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Skeletal formula with numbering convention
Ball-and-stick model
Space-filling model
IUPAC name
51-17-2 YesY
ChEBI CHEBI:41275 YesY
ChEMBL ChEMBL306226 YesY
ChemSpider 5593 YesY
Jmol interactive 3D Image
KEGG C02009 YesY
PubChem 5798
Molar mass 118.14 g·mol−1
Melting point 170 to 172 °C (338 to 342 °F; 443 to 445 K)
Acidity (pKa) 12.8 (for benzimidazole) and 5.6 (for the conjugate acid) [1]
Safety data sheet External MSDS
Harmful (Xn)
R-phrases R20 R21 R22 R36 R37 R38
S-phrases S26 S36
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzimidazole is a heterocyclic aromatic organic compound. This bicyclic compound consists of the fusion of benzene and imidazole. The most prominent benzimidazole compound in nature is N-ribosyl-dimethylbenzimidazole, which serves as an axial ligand for cobalt in vitamin B12.[2]

Benzimidazole, in an extension of the well-elaborated imidazole system, has been used as carbon skeletons for N-heterocyclic carbenes. The NHCs are usually used as ligands for transition metal complexes. They are often prepared by deprotonating an N,N'-disubstituted benzimidazolium salt at the 2-position with a base.[3][4]


Benzimidazole is commercially available. The usual synthesis involves condensation of o-phenylenediamine with formic acid,[5] or the equivalent trimethyl orthoformate:

C6H4(NH2)2 + HC(OCH3)3 → C6H4N(NH)CH + 3 CH3OH

By altering the carboxylic acid used, this method is generally able to afford 2-substituted benzimidazoles.[5]


Many anthelmintic drugs (albendazole, mebendazole, triclabendazole etc.) belong to the benzimidazole class of compounds.

Benzimidazole also has fungicidal properties. It acts by binding to the fungal microtubules and stopping hyphal growth. It also binds to the spindle microtubules and blocks nuclear division.

See also[edit]


  1. ^ Walba, H. & Isensee, R. W. Acidity constants of some arylimidazoles and their cations. J. Org. Chem. 26, 2789-2791 (1961).
  2. ^ H. A. Barker, R. D. Smyth, H. Weissbach, J. I. Toohey, J. N. Ladd, and B. E. Volcani (February 1, 1960). "Isolation and Properties of Crystalline Cobamide Coenzymes Containing Benzimidazole or 5,6-Dimethylbenzimidazole". Journal of Biological Chemistry 235 (2): 480–488. PMID 13796809. 
  3. ^ R. Jackstell, A. Frisch, M. Beller, D. Rottger, M. Malaun and B. Bildstein (2002). "Efficient telomerization of 1,3-butadiene with alcohols in the presence of in situ generated palladium(0)carbene complexes". Journal of Molecular Catalysis A: Chemical 185 (1–2): 105–112. doi:10.1016/S1381-1169(02)00068-7. 
  4. ^ H. V. Huynh, J. H. H. Ho, T. C. Neo and L. L. Koh (2005). "Solvent-controlled selective synthesis of a trans-configured benzimidazoline-2-ylidene palladium(II) complex and investigations of its Heck-type catalytic activity". Journal of Organometallic Chemistry 690 (16): 3854–3860. doi:10.1016/j.jorganchem.2005.04.053. 
  5. ^ a b E. C. Wagner and W. H. Millett (1943). "Benzimidazole". Org. Synth. ; Coll. Vol. 2, p. 65 .

Further reading[edit]

  • Grimmett, M. R. (1997). Imidazole and benzimidazole synthesis. Boston: Academic Press. ISBN 0-12-303190-7.