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Skeletal formula with numbering convention
Ball-and-stick model
Space-filling model
Preferred IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.000.075 Edit this at Wikidata
EC Number
  • 200-081-4
  • InChI=1S/C7H6N2/c1-2-4-7-6(3-1)8-5-9-7/h1-5H,(H,8,9) checkY
  • InChI=1/C7H6N2/c1-2-4-7-6(3-1)8-5-9-7/h1-5H,(H,8,9)
  • c1ccc2c(c1)[nH]cn2
Molar mass 118.139 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]
GHS labelling:
GHS07: Exclamation mark
H302, H315, H319, H335
P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.[2]


Benzimidazole is produced by condensation of o-phenylenediamine with formic acid,[3] 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.[4]


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.[5]

N,N'-Dialkylbenzimidazolium salts are precursors to certain N-heterocyclic carbenes.[6][7]


Benomyl is a fungicide with a benzimidazole core

Benzimidazole derivatives are among the most frequently used ring systems for small molecule drugs listed by the United States Food and Drug Administration.[8] 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.[citation needed]

Several dyes are derived from benzimidazoles.[9]

See also[edit]


  1. ^ Walba, Harold; Isensee, Robert W. (1961). "Acidity Constants of Some Arylimidazoles and Their Cations". The Journal of Organic Chemistry. 26 (8): 2789–2791. doi:10.1021/jo01066a039.
  2. ^ "Benzimidazole | CAMEO Chemicals | NOAA". Retrieved 2023-01-11.
  3. ^ E. C. Wagner, W. H. Millett (1939). "Benzimidazole". Organic Syntheses. 19: 12. doi:10.15227/orgsyn.019.0012.
  4. ^ Robert A. Smiley "Phenylene- and Toluenediamines" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_405
  5. ^ H. A. Barker; R. D. Smyth; H. Weissbach; J. I. Toohey; J. N. Ladd & 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. doi:10.1016/S0021-9258(18)69550-X. PMID 13796809.
  6. ^ R. Jackstell; A. Frisch; M. Beller; D. Rottger; M. Malaun; 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.
  7. ^ H. V. Huynh; J. H. H. Ho; T. C. Neo; 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.
  8. ^ Taylor, R. D.; MacCoss, M.; Lawson, A. D. G. J Med Chem 2014, 57, 5845.>
  9. ^ Horst Berneth "Methine Dyes and Pigments" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_487.pub2

Further reading[edit]

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