Hydrazones from azines

Hydrazones are formed from mono- and Ai,A/-disubstituted hydrazines. Hydrazine itself can give either hydrazones or azines, depending mainly on the ratio of carbonyl component to hydrazine. The ease of formation of these compounds depends on the nature of the carbonyl constituent ... 

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],... 

Other imino derivatives arise, as by-products or in side reactions, on heterocyclization. Thus, the treatment of cinnamoyltropolones 75 with hy-droxylamine (Scheme 19) yields, in the case of the 5-nitro derivative, the corresponding isoxazolotroponeoxime (89JHC371). The formation of oximes and several hydrazones from 3-acetyltropolone or its derivatives has also been mentioned (Section II,A,3,c). Moreover, an azine was obtained in addition to quinoxalotropone 213 (Section II,B,2,c) a tropone immonium salt was isolated after an extremely complex diene reaction of an 6-amino-2-azaazuIene (93CB441). 

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... 

Pyridazines were prepared from a variety of hydrazones or azines. 

Hydrazones. A useful procedure for preparation of hydrazones free from azines is exemplified by the preparation of acetone hydrazone.1 Acetone is first converted into acetone azine (b.p. 128-131°) by reaction with 100% hydrazine hydrate and potassium hydroxide this product is then converted into acetone hydrazone by reaction with anhydrous hydrazine2 and sodium hydroxide. 

Pyridazines were prepared from a variety of hydrazones or azines. 3,6-Di- or 3,4,6-triphenylpyridazine were prepared from acetophenone hydrazone and deoxybenzoin [Eq. (2)]. The azine was first converted into... 

Heptanal bydrazone mixed with dipbenylketimine beptanal benzopbenone azine. Y ca. 100%. F. e. s. J. Guenzet, Bl. 1961, 1012 similarly hydrazones from hydrazines and imines s. Bl. 1960, 1549. 

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 ... 

Azines, Aldehydes react with hydrazine to yield azines the reaction cannot usually be arrested at the hydrazone stage. This reaction may be illustrated by the preparation of bevzalazine from benzaldehyde ... 

This silyl hydrazone formation-oxidation sequence was originally developed as a practical alternative to the synthesis and oxidation of unsubstituted hydrazones by Myers and Furrow [31]. The formation of hydrazones directly from hydrazine and ketones is invariably complicated by azine formation. In contrast, silyl hydrazones can be formed cleanly from /V,/V -bis(7< rt-butyldimethylsilyl)hydrazine and aldehydes and ketones with nearly complete exclusion of azine formation. The resulting silylhydrazones undergo many of the reactions of conventional hydrazones (Wolff-Kishner reduction, oxidation to diazo intermediate, formation of geminal and vinyl iodides) with equal or greater efficiency. It is also noteworthy that application of hydrazine in this setting may also have led to cleavage of the acetate substituents. 

Alkyl-3-formylcarbazoles form-arylhydrazones " and azines or hydrazones with hydrazine. 9-Ethyl-3-formylcarbazole gives Schiflf bases with arylamines. Variously substituted 3-formylcarbazoles condense with aminoacetal, " and the resulting imines are easily reduced catalytically or with sodium borohydride. Anils from... 

Ethylenimines or aziridines [lb] can be considered cyclic imines and are only briefly covered in Section 5. The preparation of heterocyclic imine systems, semicarbazones, hydrazones, azines, and oximes, is omitted from this chapter. The synthesis of carbodiimides is presented in Chapter 9. 

Although the last method gives satisfactory results, it requires a large excess of iodine monofluoride which has to be prepared from iodine and fluorine just prior to use. Furthermore, most of the unsubstituted hydrazones are rather unstable and undergo transformation into azines which are unrcactive towards iodine monofluoride. O-Methyloximes are also inactive with respect to iodine monofluoride. The procedure with bromine trifluoride is free of such limitations. 

Starting from isolated hydrazones, reduction to the corresponding hydrocarbons by treatment with base in an aprotic solvent takes place at temperatures significantly below the 200 °C of the Huang-Minlon modification of the Wolff-Kishner reduction. However, hydra-zones cannot be prepared in a one-step reaction between a ketone and hydrazine, since usually azines (R1R2C=N=N=CR1R2) are formed instead. However, semicarbazones are hydrazone derivatives that are easily accessible by the reaction of a ketone with semicarbazide (for the mechanism, see Table 9.2). Semicarbazones can be converted into alkanes with KO/Bu in toluene at temperatures as low as 100 °C. This method provides an alternative to the Wolff-Kishner reduction when much lower than usual reduction temperatures are desirable. 

Starting from previously isolated hydrazones, it turns out that they can be reduced to the corresponding hydrocarbons by treatment with base in an aprotic solvent at temperatures significantly below the 200°C of the Huang-Minlon modification of the Wolff-Kishner reduction. However, hydrazones cannot be prepared in a one-step reaction between a ketone and hydrazine, since usually azines... 

A stereoselective synthesis of 3-( 1,2,4-triazolo[4,3-A ]azin-3-yl)-bicyclo[2.2.1 ]heptanones 58 starting from (l/ )-(+)camphor 56 has been described. The reaction comprises oxidative cyclization of the intermediate hydrazones 57 with methanolic bromine <02TA821>. 

A convenient synthesis [Eq. (13)] of 2-ary lidenehydrazono-4-thia-zolidinone (43) from ethyl thiocyanoacetate (44), arylideneazines (45), and hydrazine hydrate (46) has been reported.79 Presumably, the reaction proceeds via the intermediary hydrazone, which condenses with 44 to give 43. Subsequently, condensation of 43 with the aromatic aldehyde, generated in situ from disproportionation of the azine with hydrazine, affords the 5-arylidene derivative. The reaction of 44 with ammonium acetate and an aromatic aldehyde gives 5-arylidene-2-imino-4-thiazolidinones.80... 

The procedure for acetone azine is essentially that of Curtius and Thun.5 The method for acetone hydrazone is adapted from that of Staudinger and Gaule.8 The hydrazone has been prepared directly from acetone and hydrazine, but this is much less satisfactory.6... 

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