Excess hydrazine

This reaction forms the basis of one method of terminal residue analysis A peptide is treated with excess hydrazine in order to cleave all the peptide linkages One of the terminal amino acids is cleaved as the free amino acid and identified all the other ammo acid residues are converted to acyl hydrazides Which amino acid is identified by hydrazmolysis the N terminus or the C terminus ... 

Treatment of a hydtoxyirninoirnine with one equivalent of hydrazine hydrate gave a nitrosopyrazole, which on addition of excess hydrazine hydrate yielded a 4-aminopytazole derivative (eq. 6) (37). 

A nonbasic enamine is formed from decafluorocyclohexene and pyrrolidine L9J], whereas condensation of perfluorocyclobutene with excess hydrazine produces the tetrakishydrazone of cyclobutanetetrone [94] (equation 80). 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C—has been replaced almost completely by the modified procedure after Huang-Minlon The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tcrt-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

The reaction mixture is then warmed on the steam bath for an additional two hours (90°C to 95°C). The excess hydrazine hydrate is removed in vacuo. The residue of viscous 1-hy-drazlno-3-morpholinyl-2-propanol Is not distilled, but is mixed with 10.16 g (0.0B6 mol) diethyl carbonate and a solution of 0.3 g sodium metal in 15 ml methyl alcohol. The mixture is refluxed about 2 hours under a 15 cm Widmer column, the alcohol being removed leaving a thick, green liquid residue, which is cooled and the precipitate which forms is removed by filtration and washed well with ether. Yield B2%, MP114°C to 116°C. Recrystallization from isopropanol gives purified 3-amino-5-(N-morpholinyl)-methyl-2-oxazolidone, MP 120°C as the intermediate. 

Chemical reducing conditions and flow geometries are optimized to minimize EC. Reducing conditions especially must not be too severe (as may happen with excess hydrazine) to prevent autocat-alytic EC mechanisms proliferating. 

However, in some cases azines can be converted to hydrazones by treatment with excess hydrazine and NaOH. Arylhydrazines, especially phenyl, p-nitrophenyl, and 2,4-dinitrophenyl, are used much more often and give the corresponding hydrazones with most aldehydes and ketones.Since these are usually solids, they make excellent derivatives and are commonly employed for this purpose. Cyclic hydrazones are also known, ° as are conjugated hydrazones. a-Hydroxy aldehydes and ketones and ot-dicarbonyl compounds give osazones, in which two adjacent carbons have carbon-nitrogen double bonds ... 

Rondevstedt, C. S., Chem. Eng. News, 1977, 55(27), 38 Synthesis, 1977, 851-852 In an attempt to reduce 2-chloro-5-methylnitrobenzene to the aniline by treatment with excess hydrazine and Pd/C catalyst, the hydroxylamine was unexpectedly produced as major product. During isolation of the product, after removal of solvent it was heated to 120°C under vacuum and exploded fairly violently. Many aryl-hydroxylamines decompose violently when heated above 90-100°C, especially in presence of acids. GLC is not suitable as an analytical diagnostic for arylhydroxyl-amines because of this thermal decomposition. 

To corroborate the proposed mechanism, the catalytic reductive aldol coupling of acrolein with phenyl glyoxal monohydrate was performed under 1 atmos. elemental deuterium. Exposure of the aldol product to excess hydrazine in situ results in formation of the pyridazine, which incorporates precisely one deuterium atom in a manner consistent with the general mechanism proposed in Scheme 22.4 (Scheme 22.9). 

The acyl-azide method of coupling (Figure 2.13) has been available for about a century, but it is not attractive for routine use because it involves four distinct steps that include two stable intermediates that require purification. In addition, aminolysis of the azide is slow. The first step involves preparation of the ester (see Section 3.17), which can be methyl, ethyl, or benzyl. The ester is converted to the hydrazide by reaction in alcohol with excess hydrazine at ambient or higher... 

Chantegral, Hartmann, and Gelin (77T45) reported synthesizing 21 from the reaction of 18a with excess hydrazine. The intermediate pyrazole derivative 19 was isolated. The reaction of 18b with hydrazine directly afforded 20 (Scheme 3). 

Opening of the ring and expulsion of thiobenzamide and sulfur leads to the thiadiazole (180). The preferential attack of (177) on (178) instead of the excess hydrazine present in the reaction mixture is partially explained by differences in solubilities <88BCJ4043>. 

Table 26 Reaction of 2-chloro-3-cyanopyridine 136 with excess hydrazines (Equation 48) <2004TL2389>...

The pyrimidine 371 reacts with hydrazine hydrate in refluxing ethanol to yield 372. This cyclized to 373 on reflux in -butanol. Compound 374 was formed directly upon treatment of 371 with excess hydrazine hydrate (Scheme 32) <2000JHC707>. 

In the first stage of the reaction an alkoxyl anion and the nitrohydrazine cation are formed which afterwards react together to give the corresponding alcohol and nitrohydrazine. Nitrohydrazine reacts with excess hydrazine to produce tetrazene, nitrous acid and di-imid. Then the tetrazene decomposes to form ammonia and nitrogen from di-imid on the other hand tetrazene, hydrazine and nitrogen are formed. Hydrazoic acid and ammonia are then formed as decomposition products of tetrazene. 

A number of symmetrically 3,5-disubstituted 4-amino-1,2,4-triazoles were able to be rapidly synthesised via focussed microwave heating, by the reaction of aromatic nitriles with excess hydrazine hydrate in ethylene glycol, in the presence of hydrazine dihydrochloride (Scheme 3.21)37. 

Aldehyde (166) reacted with excess hydrazine hydrochloride to afford a pyrazoline in 63% yield a mixture of pyrazoline and pyrazolidine was obtained under an inert atmosphere.83 This reaction presumably involves the hydrazone and protonated azomethine imine as intermediates. Using (166) in excess afforded a bisintramolecular adduct in 87% yield. 

Reaction of alkynyl-substituted anthraquinones 57 with excess hydrazine in pyridine at 90-115 °C for 20-90 min gave mixtures of diazepineanthrones 58 (45-64%) and pyridineanthrones 59 (17-38%) <2001MI582> (Scheme 12). 

The reaction of l,6-bis[2-bromotellurophenyl]-2,5-diaza-l,5-hexadiene with an excess of hydrazine hydrate in refluxing ethanol produced the ditelluride via hydrolysis of the Schiff base to the aldehyde that combined with excess hydrazine to form the hydrazone3. 

Pyrazoles and isoxazoles from 1,3-diketones. The standard syntheses for pyrazoles 41 and isoxazoles 43 involve the reactions of -dicarbonyl compounds 42 with hydrazines and hydroxylamine, respectively (Scheme 31). These reactions take place under mild conditions and are of very wide applicability the substituents R can be H, alkyl, aryl, GN, G02Et, etc. For example, 4-alkoxypyrazoles 45 can be prepared from diketones 44 and hydrazine (Scheme 32) <2002SL1170>, while diketooximes 46 react with excess hydrazine in ethanol to give 4-amino-3,5-disubstituted pyrazoles 47 in generally good yields (Scheme 33) <2004TL2137>. 

In excess hydrazine, the reaction in Eq. 3 occurs, producing hydrazoic acid, HN3. In excess HN02, the reaction in Eq. 4 occurs. Hydrazoic acid is known to react vigorously with HN02 and has been suggested as an intermediate in Eq. 5 [71] ... 

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