Benzimidazole

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Benzimidazole
Skeletal formula with numbering convention
Ball-and-stick model Space-filling model
Identifiers
CAS number 51-17-2 YesY
PubChem 5798
ChemSpider 5593 YesY
UNII E24GX49LD8 YesY
KEGG C02009 YesY
ChEBI CHEBI:41275 YesY
ChEMBL CHEMBL306226 YesY
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C7H6N2
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]
Hazards
MSDS External MSDS
EU classification Harmful (Xn)
R-phrases R20 R21 R22 R36 R37 R38
S-phrases S26 S36
Except where noted otherwise, 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]

Preparation[edit]

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] 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]

References[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: 65 .

Further reading[edit]

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