Hydrazine, ไฮดราซีน

ไฮดราซีน, Hydrazine, ไฮดราซีนไฮเดรต, ไฮดราซีนไฮเดรท, Hydrazine Hydrate, N2H2

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 2002, approximately 260,000 tons were manufactured annually. 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.

Applications

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.

 Organic chemistry

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.

Hydrazone formation

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 synthesis. 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.

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

Wolff-Kishner reduction

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.

Heterocyclic chemistry

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.

Sulfonation

Being a good nucleophile, N2H4 can attack sulfonyl halides and acyl halides. The tosylhydrazine also forms hydrazones upon treatment with carbonyls.

Deprotection of phthalimides

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.

Reducing agent

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.

Hydrazinium salts

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,

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.[citation needed

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.[citation needed]

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,[31] which causes it to decompose into ammonia, nitrogen gas, and hydrogen gas according to the following reactions:[citation needed]

 1.3 N2H4 → 4 NH3 + N2

 2.N2H4 → N2 + 2 H2

 3.4 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[citation needed].

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.

Fuel cells

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.

Gun propellant

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).

Hydrazine hydrate is widely used as a reducing agent or an intermediate of synthesis in various industrial sectors like water treatment (effluents, industrial boilers), chemical treatment process (metals, mine extraction) or active ingredients synthesis (pharmaceuticals and agrochemicals).

Hydrazine hydrate is marketed as a water-based solution at different hydrazine concentration

Hydrazine derivatives are used in the manufacture of herbicides and fungicides, as well as plant growth regulators. From tranquilizers to the primary drug for controlling tuberculosis, hydrazine derivatives have proven to be effective ingredients for a number of pharmaceuticals. Used as an oxygen scavenger in boiler water, 35% hydrazine solution reduces oxidation in both low and high pressure steam systems.

In fact, hydrazine is the best material that can be used for protection against oxidation in super critical boilers operating at pressures up to 3500 psi.

Currently, the plastics industry uses hydrazine derivatives in the creation of blowing agents and polymerization initiators. Use of these derivatives is also being investigated for the formulation of polymers.

Terminology
Hydrazine solution strength is usually given as the percent contained hydrazine. However, when hydrazine and water are mixed, a monohydrate (N2H4.H20) is formed through hydrogen bonding. Therefore, the amount of hydrazine in a solution can also be designated as the percentage of hydrazine monohydrate. There is a simple relationship between the two designations, based on their molecular weights.

Hydrazine has a molecular weight of 32 and the monohydrate has a molecular weight of 50. The ratio of their weight is 32/50 or 0.64. Therefore, 100% monohydrate would contain 32/50 or 64% hydrazine. This is the reason 100% hydrazine hydrate can be used interchangeably with 64% contained hydrazine by weight.

To avoid confusion caused by dual terminology, always expresses hydrazine content in terms of contained hydrazine. Since other companies may not follow this convention, users should ascertain which terminology applies when reference to hydrazine solution concentration is involved.

Uses: This product is widely used in the manufacture of pure metal, the thermal power plant boiler antioxidant, synthetic fibers, dyes, imaging, restore, and other chemicals, pigments, resin, food, defense industry, scientific research, organic synthesis, pesticides and raw material of manufacturing intermediates of AC foaming agent .

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