Benzimidazole

Chembox new
ImageFile = Benzimidazole chemical structure.png ImageSize =
IUPACName = 1H-benzimidazole
OtherNames =
Section1 = Chembox Identifiers
CASNo = 51-17-2
PubChem = 5798
SMILES = c1cccc2ncnc12
Section2 = Chembox Properties
C=7|H=6|N=2
Appearance =
Density =
MeltingPt = 170-172 °C
BoilingPt =
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Section3 = Chembox Hazards
ExternalMSDS = [http://msds.chem.ox.ac.uk/BE/benzimidazole.html External MSDS]
EUClass = Harmful (Xn)
RPhrases = R20 R21 R22 R36 R37 R38
SPhrases = S26 S36
FlashPt =
Autoignition =

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. [cite journal
author = H. A. Barker, R. D. Smyth, H. Weissbach, J. I. Toohey, J. N. Ladd, and B. E. Volcani
title = Isolation and Properties of Crystalline Cobamide Coenzymes Containing Benzimidazole or 5,6-Dimethylbenzimidazole
journal = Journal of Biological Chemistry
year = 1960
volume = 235
issue = 2
pages = 480–488
url = http://www.jbc.org/cgi/reprint/235/2/480 ]

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. [cite journal | author = R. Jackstell, A. Frisch, M. Beller, D. Rottger, M. Malaun and B. Bildstein | title = Efficient telomerization of 1,3-butadiene with alcohols in the presence of in situ generated palladium(0)carbene complexes | year = 2002 | journal = | volume = 185 | issue = 1-2 | pages = 105–112 | doi = 10.1016/S1381-1169(02)00068-7] [cite journal | author = H. V. Huynh, J. H. H. Ho, T. C. Neo and L. L. Koh | title = Solvent-controlled selective synthesis of a trans-configured benzimidazoline-2-ylidene palladium(II) complex and investigations of its Heck-type catalytic activity | year = 2005 | journal = Journal of Organometallic Chemistry | volume = 690 | issue = 16 | pages = 3854–3860 | doi = 10.1016/j.jorganchem.2005.04.053]

Preparation

Benzimidazole is commercially available. The usual synthesis involves condensation of o-phenylenediamine with formic acid,OrgSynth | title = Benzimidazole | prep = cv2p0065 | collvol = 2 | collvolpages = 65 | year = 1943 | author = E. C. Wagner and W. H. Millett] 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.

See also

* Albendazole, a common use anthelmintic.
* Indole, an analog with CH in place of nitrogen in position 3.
* Purine, an analog with two additional nitrogen atoms in the six-membered ring.
* Simple aromatic rings
* Triclabendazole, most common drug against liver flukes

References

Further reading

*cite book |author=Grimmett, M. R. |title=Imidazole and benzimidazole synthesis |publisher=Academic Press |location=Boston |year=1997 |pages= |isbn=0-12-303190-7 |oclc= |doi= |accessdate=