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Chemical compound
Benzimidazole is a heterocyclic aromatic organic compound. This bicyclic compound may be viewed as fused rings of the aromatic compounds benzene and imidazole. It is a white solid that appears in form of tabular crystals.
Preparation.
Benzimidazole was discovered during research on vitamin B12. The benzimidazole nucleus was found to be a stable platform on which drugs could be developed. Benzimidazole is produced by condensation of o-phenylenediamine with formic acid, or the equivalent trimethyl orthoformate:
C6H4(NH2)2 + HC(OCH3)3 → C6H4N(NH)CH + 3 CH3OH
2-Substituted derivatives are obtained when the condensation is conducted with aldehydes in place of formic acid, followed by oxidation.
Reactions.
Benzimidazole is a base:
C6H4N(NH)CH + H+ → [C6H4(NH)2CH]+
It can also be deprotonated with stronger bases:
C6H4N(NH)CH + LiH → Li [C6H4N2CH] + H2
The imine can be alkylated and also serves as a ligand in coordination chemistry. The most prominent benzimidazole complex features "N"-ribosyl-dimethylbenzimidazole, as found in vitamin B12. 
"N","N"'-Dialkylbenzimidazolium salts are precursors to certain "N"-heterocyclic carbenes.
Applications.
Benzimidazole derivatives are among the most frequently used ring systems for small molecule drugs listed by the United States Food and Drug Administration. Many pharmaceutical agents belong to the benzimidazole class of compounds. For example:
In printed circuit board manufacturing, benzimidazole can be used as an organic solderability preservative.
Several dyes are derived from benzimidazoles.
References.
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