It exists in two equivalent tautomeric forms, because hydrogen can be bound to one or the other nitrogen atom. Imidazole is a highly polar compound, as evidenced by its electric dipole moment of 3. Some resonance structures of imidazole are shown below: Amphoterism[ edit ] Imidazole is amphoteric. That is, it can function as both an acid and as a base.
|Published (Last):||17 November 2015|
|PDF File Size:||5.14 Mb|
|ePub File Size:||6.27 Mb|
|Price:||Free* [*Free Regsitration Required]|
It exists in two equivalent tautomeric forms, because hydrogen can be bound to one or the other nitrogen atom. Imidazole is a highly polar compound, as evidenced by its electric dipole moment of 3. Some resonance structures of imidazole are shown below: Amphoterism[ edit ] Imidazole is amphoteric. That is, it can function as both an acid and as a base. As an acid, the pKa of imidazole is The acidic proton is the one bound to nitrogen. Deprotonation gives the imidazole anion, which is symmetrical.
The basic site is the nitrogen with the lone pair and not bound to hydrogen. Protonation gives the imidazolium cation, which is symmetrical. Preparation[ edit ] Imidazole was first reported in by the German chemist Heinrich Debus , although various imidazole derivatives had been discovered as early as the s. It was shown that glyoxal , formaldehyde , and ammonia condense to form imidazole glyoxaline, as it was originally named.
In one microwave modification, the reactants are benzil , benzaldehyde and ammonia in glacial acetic acid , forming 2,4,5-triphenylimidazole "lophine". Many of these syntheses can also be applied to substituted imidazoles by varying the functional groups on the reactants. These methods are commonly categorized by the number of reacting components. Two component The 1,2 and 2,3 bonds can be formed by treating a 1,2-diamino alkane , at high temperatures, with an alcohol , aldehyde , or carboxylic acid.
A dehydrogenating catalyst, such as platinum on alumina , is required. The yield of this reaction is moderate, but it seems to be the most effective method of making the 1,4 substitution. Three component This method proceeds in good yields for substituted imidazoles. An adaptation of the Debus method, it is called the Debus-Radziszewski imidazole synthesis.
The starting materials are substituted glyoxal, aldehyde, amine, and ammonia or an ammonium salt. This reaction will give substantial yields only if the 1-vinyltetrazole is made efficiently from an organotin compound , such as 2-tributylstannyltetrazole. Imidazole can also be formed in a vapor-phase reaction. This forms a very pure imidazole product. The reaction has later been expanded to a two-step synthesis in which the aldimine is generated in situ: the Van Leusen Three-Component Reaction vL-3CR.
Biological significance and applications[ edit ] Imidazole is incorporated into many important biological molecules. The most pervasive is the amino acid histidine , which has an imidazole side-chain. Histidine is present in many proteins and enzymes and plays a vital part in the structure and binding functions of hemoglobin.
Imidazole-based histidine compounds play a very important role in intracellular buffering. Histamine can cause urticaria hives when it is produced during allergic reaction. The relationship between histidine and histamine is shown below: One of the applications of imidazole is in the purification of His-tagged proteins in immobilised metal affinity chromatography IMAC.
Imidazole is used to elute tagged proteins bound to nickel ions attached to the surface of beads in the chromatography column. An excess of imidazole is passed through the column, which displaces the His-tag from nickel coordination, freeing the His-tagged proteins. Imidazole has become an important part of many pharmaceuticals.
Synthetic imidazoles are present in many fungicides and antifungal , antiprotozoal , and antihypertensive medications. Imidazole is part of the theophylline molecule, found in tea leaves and coffee beans, that stimulates the central nervous system.
It is present in the anticancer medication mercaptopurine , which combats leukemia by interfering with DNA activities. A number of substituted imidazoles, including clotrimazole , are selective inhibitors of nitric oxide synthase , which makes them interesting drug targets in inflammation , neurodegenerative diseases and tumors of the nervous system. For comparison, another group of azoles is the triazoles, which includes fluconazole , itraconazole , and voriconazole. The difference between the imidazoles and the triazoles involves the mechanism of inhibition of the cytochrome P enzyme.
The N3 of the imidazole compound binds to the heme iron atom of ferric cytochrome P, whereas the N4 of the triazoles bind to the heme group. The triazoles have been shown to have a higher specificity for the cytochrome P than imidazoles, thereby making them more potent than the imidazoles.
It is instead a precursor to a variety of agrichemicals, including enilconazole , climbazole , clotrimazole , prochloraz , and bifonazole. Salts of imidazole[ edit ] Simple imidazolium cation Salts of imidazole where the imidazole ring is the cation are known as imidazolium salts for example, imidazolium chloride or nitrate. These salts have been used as ionic liquids and precursors to stable carbenes.
Salts where a deprotonated imidazole is an anion are also well known; these salts are known as imidazolates for example, sodium imidazolate, NaC3H3N2. Benzimidazole , an analog with a fused benzene ring Dihydroimidazole or imidazoline, an analog where 4,5- double bond is saturated Pyrrole , an analog with only one nitrogen atom in position 1 Oxazole , an analog with the nitrogen atom in position 1 replaced by oxygen Thiazole , an analog with the nitrogen atom in position 1 replaced by sulfur Pyrazole , an analog with two adjacent nitrogen atoms Triazoles , analogs with three nitrogen atoms.
Imidazole (Certified), Fisher Chemical
Appearance: light beige solid. Causes burns by all exposure routes. Harmful if swallowed. Possible risk of harm to the unborn child.