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Hydrazine should not be confused with Hydergine (Ergoloid mesylates) an alkoloid

Hydrazine
General
Systematic name	Hydrazine
Other names
Molecular formula	N2H4
Molar mass	32.05 g/mol
Appearance	Colourless liquid
CAS number	[302-01-2]
Properties
Density and phase	1.01 g/mL (liquid)
Solubility in water	infinitely miscible
Other solvents	miscible with polar organic solvents
Melting point	274 K (1 °C)
Boiling point	387 K (114 °C)
Viscosity	0.9 cP at 25°C
Thermochemistry
ΔfH0gas	95.35 kJ/mol
ΔfH0liquid	50.63 kJ/mol
ΔfH0solid	37.63 kJ/mol
S0gas, 1 bar	238.66 J/mol·K
S0liquid, 1 bar	121.52 J/mol·K
S0solid	? J/mol·K
Structure
Molecular shape	pyramidal at N
Dipole moment	1.85 D
Hazards
MSDS	External MSDS
Main hazards	Toxic, causes burns
LD50	25mg/kg
NFPA 704	3 3 3
Flash point	37.78°C (closed cup)
R/S statement	R: 45-10-23/24/25-34-43-50/53 S: 53-45-60-61
RTECS number	MU7175000
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Refractive index	n20/D 1.47
Related compounds
Related hydrides	hydrogen peroxide
Related compounds	ammonia monomethylhydrazine dimethylhydrazine phenylhydrazine
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Hydrazine is the chemical compound with formula N₂H₄, widely used in chemical synthesis. It is notable as a component in rocket fuel. Hydrazine is also found in tobacco products. It has an ammonia-like odor.

Contents 1 Molecular structure and properties 2 Synthesis 3 Hydrazine derivatives 4 Uses in chemistry 4.1 Hydrazone formation 4.2 Wolff-Kishner reduction 4.3 Heterocyclic chemistry 4.4 Sulfonation 4.5 Deprotection of phthalimides 4.6 Reducing agent 4.7 Hydrazinium salts 5 Other industrial uses 5.1 Rocket fuel 6 Safety 7 References 8 See also 9 External links

Conceptually, hydrazine arises via coupling a pair of ammonia molecules by removal of one H per molecule. Each H₂N-N subunit is pyramidal. The N-N distance is 1.45 Å, and the molecule adopts a gauche conformation^[1]. The rotational barrier is twice that of ethane. These structural properties resemble that of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier.

Hydrazine has a liquid range and density like water's. It has basic properties comparable to ammonia but 15-times weaker. It can be deprotonated only with difficulty:^[2]

N₂H₄ + H⁺ → [N₂H₅]⁺ K = 8.5 x 10^-7

(for ammonia K = 1.78 x 10^-5)

[N₂H₅]⁺ + H⁺ → [N₂H₆]²⁺ K = 8.4 x 10^-16

Theodor Curtius synthesized free hydrazine for the first time in 1889 via a circuitous route.^[3]

Hydrazine is produced in the Olin Raschig process from sodium hypochlorite and ammonia, a process developed in 1907. This method relies on the reaction of chloramine with ammonia.^[4]

In the Atofina-PHUK cycle, hydrazine is produced in several steps from acetone, ammonia, and hydrogen peroxide. Acetone and ammonia first react to give the imine followed by oxidation with hydrogen peroxide to the oxaziridine, a three-membered ring containing carbon, oxygen, and nitrogen, followed by ammonolysis to the hydrazone, a process that couples two nitrogen atoms. This hydrazone reacts with one more equivalent of acetone, and the resulting azine is hydrolyzed to give hydrazine, regenerating acetone. Unlike the Raschig process, this process does not produce salt.

Hydrazine can also be produced via the ketazine and the peroxide processes.

Many substituted hydrazines are known, and several occur naturally. Some examples:

• gyromitrin and agaritine are phenylhydrazines found in the commercially produced mushroom species Agaricus bisporus. Gyromitrin is metabolized into monomethyl hydrazine.
• iproniazid, hydralazine and phenelzine are hydrazine-containing medications.
• 1,1-dimethylhydrazine and 1,2-dimethylhydrazine are hydrazines where two hydrogen atoms are replaced by methyl groups.
• 2,4-dinitrophenylhydrazine (2,4-DNP) is commonly used to test for ketones and aldehydes in organic chemistry.
• phenylhydrazine, C₆H₅NHNH₂, the first hydrazine to be discovered.

Hydrazines are part of many organic syntheses, often those of practical significance in pharmaceuticals, such as antituberculants, as well as in textile dyes and photography.

