|Jmol-3D images||Image 1|
|Molar mass||32.0452 g mol−1|
|Density||1.021 g cm−3|
|Melting point||2 °C; 35 °F; 275 K|
|Boiling point||114 °C; 237 °F; 387 K|
|Vapor pressure||1 kP (at 30.7 °C)|
|Refractive index (nD)||1.46044 (at 22 °C)|
|Molecular shape||Triangular pyramidal at N|
|Dipole moment||1.85 D|
|121.52 J K−1 mol−1|
|Std enthalpy of
|50.63 kJ mol−1|
|GHS signal word||DANGER|
|GHS hazard statements||H226, H301, H311, H314, H317, H331, H350, H410|
|GHS precautionary statements||P201, P261, P273, P280, P301+310, P305+351+338|
|EU classification||T+ N |
|R-phrases||R45, R10, R23/24/25, R34, R43, R50/53|
|S-phrases||S53, S45, S60, S61|
|Flash point||52 °C (126 °F; 325 K)|
|Autoignition temperature||24 to 270 °C (75 to 518 °F; 297 to 543 K)|
|LD50||59–60 mg/kg (oral in rats, mice)|
|Other cations||organic hydrazines|
|Related Binary azanes||Ammonia
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Hydrazine (also called diazane) is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. As of 2000[update], approximately 120,000 tons of hydrazine hydrate (corresponding to a 64% solution of hydrazine in water by weight) were manufactured worldwide per year. Hydrazine is mainly used as a foaming agent in preparing polymer foams, but significant applications also include its uses as a precursor to polymerization catalysts and pharmaceuticals. Additionally, hydrazine is used in various rocket fuels and to prepare the gas precursors used in air bags. Hydrazine is used within both nuclear and conventional electrical power plant steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen in an effort to reduce corrosion.
- 1 Molecular structure and properties
- 2 Synthesis and manufacture
- 3 Applications
- 4 Hydrazine in biology
- 5 Organic chemistry
- 6 Other industrial uses
- 7 Hazards
- 8 History
- 9 See also
- 10 References
- 11 External links
Molecular structure and properties
Hydrazine can arise via coupling a pair of ammonia molecules by removal of one hydrogen per molecule. Each H2N-N subunit is pyramidal in shape. The N-N single bond distance is 1.45 Å (145 pm), and the molecule adopts a gauche conformation. The rotational barrier is twice that of ethane. These structural properties resemble those of gaseous hydrogen peroxide, which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier.
- N2H4 + H2O → [N2H5]+ + OH−
with the values:
- Kb = 1.3 x 10−6
- pKa = 8.1
(for ammonia Kb = 1.78 x 10−5)
Hydrazine is difficult to diprotonate:
- [N2H5]+ + H2O → [N2H6]2+ + OH− Kb = 8.4 x 10−16
The heat of combustion of hydrazine in oxygen (air) is 1.941 x 107 J/kg (9345 BTU/lb).
Synthesis and manufacture
Different routes have been developed over the years, with the key step being the creation of the nitrogen-nitrogen single bond.
Oxidation by chloroamine from hypochlorite on ammonia
Hydrazine is produced in the Olin Raschig process from sodium hypochlorite (the active ingredient in many bleaches) and ammonia, a process announced in 1907. This method relies on the reaction of chloramine with ammonia to create the nitrogen-nitrogen single bond:
- NH2Cl + NH3 → H2N-NH2 + HCl
Oxidation by oxaziridine from peroxide on ammonia
Hydrazine can be synthesized from ammonia and hydrogen peroxide in the Peroxide process (sometimes called Pechiney-Ugine-Kuhlmann process, the Atofina–PCUK cycle, or ketazine process). The net conversion follows:
- 2 NH3 + H2O2 → H2N-NH2 + 2 H2O
In these routes, hydrazine is produced in several steps from acetone or methylethyl ketone, ammonia, and hydrogen peroxide. The ketone and ammonia first condense to give the imine, which is oxidised by hydrogen peroxide to the oxaziridine, a three-membered ring containing carbon, oxygen, and nitrogen. Next, the oxaziridine gives hydrazone by ammonolysis, a process creating the nitrogen-nitrogen single bond. This hydrazone reacts with one more equivalent of ketone; the resulting acetone azine is hydrolyzed to give hydrazine and regenerate acetone. Unlike the Raschig process, this approach process does not produce a salt.
