Azole

Azoles, colloquially pyrroles, are a group of heterocyclic chemical compounds. These are five-membered nitrogen- containing heteroaromatic ride whose parent compound is pyrrole. Through the formal hydrogenation of a double bond is obtained pyrrolines, the formal hydrogenation of both double bonds leads to the pyrrolidines.

Properties

Azole aromatic compounds. Five resonance structures can be formulated. Azoles satisfy the Hückel criteria by the participation of the lone pair of the nitrogen atom. With regard to their aromaticity they lie between the more aromatic thiophenes and the practically non- aromatic Oxolen.

Azoles have basic character by the free electron pair of the nitrogen atom.

At azoles Electrophilic aromatic substitution reactions can be carried out. Due to the better stabilization of the intermediates of this reaction, these take place in the 2-position is preferred. However, towards Lewis acids are not stable. These coordinate to the hetero atom and lead to ring opening.

Production

Azoles may be prepared by Paal -Knorr synthesis from dicarbonyls as diketones or dialdehydes and ammonia.

A further possibility is the synthesis Knorr pyrrole, are required to aldehydes and α -amino ketones.

Azole more heteroatoms

Pyrrole is not only the parent compound for the azoles, even more heterocyclic groups of substances derived from this structure. These include the imidazoles and pyrazoles, having two nitrogen atoms. With three nitrogen atoms of the triazoles and tetrazoles with fours are known. Among the azoles with various heteroatoms include oxazoles and thiazoles.

Imidazole

1,2,3- triazole

1,2,4-triazole

Tetrazole

Isoxazole

Oxazole

Isothiazole

Thiazole

Occurrence and use

Pyrroles are like most of heterocyclic compounds present in numerous natural products. These include for example the porphyrins, which form the basis of malice. Also available in other natural macrocyclic compounds such as Corrin they occur.

Azoles are present as fragments in a number of active ingredients. In plastics azoles occur for example in the polypyrrole.