What is Hydrazine?
Hydrazine is an inorganic compound that is also a simple pnictogen hydride with a chemical formula N2H4 that has ammonia like order and is a colourless flammable liquid. Unless it is handled in a solution like that of the NH2NH2· xH2O, it is highly toxic in nature. The hydrazine hydrate market in the world accounted for $350 million in the year 2015. Hydrazine is primarily used as a foaming agent for the preparation of polymer foam. But it is also used as a precursor to polymerisation catalysts, pharmaceuticals, and agrochemicals, along with long-term propellant that could be stored is primarily applicable for the in-space spacecraft propulsion.
Each subunit of H2N-N is pyramidal in molecular structure. As the molecule adopts a gauche conformation, the bond distance of the N-N single bond is calculated which is equal to .45 Å (145 pm). The rotational barrier is observed to be twice that of ethane. These structural properties resemble the gaseous hydrogen peroxide as it is seen to be adopting anticlinal conformation that is skewed in nature and therefore is bound to experience a strong rotational barrier.
In 2015, the foam blowing agent used up about two million tons of hydrazine hydrate. It is also used for the preparation of gas precursors that are used in airbags and is primarily used in rocket fuel of various kinds. For both nuclear and conventional electric power plants, hydrogen is used as an oxygen scavenger that controls the concentration of dissolved oxygen for reducing corrosion. Hydrogen thus refers to a group of organic substances that are derived when one or more hydrogen atoms are replaced in hydrogen by some organic groups.
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Properties of Hydrazine
Physical Properties | |
Properties | Values |
N2H4 chemical name | Hydrazine |
Hydrazine formula | N2H4 |
The molecular weight | 32.0452 g/mol |
Appearance | Colourless, fuming, oily liquid |
Odour | ammonia-like |
Density | 1.021 g/cm3 |
Melting Point | 2 °C; 35 °F; 275 K |
Boiling point | 114 °C; 237 °F; 387 K114 °C; 237 °F; 387 K |
Solubility in water | Miscible |
N2H4 structure | (Image will be Uploaded soon) |
logP | 0.67 |
Vapour pressure | 1 kPa (at 30.7 °C) |
Acidity | 8.10 (N2H5+) |
Basicity | 5.90 |
Conjugate acid | Hydrazinium |
Refractive index | 1.46044 (at 22 °C) |
Viscosity | 0.876 cP |
Structural properties | |
Molecular shape | Triangular pyramidal at N |
Dipole moment | 1.85 D |
Thermochemistry | |
Specific Heat Capacity | 25.23 g-cal/mol-deg |
Standard Molar entropy | 121.52 J/K mol |
Standard enthalpy of formation | 50.63 kJ/mol |
Synthesis of Hydrazine
The key route of the diverse route that has been developed for the synthesis of hydrazine is the creation of an N-N single bond. Out of the many routes that have been developed over a period of time, they are categorised broadly into two major parts. One that uses chlorine oxidants and results in the generation of salts and one that does not.
Oxidation of Ammonia via Oxaziridines from Peroxide
Hydrogen is developed by the reaction of ammonia with hydrogen peroxide in the presence of a ketone catalyst. It is a procedure known as the peroxide process. It is also sometimes referred to as the Pechiney y-Ugine-Kuhlmann process, the Atofina–PCUK cycle, or ketazine process. The net reaction is as follows:-
2 NH3 + H2O2 → N2H4 + 2 H2O
By this route, the imine is first produced by the condensation of ketone and ammonia, which is then oxidised by hydrogen peroxide in order to produce oxaziridine. It is a three-member drink that contains carbon, Oxygen and nitrogen. By the treatment of ammonia, hydrogen is produced from oxaziridine. This process results in the formation of a single nitrogen bond. Therefore the hydrazone condenses with one or more equivalent of the ketone.
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The Azeem that is formed undergoes hydrolysis to give hydrogen name and the regeneration of the ketone, the methyl ethyl ketone.
ME(Et)CNNC(Et)ME + 2H2O → 2ME(Et)CO + N2H4
Chlorine Based Oxidations
Sodium hypochlorite which is an active ingredient in many beeches along with ammonia without the use of any ketone catalyst is the main product that results in the formation of hydrazine. The process is known as the Olin Raschig process, which was first introduced in the year 1907. This method depends on the reaction of mono chloro amine with ammonia that creates the nitrogen-Nitrogen single bond with HCl as a byproduct. The reaction is as follows:-
NH2Cl + NH3 → H2NNH2 + HCl
In the above process, urea can also be oxidised in place of ammonia. In the case of urea as well, sodium hypochlorite serves as an antioxidant. The following reaction is as follows.
(H2N)2CO + NaOCl + 2NaOH → H2NNH2 + NaCl + H2O + Na2CO3.
This process is mainly practised in Asia as it produces a significant amount of by-products. The predecessor of the peroxide process is the Bayer kitazin process. This process incorporates sodium hypochlorite in place of hydrogen peroxide as an oxidant. For each equivalent of hydrogen and equivalent of salt is produced by this method like all the hypochlorite based routes.
Hydrazine Uses
The hydrogen uses are as follows:-
For several pharmaceuticals and pesticides, hydrogen acts as a precursor. These applications often involve the conversion of hydrazine into heterocyclic rings such as pyridazine and pyrazoles. Some examples of the bioactive hydrogen derivatives that have been commercialized include hydrazine sulphate, diimide, triadimefon, cefazolin, rizatriptan, anastrozole fluconazole, metazachlor, metamitron, metribuzin, paclobutrazol, diclobutrazole, propiconazole and dibenzoylhydrazine.