Oxidation from hypochlorite on urea
- (H2N)2C=O + NaOCl + 2 NaOH → N2H4 + H2O + NaCl + Na2CO3
The majority use of hydrazine is as a precursor to blowing agents. Specific compounds include azodicarbonamide and azobisisobutyronitrile, which yield 100-200 mL of gas per gram of precursor. In a related application, sodium azide, the gas-forming agent in air bags, is produced from hydrazine by reaction with sodium nitrite.
Hydrazine is also used as a propellant on board space vehicles, and to both reduce the concentration of dissolved oxygen in and control pH of water used in large industrial boilers. The F-16 fighter jet uses hydrazine to fuel the aircraft's emergency power unit.
Precursor to pesticides and pharmaceuticals
Hydrazine is a useful building block in organic synthesis of pharmaceuticals and pesticides. One example is 3-amino-1,2,4-triazole and another is maleic hydrazide. The antitubercular drug isoniazid is prepared from hydrazine.
Hydrazine in biology
Hydrazine is the intermediate in the anaerobic oxidation of ammonia (anammox) process. It is produced by some yeasts and the open ocean bacterium anammox (Brocadia anammoxidans). The false morel produces the poison gyromitrin which is an organic derivative of hydrazine that is converted to monomethylhydrazine by metabolic processes. Even the most popular edible "button" mushroom Agaricus bisporus produces organic hydrazine derivatives, including agaritine, a hydrazine derivative of an amino acid, and gyromitrin.
Hydrazines are part of many organic syntheses, often those of practical significance in pharmaceuticals, such as the antituberculosis medication isoniazid and the antifungal fluconazole, as well as in textile dyes and in photography.
Illustrative of the condensation of hydrazine with a simple carbonyl is its reaction with propanone to give the diisopropylidene hydrazine (acetone azine). The latter reacts further with hydrazine to yield the hydrazone:
- 2 (CH3)2CO + N2H4 → 2 H2O + [(CH3)2C=N]2
- [(CH3)2C=N]2 + N2H4 → 2 (CH3)2C=NNH2
The propanone azine is an intermediate in the Atofina-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 amines). The reduction of hydrazones to hydrazines present a clean way to produce 1,1-dialkylated hydrazines.
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. 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. In the Einhorn-Brunner reaction hydrazines react with imides to give triazoles.
Deprotection of phthalimides
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. Some colour photographic processes also use a weak solution of hydrazine as a stabilizing wash, as it scavenges dye coupler and unreacted silver halides. Hydrazine is the most common and effective reducing agent used to convert graphene oxide (GO) to reduced graphene oxide (rGO) via hydrothermal treatment.
Hydrazine is converted to solid salts by treatment with mineral acids. A common salt is hydrazine sulfate, [N2H5]HSO4, called hydrazinium sulfate. Hydrazine sulfate was investigated as a treatment of cancer-induced cachexia, but proved ineffective.
Hydrazine azide (N5H5), the salt of hydrazine and hydrazoic acid, was of scientific interest, because of its high nitrogen content and explosive properties. Structurally, it is [N
. It decomposes explosively into hydrazine, ammonia and nitrogen gas:
- 12 N
5 → 3 N
4 + 16 NH
3 + 19 N
Reaction of N
5 with sulfuric acid gives quantitative yields of pure hydrazine sulfate and hydrazoic acid.
Other industrial uses
Hydrazine is used in many processes including: production of spandex fibers, as a polymerization catalyst; 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 Lockheed F-16 Fighting Falcon fighter plane. The explosive Astrolite is made by combining hydrazine with ammonium nitrate.
Hydrazine is often used as an oxygen scavenger and corrosion inhibitor in boiler water treatment. However due to the toxicity and certain undesired effects[clarification needed] this practice is discouraged.
Hydrazine was first used as a rocket fuel during World War II for the Messerschmitt Me 163B (the first rocket-powered fighter plane), under the code name B-Stoff (hydrazine hydrate). When mixed with methanol (M-Stoff) and water it was 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 (APUs). In addition, monopropellant hydrazine-fueled rocket engines are often used in terminal descent of spacecraft. Such engines were used on the Viking program landers in the 1970s as well as the Phoenix lander and Curiosity rover which landed on Mars in May 2008 and August 2012, respectively.
