole-from-o-phenylenediamine

https://www.researchgate.net/publication/289087006_Green_Synthesis_of_Benzimidazole_Derivatives_An_Overview_of_Bulk_Drug_Synthesis

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The two (carbon)-(nitrogen) bonds in benzimidazole when disconnected give o-phenylenediamine and formic acid.

O-Phenylenediamine

O (Phenylene)-(Diamine)

2-nitro-chloro-benzeneis treated with ammonia and the resulting 2-(amino)-(nitro)-(benzene) is then (hydrogen)ated:

ClC6H4NO2 + 2 NH3 → H2NC6H4NO2 + NH4ClH2NC6H4NO2 + 3 H2 → H2NC6H4NH2 + 2 H2O

the reduction of the nitro-(aniline) is effected with (zinc) powder in ethanol, followed by purification of the (diamine) as the hydro-chloride (salt).

This compound darkens in air; impurities may be removed by treating a hot aqueous solution with sodium dithionite reducing agent and activated carbon, and allowing the product to cool crystallize.

Synthesis of Nitrogen, Oxygen and Sulphur containing heterocyclic have appeared owing to a wide variety of their biological activity. In recent years, numerous reports concerning the synthesis of heterocyclic compounds under various conditions like solvent-free, reactants immobilized on solid support, microwave irradiation condition, green catalyst and green solvent have appeared. Benzimidazole is a heterocyclic aromatic organic compound.