Azine

Not to be confused with azene.

This article is about the hydrazine derivatives. For the use of "azine" in the names of heterocyclic compounds, see Azine (heterocycle).

Azines are a functional class of organic compounds with the connectivity RR′C=N−N=CRR′. These compounds are the product of the condensation of hydrazine with ketones and aldehydes, although in practice they are often made by alternative routes. Ketazines are azines derived from ketones.^[1] For example, acetone azine is the simplest ketazine. Aldazines are azines derived from aldehydes.^[2]

The generic formula of an azine. For an aldazine, R² = H.

Preparation

The usual method of industrial production is the peroxide process, starting from the ketone, ammonia, and hydrogen peroxide.^[3]

In the laboratory, azines are typically prepared by condensation of hydrazine with two equivalents of a carbonyl.^[4]

Azines are also produced when chalcone reacts with a hydrazone to produce 3,5-diphenyl-1H-pyrazole,^[5] in a conversion also carried out with hydrazine hydrate.^[6][7]

Reactions

Azines characteristically undergo hydrolysis to hydrazines. The reaction proceeds by the intermediacy of a hydrazone:

R₂C=N−N=CR₂ + H₂O → R₂C=N−NH₂ + R₂C=O

R₂C=N−NH₂ + H₂O → N₂H₄ + R₂C=O

Azines have been used as precursors to hydrazones:^[4][8]

R₂C=N−N=CR₂ + N₂H₄ → 2R₂C=N−NH₂

They are also precursors to diazo compounds.^[9][8][10]

The coordination chemistry of azines (as ligands) has also been studied.^[11][12][13]

Acetone is used to derivatize hydrazine into acetone azine for analysis by gas chromatography. This method is used to determine trace levels of hydrazine in drinking water^[14] and pharmaceuticals.^[15]

Applications

Ketazines are also important intermediates in the industrial production of hydrazine hydrate by the peroxide process.^[3] In the presence of an oxidant, ammonia and ketones react to give hydrazine via ketazine:

2 Me(Et)C=O + 2 NH₃ + H₂O₂ → Me(Et)C=NN=C(Et)Me + 2 H₂O

The ketazine can be hydrolyzed to the hydrazine and regenerate the ketone:

Me(Et)C=NN=C(Et)Me + 2 H₂O → 2 Me(Et)C=O + N₂H₄

Ketazines have been also used as sources of hydrazine produced in situ, for example in the production of herbicide precursor 1,2,4-triazole.^[16]