Illustrative of the condensation of hydrazine with a simple carbonyl is its reaction with acetone to give the azine. This azine reacts further with hydrazine to afford the hydrazone:^[5]

2 (CH₃)₂CO + N₂H₄ → 2 H₂O + [(CH₃)₂C=N]₂

[(CH₃)₂C=N]₂ + N₂H₄ → 2 (CH₃)₂C=NNH₂

The acetone azine is an intermediate in the Atofina-PCUK synthesis. Direct alkylation of hydrazines with alkyl halides in the presence of base affords alkyl-substituted hydrazines, but the reaction is typically inefficient due to poor control on level of substitution (same as in ordinary amines). The reduction of hydrazones to hydrazines present a clean way to produce 1,1-dialkylated hydrazines.

In a releated reaction 2-cyanopyridines react with hydrazine to form amide hydrazides which can be converted using 1,2-diketones into triazines.

Hydrazine is used in the Wolff-Kishner reduction, a reaction that transforms the carbonyl group of a ketone or aldehyde into a methylene (or methyl) group via a hydrazone intermediate. 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 dimethylpyrazole.^[6] In the Einhorn-Brunner reaction hydrazines react with amides to give triazoles.

Being a good nucleophile, N₂H₄ is susceptible to attack by sulfonyl halides and acyl halides.^[7] The tosylhydrazine 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.^[8]

Hydrazine is a convenient reductant because the by-products are typically nitrogen gas and water. Thus, it is used as an antioxidant, an oxygen scavenger, and a corrosion inhibitor in water boilers and heating systems. It is also used to reduce metal salts and oxides to the pure metals in electroless nickel plating and plutonium extraction from nuclear reactor waste.

Hydrazine is converted to solid salts by treatment with mineral acids. A common salt is hydrazine hydrogen sulfate, [N₂H₅]HSO₄, which probably should be called hydrazinium sulfate. The salt of hydrazine and hydrazoic acid N₅H₅ were of scientific interest, because of the high nitrogen content and the explosive properties.

Hydrazine is used in many processes including: production of spandex fibers, as a polymerization catalyst, a blowing agent, in fuel cells, solder, fluxes, and photographic developers, as a chain extender in urethane polymerizations, and heat stabilizers. In addition, a semiconductor deposition technique using hydrazine has recently been demonstrated, with possible application to the manufacture of thin-film transistors used in liquid crystal displays. Hydrazine in a 70% hydrazine, 30% water solution is used to power the EPU (emergency power unit) on the F-16 fighter plane. The explosive Astrolite is made by combining hydrazine with ammonium nitrate.

Hydrazine is also used as rocket fuel starting in World War II for the Messerschmitt Me 163, under name B-Stoff (hydrazine hydrate) and in a mixture with methanol (M-Stoff) and hydrogen peroxide called C-Stoff.

Hydrazine is also used as a low-power monopropellant for the maneuvering thrusters of spacecraft, and the Space Shuttle's Auxiliary Power Units. In addition, monopropellant hydrazine-fueled rocket engines are often used in terminal descent of spacecraft. A collection of such engines were used in both Viking landers as well as the Phoenix lander scheduled to launch in August 2007.

In all hydrazine monopropellant engines the hydrazine is passed by a catalyst such as iridium metal supported by high-surface-area alumina (aluminium oxide) or carbon nanofibers,^[9] or more recently molybdenum nitride on alumina,^[10] which causes it to decompose into ammonia, nitrogen gas, and hydrogen gas according to the following reactions:

1. 3 N₂H₄ → 4 NH₃ + N₂
2. N₂H₄ → N₂ + 2 H₂
3. 4 NH₃ + N₂H₄ → 3 N₂ + 8 H₂

These reactions are extremely exothermic (the catalyst chamber can reach 800 °C in a matter of milliseconds^[9]), and they produce large volumes of hot gas from a small volume of liquid hydrazine,^[10] making it an efficient thruster propellant.

Hydrazine is highly toxic and dangerously unstable, especially in the anhydrous form. Symptoms of acute (short-term) exposure to high levels of hydrazine may include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, and coma in humans. Acute exposure can also damage the liver, kidneys, and central nervous system in humans. The liquid is corrosive and may produce dermatitis from skin contact in humans and animals. Effects to the lungs, liver, spleen, and thyroid have been reported in animals chronically (long-term) exposed to hydrazine via inhalation. Increased incidences of lung, nasal cavity, and liver tumors have been observed in rodents exposed to hydrazine.

• List of Stoffs
• Links to external chemical sources

• The Late Show with Rob! Tonight’s Special Guest: Hydrazine (PDF) — Robert Matunas
• xMSDS-Hydrazine-9924279 (PDF) — MSDS for hydrazine