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, or more recently molybdenum nitride on alumina, which causes it to decompose into ammonia, nitrogen gas, and hydrogen gas according to the following reactions:
- 3 N2H4 → 4 NH3 + N2
- N2H4 → N2 + 2 H2
- 4 NH3 + N2H4 → 3 N2 + 8 H2
Reactions 1 and 2 are extremely exothermic (the catalyst chamber can reach 800 °C in a matter of milliseconds,) and they produce large volumes of hot gas from a small volume of liquid, making hydrazine a fairly efficient thruster propellant with a vacuum specific impulse of about 220 seconds. Reaction 3 is endothermic and so reduces the temperature of the products, but also produces a greater number of molecules. The catalyst structure affects the proportion of the NH3 that is dissociated in Reaction 3; a higher temperature is desirable for rocket thrusters, while more molecules are desirable when the reactions are intended to produce greater quantities of gas.
Other variants of hydrazine that are used as rocket fuel are monomethylhydrazine, (CH3)NH(NH2) (also known as MMH), and unsymmetrical dimethylhydrazine, (CH3)2N(NH2) (also known as UDMH). These derivatives are used in two-component rocket fuels, often together with nitrogen tetroxide, N2O4, sometimes known as dinitrogen tetroxide. These reactions are extremely exothermic, and the burning is also hypergolic, which means that it starts without any external ignition source.
There are ongoing efforts to replace hydrazine along with other highly toxic substances from the aerospace industry. Promising alternatives include hydroxylammonium nitrate, 2-Dimethylaminoethylazide (DMAZ) and energetic ionic liquids.
The Italian catalyst manufacturer Acta has proposed using hydrazine as an alternative to hydrogen in fuel cells. The chief benefit of using hydrazine is that it can produce over 200 mW/cm2 more[clarification needed] than a similar hydrogen cell without the need to use expensive platinum catalysts. As the fuel is liquid at room temperature, it can be handled and stored more easily than hydrogen. By storing the hydrazine in a tank full of a double-bonded carbon-oxygen carbonyl, the fuel reacts and forms a safe solid called hydrazone. By then flushing the tank with warm water, the liquid hydrazine hydrate is released. Hydrazine has a higher electromotive force of 1.56 V compared to 1.23 V for hydrogen. Hydrazine breaks down in the cell to form nitrogen and hydrogen which bonds with oxygen, releasing water. Hydrazine was used in fuel cells manufactured by Allis-Chalmers Corp., including some that provided electric power in space satellites in the 1960s.
A mixture of 63% hydrazine, 32% hydrazine nitrate and 5% water is a standard propellant for experimental bulk-loaded liquid propellant artillery. The propellant mixture above is notable for being one of the most predictable and stable, with a remarkably flat pressure profile during firing. Misfires are usually caused by inadequate ignition. The movement of the shell after a misignition causes a large bubble with a larger ignition surface area, and the greater rate of gas production causes very high pressure, sometimes including catastrophic tube failures (i.e. explosions).
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, coma in humans. Acute exposure can also damage the liver, kidneys, and central nervous system. 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 exposed to hydrazine via inhalation. Increased incidences of lung, nasal cavity, and liver tumors have been observed in rodents exposed to hydrazine.
Limit tests for hydrazine in pharmaceuticals suggest that it should be in the low ppm range. Hydrazine may also cause steatosis. At least one human is known to have died after 6 months of sublethal exposure to hydrazine hydrate.
On February 21, 2008, the United States government destroyed the disabled spy satellite USA 193 with a sea-launched missile, reportedly due to the potential danger of a hydrazine release if it re-entered the Earth's atmosphere intact.
The name "hydrazine" was coined by Emil Fischer in 1875; he was trying to produce organic compounds that consisted of mono-substituted hydrazine. By 1887, Theodor Curtius had produced hydrazine sulfate by treating organic diazides with dilute sulfuric acid; however, he was unable to obtain pure hydrazine, despite repeated efforts. Pure anhydrous hydrazine was first prepared by the Dutch chemist Lobry de Bruyn in 1895.
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|Look up hydrazine in Wiktionary, the free dictionary.|
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- CDC - NIOSH Pocket Guide to Chemical Hazards