288-32-4

chemical properties

Imidazole is between the two nitrogen atoms of five membered heterocyclic compounds containing. The unshared electron pair of 1-bit nitrogen atom in imidazole ring participates in the cyclic conjugation, reduces the electron density of the nitrogen atom, and makes hydrogen of the nitrogen atom easily leave in the form of hydrogen. Therefore imidazole has weak acidity, and can form salt with strong base. The unshared electron pair of 3-bit nitrogen atom in imidazole ring doesn’t participates in the cyclic conjugation, while it occupies the sp2 hybridized orbital, can accept protons, and form salt with strong acid. Alkaline of imidazole is slightly stronger than pyrazole and pyridine. There is tautomerism in the imidazole ring. The hydrogen on the 1-bit nitrogen atom can be transferred to the 3-atom, therefore, imidazole derivatives with same substituent respectively on 4-bit and 5-bit are tautomers. Imidazole is stable to acid, and has antioxidant activity. Imidazole derivatives are widely found in nature, such as histamine, histidine and benzimidazole, etc. There are some interesting reagents in acyl imidazole compounds. For example, 1-acetyl imidazole is a stable acylating agent, after reaction with pyrrole, it becomes 1-acetyl pyrrole. Furthermore, in general, 1-acetyl imidazole can get ketones and aldehydes using Grignard reagent and reducing agent. Reaction of N, N-carbonyldimidazole and carboxyl will get useful reagent acyl imidazole. The relationship between imidazole and natural compounds is very close. For example, pyrimidine ring turns into purine derivatives after condensation. In addition to being like 6-amino purine and guanine the nucleic acid bases, it also exists in the organisms of uric acid, caffeine and theophylline. The catalytic action of imidazole, such as accelerated enzyme hydrolysis, still under study. As the cause of allergic skin, its toxicity is similar todiamine. Rat oral LD501880mg/kg. imidazole structure

Physical characteristics

In nature, there are only imidazole derivatives and no free imidazole. The precipitation from benzene is a colorless crystalline prism, with scents of ammonia. Relative molecular mass 68.08. Relative density 1.0303(101/4℃) . Melting point 89～91℃，boiling point 257℃，165℃～168℃(2.67×103Pa) and 138.2℃(1.60×103Pa). Flash point 145℃. Refractive index 1.4801(101℃). Viscosity 2.696mPa·s(100℃). Slightly soluble in benzene, petroleum ether, soluble in ether, acetone, chloroform and pyridine, easily soluble in water (at normal temperature 70) and ethanol. It appears weak alkaline. As the-NH-bond on 1 bite and-N= bond on 3 bit forms hydrogen bond, the boiling point is quite high; when 1 bit hydrogen is substituted, hydrogen bond cannot be formed, hence the boiling point decreases. As to thermal stability, it rarely dissolves under 250℃ (decomposition temperature is 590℃). It is also very stable to reducing agent and oxidant, but can form stable salt with inorganic acid. Owning some certain aromatic properties, also could get halogenation, nitration, sulfonation and hydroxymethylation in the presence of catalyst. Can be coupled with the heavy nitrogen salt in 2 bit. In addition, due to the =NH (1 bit) connected to the two double bonds, with some of the "acid", it can be replaced by metal to get salt. In addition, 3 bit nitrogen ions have coordination effect on metal ions, which can form chelate compounds. Although it is difficult to restore, but can be combined with the proton to generate cation type with resonance structure, and get of a stable form. Tautomers of imidazole ring are very easy to change, so it is hard to tell isomers on 4 bit or 5 bit. The above information is edited by the Chemicalbook He Liao Pu.

Chemical Properties

Imidazole is a moderately strong base (pKb= 7.0), and a weak acid (pKa= 14.9). Imidazoles substituted with electron-withdrawing groups are stronger acids than imidazole itself; e.g., 4(5)-nitroimidazole has a pKa of 9.3. Imidazole is stable at 400°C, possesses considerable aromatic character, and undergoes the usual electrophilic aromatic substitution reactions. Nitration and sulfonation require, however, far more drastic conditions than the corresponding reactions with benzene. Other substitution reactions of imidazole include halogenation, hydroxymethylation, coupling with aromatic diazonium salts, and carboxylation.

