Hydrazine

Hydrazine or hydrazine is a chemical compound whose condensed chemical formula is N₂H₄.

It is a colorless, oily liquid with an ammonia-like odor that releases vapors when exposed to air. Burns with barely visible flame. It is supplied commercially in aqueous solution or as hydrazine hydrate (H₂N−NH₂ H₂O).

It is mainly used as a foaming agent for the preparation of polymeric foams as well as a precursor for polymerization catalysts and drugs. Additionally, it is used as fuel for airplanes, missiles, space rockets, and satellites. The oxidizer used in these cases is usually dinitrogen tetrahydride. Compounds derived from it are also known as hydrazines.

As a general rule, hydrazine is not used as fuel, but rather one of its derivatives such as methylhydrazine or asymmetric dimethylhydrazine. The use of the latter entails important advantages, such as being storable at room temperature and igniting as soon as they come into contact with the oxidizer (this type of fuel is called hypergolic). However, due to its high toxicity, its use has tended to be abandoned.

It is important to mention that this chemical compound reacts with oxygen in the following way: N₂H₄ + O2 → N2 + 2 H2O, reducing the possibility of oxidation corrosion in metals. In addition, when it comes into contact with ferric oxide, it generates magnetite, water and nitrogen: N₂H₄ + 6 Fe2O3 → 4 Fe3O4 + 2 H2O + N2.

Theodor Curtius first synthesized free hydrazine in 1889 through a circuitous process.

Molecular structure and properties

Hydrazine forms a monohydrate that is more dense (1.032 g/cm³) than the anhydrous material.

Hydrazine can arise through the bonding of a pair of ammonia molecules through the removal of a hydrogen molecule. Each H 2 N-N subunit is pyramidal in shape. The NN distance is 1.45 Å (145 pm), and the molecule adopts a gauche conformation. The rotation barrier is twice that of ethane. These structural properties are similar to those of gaseous hydrogen peroxide, which adopts an "oblique" anticlinal conformation, and also possesses a high rotational barrier.

Hydrazine has basic (alkaline) chemical properties similar to those of ammonia:

N₂H₄ + H₂O → [N₂H₅]⁺ + OH⁻

with the values:

K_b = 1.3 x 10⁻⁶

pK_a = 8.1

(For ammonia K_b = 1.78 x 10⁻⁵) Hydrazine is difficult to diprotonate:

[NON]₂H₅]⁺ + H₂O → [N₂H₆]²⁺ + OH⁻ K_b = 8.4 x 10⁻¹⁶

The heat of combustion of hydrazine in oxygen (air) is 194.1 x 10⁵ J / kg.

Synthesis and manufacturing

Hydrazine is produced by Olin Raschig's process in which sodium hypochlorite (the active ingredient in many bleaches) is reacted with ammonia, this process was disclosed in 1907. This method is based on the reaction of chloramine with ammonia:

NH₂Cl + NH₃ → H₂N-NH₂ + HCl

Another synthesis route for hydrazine involves the oxidation of urea with sodium hypochlorite:

(H₂N)₂C=O + NaOCl + 2 NaOH → N₂H₄ + H₂O + NaCl + Na₂CO₃

Hydrazine can be synthesized from ammonia and hydrogen peroxide in the Pechiney-Ugine-Kuhlmann process, according to the following formula:

2NH₃ + H₂O₂ → H₂N-NH₂ + 2H₂O

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

Hydrazine can also be produced through the so-called ketazine and peroxide processes.

Dangers

Hydrazine is highly toxic and dangerously unstable, especially in the anhydrous form. According to the US Environmental Protection Agency:

Acute (short-term) symptoms of exposure to high levels of hydrazine may include eye, nose and throat irritation, dizziness, headache, nausea, pulmonary edema, seizures, coma in humans. Acute exposure can also damage the liver, kidneys, and central nervous system. Liquid is corrosive and can produce skin contact dermatitis in humans and animals. Effects have been observed in lungs, liver, spleen and thyroid in animals chronically exposed to hydrazine by inhalation. There is also a correlation between exposure to hydrazine and an increase in the incidence of lung cancer, nasal cavity and liver tumors.

Limit testing of hydrazine in pharmaceuticals suggests it should be in the ppm range. Hydrazine can also cause steatosis. At least one human is known to have died, after 6 months of sublethal exposure to hydrazine. hydrazine.

On February 21, 2008, the United States of America destroyed a spy satellite, also American, that was out of control, claiming that its fuel tank was full of hydrazine and that it could spread over some populated area.

On February 29, 2008, an accident involving two trucks carrying hydrazine occurred in San Carlos de Bariloche, a city in Argentina that belongs to the province of Río Negro, and is the head of the Department of Bariloche. There were no injuries, although one of the drivers had dizziness from inhaling that substance.