Skeletal formula with numbering convention
Ball-and-stick model
Space-filling model
Preferred IUPAC name
Other names
51-17-2 YesY
3D model (Jmol) Interactive image
Interactive image
ChEBI CHEBI:41275 YesY
ChEMBL ChEMBL306226 YesY
ChemSpider 5593 YesY
ECHA InfoCard 100.000.075
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. It is a colorless solid.


Benzimidazole is produced by condensation of o-phenylenediamine with formic acid,[2] 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.this method afford 2-substituted benzimidazoles.[3]


Benzimidazole is a base:

C6H4N(NH)CH + H+ [C6H4(NH)2CH]+

It can also be deprotonated with stronger bases:

C6H4N(NH)CH + LiH Li [C6H4(NH)2CH] + 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.[4]

N,N'-Dialkylbenzimidazolium salts are precursors to certain N-heterocyclic carbenes.[5][6]


Benzimidazoles are often bioactive. Many anthelmintic drugs (albendazole, mebendazole, triclabendazole etc.) belong to the benzimidazole class of compounds. Benzimidazole fungicides are commercialized. They act by binding to the fungal microtubules and stopping hyphal growth. It also binds to the spindle microtubules and blocks nuclear division.

Benomyl (Benlate) is a fungicide with a benzimidazole core.


The benzimidazole opioid family includes a number of strong agents e.g. etonitazene, whose article discusses the family in some depth.[7]

In printed circuit board manufacturing, benzimidazole can be used as a organic solderability preservative.

Several dyes are derived from benzimidazoles.[8]

Benzimidazole is involved in the synthesis of the antiandrogen Galeterone.

See also


  1. Walba, H. & Isensee, R. W. Acidity constants of some arylimidazoles and their cations. J. Org. Chem. 26, 2789-2791 (1961).
  2. E. C. Wagner and W. H. Millett (1943). "Benzimidazole". Org. Synth.; Coll. Vol., 2, p. 65.
  3. Robert A. Smiley "Phenylene- and Toluenediamines" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_405
  4. 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. PMID 13796809.
  5. 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.
  6. 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.
  7. etonitzene
  8. 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

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