History

Imidazole[288-32-4] was first synthesized in 1858 by Debus from ammonia and glyoxal; it was originally named glyoxalin. The name imidazole was introduced by Hantzsch. Industrial production of imidazole began in the 1950s; a wide range of derivatives is now available in industrial quantities.

Uses

Imidazole is used as a buffer in the range of pH 6.2-7.8. It is also an histamine antagonist. It acts as a chelator and forms complexes with various divalent cations. It is used as a corrosion inhibitor on certain transition metals such as copper. Its derivatives, like polybenzimidazole (PBI), act as fire retardants. It finds application in photography and electronics. Imidazole salts are used as ionic liquids and precursors to stable carbenes. Imidazole derivatives like ketoconazole, miconazole and clotrimazole are involved in the treatment of various systemic fungal infections. It is a part of the theophylline molecule, present in tea leaves and coffee beans, which stimulates the central nervous system.

Application

Imidazole is a versatile heterocycle used in the preparation of various biologically active compounds such as the amino acid histidine and is present in many antifungal medication. It is also used ext ensively as a corrosion inhibitor on transition metals such as copper.It is used in organic synthesis and as an antiirradiationagent. Imidazole has been used:in the lysis, wash and elution buffer for the purification of histidine tagged Sonic Hedgehog(shh-N) protein.in elution buffer in stepwise gradient for the purification of histidine tagged aldo keto reductases using nickel affinity chromatography.as a component of homogenization buffer for the purification of phagosomal compartments from dendritic cell.

Preparation

Imidazole is formed by reacting glyoxal with formaldehyde in the presence of ammonium acetate in acetic acid. The driving energy is microwave radiation. More generally, this reaction is used to produce substituted imidazoles.Although there had been discoveries of various derivatives of imidazole in 1840, it was first reported in 1858. The synthesis process of imidazole follows the reaction between formaldehyde in ammonia and glyoxal. This process gives low yield of imidazole but it is still used to form imidazole with C-substitution (Wolkenberg et al., 2004).

Definition

ChEBI: Imidazole is an imidazole tautomer which has the migrating hydrogen at position 1. It is a conjugate base of an imidazolium cation. It is a conjugate acid of an imidazolide. It is a tautomer of a 4H-imidazole.

General Description

Imidazole is a heterocyclic compound with a five-membered planar ring. It is amphoteric and highly polar. The pharmacophore of imidazole exists in bioactive compounds including amino acids, plant growth regulators and therapeutic agents.

Health Hazard

It is less toxic relative to pyrrole and otherfive-membered heterocyclic compounds ofnitrogen. Intraperitoneal administration ofimidazole caused somnolence, muscle contractions,and convulsions in mice. Theoral LD50 value in mice is in the range900 mg/kg.

Fire Hazard

Noncombustible solid.

Flammability and Explosibility

Nonflammable

Biochem/physiol Actions

Imidazole derivatives have antibacterial, antifungal and anticancer functionality. It interacts with DNA and also binds to protein and stops cell division. It also acts as a microtubule destabilizing agents and inhibits topoisomerase and Cytochrome P450 Family 26 Subfamily A Member 1 (CYP26A1) enzymes. Imidazole based anticancer drug find applications in cancer chemotherapy. It is used as buffer component for purification of the histidine tagged recombinant proteins in immobilized metal-affinity chromatography (IMAC).

Purification Methods

Crystallise imidazole from *benzene, CCl4, CH2Cl2, EtOH, pet ether, acetone/pet ether and distilled de-ionized water. Dry it at 40o under vacuum over P2O5. Distil it at low pressure. It is also purified by sublimation or by zone melting. [Snyder et al. Org Synth Coll Vol III 471 1955, Bredereck et al. Chem Ber 97 827 1964, Caswell & Spiro J Am Chem Soc 108 6470 1986.] 15N-imidazole crystallises from *benzene [Scholes et al. J Am Chem Soc 108 1660 1986]. [Beilstein 23 II 34, 23 III/IV 564, 23/4 V 191.]

Consumer Uses

ECHA has no public registered data indicating whether or in which chemical products the substance might be used. ECHA has no public registered data on the routes by which this substance is most likely to be released to the environment.