Imidazole

Colorless crystals

Fixed

1.03 g · cm -3

90-91 ° C

257 ° C.

6.95 ( pKb, 25 ° C)

Soluble in water ( 633 g · l-1 at 20 ° C), ethanol, chloroform, diethyl ether and pyridine

1.4801 (101 ° C)

Risk

• 760 mg · kg -1 ( LD50, guinea pig, oral)
• 880 mg · kg -1 ( LD50, mouse, oral)
• 220 mg · kg -1 ( LD50, rat, oral)

49.8 kJ / mol

Template: Infobox chemical / molecular formula search available

Imidazole is a five-membered heterocyclic aromatic organic compound with two nitrogen atoms. It reacts as a base and is part of the side chain of the amino acid histidine.

Production and representation

Heinrich Debus introduced in 1858 for the first time here imidazole by reaction of glyoxal ( ethanedial ) with ammonia NH3, hence comes the name Glyoxalin outdated.

Today it can be represented by the Radziszewski synthesis by condensation of 1,2- diketone, an aldehyde and ammonia.

In recent times other way the synthesis of imidazoles and benzimidazoles, are described.

Properties and toxicology

Imidazole forms colorless crystals which dissolve readily in water. The heterocycle having both basic and acidic properties and is therefore an ampholyte. In warm-blooded acts of imidazole with LD50 values ​​between 220 ( rat) and 880 mg / kg body weight ( mouse) moderately toxic; in lower animals it has as an antimetabolite of histidine and of nicotinic acid a significantly higher toxicity and is therefore used as pesticides.

Use

Imidazole is mainly used as a starting material for the preparation of various medicines, in particular fungicides of Azoltyps, such as clotrimazole. Furthermore, it is used in the curing of certain plastics.

Also used to imidazole as a buffer when Karl Fischer method for water determination. Eugen Scholz developed in 1984, the pyridine-free Karl Fischer reagent with imidazole as the base. This reagent does not only replace the toxic and foul-smelling pyridine, it also allows a faster and more accurate titration, since imidazole buffers in a lower pH range than pyridine. The studies of the stoichiometry Scholz also showed that methanol ( solvent and at the same time involved in the reaction ) may be replaced by other alcohols such as ethanol, 2- propanol or methoxyethanol, would improve the titer stability of the reagent. Based on these findings, the following equation for the Karl Fischer reaction was:

In biochemistry, imidazole is used for elution of proteins with a Histidine -tag ( a plurality of consecutive histidines ) are provided. The proteins are bound to a metal ion chelate matrix (IMAC ), such as Ni 2 -NTA and washed by high concentrations of imidazole again from the column.