Hydrazones and Azines

HydraZones and Azines. Depending on reaction conditions, hydrazines react with aldehydes and ketones to give hydrazones (33), azines (34), and diaziddines (35), the latter formerly known as isohydrazones. 

Many hydrazones and azines are colored and useful as dyestuffs. Examples are 2-hydroxynaphthazine, a yellow fluorescent dye (Lumogen LT Bright Yellow), and the pyridon—azino—quinone class of red-violet dyes. Numerous hydrazine derivatives are antioxidants and stabilizers by virtue of their reducing and chelating powers. 

Hydrazine is hypergolic with cone, nitric acid [1]. Of a series of hydrazones and azines derived from aldehydes and ketones, only those which decomposed when heated alone were hypergolic with the acid when heated at 12.5°C/min [2], Solid hydrazones formed from various aldehydes with dimethylhydrazine or phenylhydrazine are hypergolic with the acid [3],... 

Hydrazines are hydrogenolyzed catalytically over Raney nickel [741] and other catalysts. Hydrogenolysis of hydrazones and azines is discussed elsewhere (pp. 34, 106, 133, 134). 

The presence of a carbonyl substituent in the -position of the hetero-cycle is essential for the cleavage of five-membered rings. The compounds of this type which have been investigated most thoroughly are 3-acylindoles.287, 384-388 At 160-170° 3-acetylindole and hydrazine hydrate give 3-(o-aminophenyl)-5-methylpyrazole, the structure of which was proved by deamination. Other 3-acylindoles, their hydrazones, and azines, react analogously.385 For the mechanism of the reaction see Alberti.384,391 The reaction requires a fourfold excess of hydrazine hydrate,387 preferably a polar solvent,388 and about... 

Hydrogenation of hydrazones and azines is a useful way to prepare hydrazine derivatives. The hydrogenation may proceed further to amines depending on the structure of compound, catalyst, and reaction conditions. Unsubstituted hydrazones (I) are liable to hydrolysis, especially with the hydrazones derived from ketones in acidic media and slow hydrogenation. The ketones thus formed may afford azines (II) by condensation with the parent hydrazones. Hydrogenation of azines affords symmetrically... 

Dithiolium salts react with hydrazines similarly to amines, but further cyclization gives pyrazoles (46) or pyrazolium salts (47). When there are replaceable substituents, hydrazones and azines are formed. A mesoionic l,2-dithiole-3-olate (20 R = Ph) reacts similarly at C(3) with aniline, but with eventual formation of the products (48) and (49) <87CJC2830,92T8127). The reaction... 

ScHliMH 1. Formation of azines, hydrazones, and azine hydrazones. 

Hydrazones and azines can be reduced to A,iV -disubstituted hydrazines either catalytically or by metal hydride complexes.27d Sodium amalgam has also been applied successfully in a few cases to reduction of the C=N double bond of hydrazones.37,38 In general, hydrazones and azines of ketones are reduced more easily than their aldehyde analogs. 

Catalysts that are active for hydrogenation can be used equally for hydro-genolysis of an N-N bond Raney nickel is the catalyst of choice for this purpose 162 use of platinum or palladium catalysts generally leads only to the substituted hydrazine,144 145 N-N fission being rare in these cases.146 Experience to date does not permit prediction with certainty as to which compounds will suffer N-N fission on noble-metal catalysts it has been observed mainly with hydrazones and azines of aromatic aldehydes, but such catalysts have often been used in acid solution for reduction of hydrazones and azines to the corresponding hydrazines. 

Oximes, hydrazones and azines are obtainable from carbonyl com-poimds and can be reduced to primary amines (sometimes accompanied by secondary amines) in various ways (reaction 97)i62,i86 ... 

Table 7.30. J Coupling constants of hydrazines, hydrazones and azines...

Chemical Shifts and Coupling Constants of Imines, Oximes, Hydrazones, and Azines (5 in ppm relative to TMS)... 

Reaction with Aldehydes and Ketones. Classical preparations of aryl and alkyl hydrazones with hydrazine lead to mixtures of hydrazones and azines (eq 2). 

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