Editing Hydrazine (section)

===Organic chemistry===
Hydrazines are part of many [[organic synthesis|organic syntheses]], often those of practical significance in [[pharmaceutical]]s (see applications section), as well as in textile [[dye]]s and in photography.<ref name=Ullmann/>

Hydrazine is used in the [[Wolff–Kishner reduction]], a reaction that transforms the [[carbonyl]] group of a [[ketone]] into a [[methylene bridge]] (or an [[aldehyde]] into a [[methyl group]]) via a [[hydrazone]] intermediate. Upon the catalysis with transition-metals, the hydrazones are used as organometallic reagent equivalents (HOME chemistry) for C-C bond formations.<ref>{{Cite journal |vauthors=Li, CJ |date=2023 |title=HOME chemistry: hydrazone as organo-metallic equivalent |journal=[[Pure Appl. Chem.]] |volume=95 |page=465-474 |doi=10.1515/pac-2022-1003|pmc=11585908 }}</ref> The production of the highly stable [[dinitrogen]] from the hydrazine derivative helps to drive the reaction.

Being bifunctional, with two amines, hydrazine is a key building block for the preparation of many heterocyclic compounds via condensation with a range of difunctional [[electrophiles]]. With [[2,4-pentanedione]], it condenses to give the [[3,5-Dimethylpyrazole|3,5-dimethylpyrazole]].<ref>{{Cite journal |vauthors=Wiley RH, Hexner PE |date=1951 |title=3,5-Dimethylpyrazole |journal=[[Organic Syntheses|Org. Synth.]] |volume=31 |page=43 |doi=10.15227/orgsyn.031.0043}}</ref> In the [[Einhorn-Brunner reaction]] hydrazines react with imides to give [[triazole]]s.

Being a good nucleophile, {{chem2|N2H4}} can attack sulfonyl halides and acyl halides.<ref>{{Cite journal |vauthors=Friedman L, Litle RL, Reichle WR |date=1960 |title=p-Toluenesulfonyl Hydrazide |journal=[[Organic Syntheses|Org. Synth.]] |volume=40 |page=93 |doi=10.15227/orgsyn.040.0093}}</ref> The [[tosyl]]hydrazine also forms hydrazones upon treatment with carbonyls.

Hydrazine is used to cleave ''N''-alkylated phthalimide derivatives. This scission reaction allows phthalimide anion to be used as amine precursor in the [[Gabriel synthesis]].<ref>{{Cite journal |vauthors=Weinshenker NM, Shen CM, Wong JY |date=1977 |title=Polymeric Carbodiimide. Preparation |journal=[[Organic Syntheses|Org. Synth.]] |volume=56 |page=95 |doi=10.15227/orgsyn.056.0095}}</ref>

====Hydrazone formation====
Illustrative of the condensation of hydrazine with a simple carbonyl is its reaction with acetone to give the [[acetone azine]]. The latter reacts further with hydrazine to yield [[acetone hydrazone]]:<ref>{{Cite journal |vauthors=Day AC, Whiting MC |date=1970 |title=Acetone Hydrazone |journal=Organic Syntheses |volume=50 |page=3 |doi=10.15227/orgsyn.050.0003}}</ref>

:{{chem2|2 (CH3)2CO + N2H4 → 2 H2O + ((CH3)2C\dN)2}}
:{{chem2|((CH3)2C\dN)2 + N2H4 → 2 (CH3)2C\dNNH2}}

The propanone azine is an intermediate in the Atofina-[[Pechiney–Ugine–Kuhlmann process|PCUK process]]. Direct [[alkylation]] of hydrazines with [[alkyl halides]] in the presence of base yields alkyl-substituted hydrazines, but the reaction is typically inefficient due to poor control on level of substitution (same as in ordinary [[amine]]s). The reduction of [[hydrazone]]s to hydrazines present a clean way to produce 1,1-dialkylated hydrazines.

In a related reaction, 2-cyanopyridines react with hydrazine to form amide hydrazides, which can be converted using [[diketone|1,2-diketones]] into [[triazine]]s.