Hydrazone

Hydrazones as is known in the chemistry of the hydrazine or derivatives ( phenylhydrazine, 2,4- dinitrophenylhydrazine, etc.) formed imine analogous substances that are formed by condensation with aldehydes or ketones. R1 and R2 may be different or the same organic radicals and hydrogen atoms. The formation of the hydrazones proceeds according to the following scheme:

The reaction of two equivalents of the carbonyl compound with hydrazine to form the first hydrazone then forming an azine occurs.

Analytical meaning

Special analytical meanings 2,4- dinitrophenylhydrazones enabling as well crystallizing carbonyl identifying carbonyl compounds ( in particular aldehydes and ketones ) over the melting point of the 2,4- dinitrophenylhydrazone.

History

Of historical importance are the phenyl hydrazones of sugars, which is also referred to as osazones. When working on the diazotization of aniline the phenylhydrazine was discovered in 1874 by Emil Fischer, it was later used for the characterization of sugars. Aldoses and ketoses, the keto group is located at C- 2 form with three equivalents of phenylhydrazine twofold hydrazones on - and atom. The formation of the osazones is connected to a redox reaction; one mole of phenylhydrazine is reduced to aniline, and ammonia, a hydroxyl group of the monosaccharide is oxidized to a carbonyl group.

Properties

With a suitable substitution pattern subject hydrazones of the azo - hydrazone tautomerism.

Syntheses

Preparative meanings hydrazones in Wolff -Kishner reaction. Columns upon deprotonation from nitrogen, thus allowing the selective reduction of ketones and aldehydes to alkanes.