Hydrazine is majorly used as a blowing agent. Specific compounds are known as azodicarbonamide and azobisisobutyronitrile produces 100–200 mL of gas per gram of precursor. When hydrazine reacts with the sodium nitrite it results in the formation of gas that is a reagent in air-bags.
It was used as a component of the rocket fuel in world war II. it is also used as a precursor to polymerisation catalysts, pharmaceuticals, and agrochemicals, along with long-term propellant that could be stored is primarily applicable for the in-space spacecraft propulsion.
FAQs on Hydrazine
1. What is hydrazine and what is its chemical formula?
Hydrazine is an inorganic compound, a simple pnictogen hydride that is a colourless, flammable liquid with an ammonia-like odour. Its chemical formula is N₂H₄. It consists of two nitrogen atoms linked by a single covalent bond, with each nitrogen atom also bonded to two hydrogen atoms.
2. What is the molecular structure of hydrazine (N₂H₄)?
The molecular structure of hydrazine features an N-N single bond, with each nitrogen atom having a trigonal pyramidal geometry. The molecule adopts a staggered, gauche conformation to minimise the repulsion between the lone pairs of electrons on the adjacent nitrogen atoms. This structure is somewhat similar to that of gaseous hydrogen peroxide.
3. What are the main uses of hydrazine in industry and space exploration?
Hydrazine has several important applications based on its chemical properties. The main uses include:
- Rocket Propellant: It is used as a high-energy monopropellant or as a component in bipropellants for rocket and spacecraft thrusters.
- Blowing Agent: It is a precursor for foaming agents, like azodicarbonamide, used to manufacture polymer foams.
- Oxygen Scavenger: In boilers for power plants and heating systems, it removes dissolved oxygen from water to prevent corrosion.
- Chemical Synthesis: It is a key reactant in the production of many pharmaceuticals, pesticides, and polymerisation catalysts.
4. How is hydrazine commercially prepared?
The two main industrial methods for preparing hydrazine are:
- The Peroxide Process: This is a modern, environmentally cleaner method that involves the reaction of ammonia with hydrogen peroxide in the presence of a ketone catalyst. The main byproduct is water.
- The Olin Raschig Process: This older method involves the oxidation of ammonia with sodium hypochlorite (NaOCl). Its key intermediate is monochloramine (NH₂Cl), which then reacts with more ammonia to form hydrazine.
5. What is the oxidation state of nitrogen in hydrazine?
The oxidation state of nitrogen in hydrazine (N₂H₄) is -2. Since hydrogen typically has an oxidation state of +1, we can calculate the oxidation state (x) for each nitrogen atom using the formula: 2x + 4(+1) = 0. This simplifies to 2x = -4, so x = -2.
6. Why is hydrazine a weaker base than ammonia?
Hydrazine (N₂H₄) is a weaker base than ammonia (NH₃) due to the -I (negative inductive) effect. In hydrazine, each nitrogen atom is bonded to another electronegative nitrogen atom via the -NH₂ group. This group pulls electron density away from the adjacent nitrogen's lone pair, making it less available for donation to a proton (H⁺) compared to the lone pair in ammonia, which has no such effect.
7. Why is hydrazine a powerful reducing agent and used as rocket fuel?
Hydrazine is a powerful reducing agent because its nitrogen atoms are in a low oxidation state (-2) and can be easily oxidised to the very stable nitrogen gas (N₂), where the oxidation state is 0. This oxidation is a highly exothermic process, releasing a large amount of energy. When used as a rocket fuel, its combustion produces a large volume of hot gases (N₂ and H₂O), creating the powerful thrust needed for propulsion.
8. What is the difference between the Peroxide process and the Olin Raschig process for synthesising hydrazine?
The primary difference lies in the oxidising agent used and the byproducts formed, which has environmental and economic implications.
- The Peroxide process uses hydrogen peroxide (H₂O₂) as the oxidant. Its main byproduct is water, making it a 'greener' and more atom-efficient process.
- The Olin Raschig process uses sodium hypochlorite (NaOCl) as the oxidant. This process generates a significant amount of salt (NaCl) as a byproduct, which requires costly separation and disposal.
9. Given its toxicity, why is hydrazine still used and what are the necessary safety precautions?
Despite being highly toxic and a potential carcinogen, hydrazine continues to be used because of its unique and highly effective properties for which there are few practical substitutes, especially as a high-energy rocket fuel and an efficient oxygen scavenger. Strict safety protocols are therefore mandatory for its handling. These include using it only in closed systems, ensuring powerful ventilation, and requiring personnel to wear full personal protective equipment (PPE), including respirators and chemical-resistant clothing.
10. How does hydrazine's structure, with its N-N single bond, contribute to its instability?
The instability of hydrazine is primarily due to two structural factors. Firstly, the N-N single bond is relatively weak and susceptible to cleavage. Secondly, the presence of lone pairs of electrons on adjacent nitrogen atoms results in significant electrostatic repulsion. This inherent repulsion makes the molecule energetically unstable and prone to decomposing exothermically into more stable products like nitrogen gas (N₂) and ammonia (NH₃).
