Chapter 6th:- Preparation Properties & Structures of Borazine, Diborane, Hydrazine, Interhalogens, Polyhalides, and Fluorides of Xenon 1st year Book
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Preparation Properties & Structures Hydrazine or diamine

Molecular formula :N2H4

Structural formula : NH2⋅NH2

Methods of preparation :

Hydrazine is prepared by the following methods.

(1) Raschig’s Process :

This method is used to prepare hydrazine in the laboratory as well as on commercial scale. In this method, hydrazine is prepared when concentrated aqueous solution of ammonia is boiled with sodium hypo-chloride in the presence of glue or gelatine. The reaction takes place in two steps.

Sodium Hypochloride to hydrazineNote : Glue prevents the formation of NHCl2 and NCl3 during this reaction.

Solution from the above reaction is ice cooled. On adding H2SO4, a partially soluble crystalline precipitate of hydrazine hydrogen sulphate separate out. Hydrazine is obtained by heating these crystals with ammonia.

N2H2HSO4 + 2NH3 NH2NH2 + (NH2)2SO4

(ii) Action of NO with potassium Sulphide:

When a solution of K2SO3 is saturated with nitric oxide an addition product is formed which on reduction with amalgam gives hydrazine.

K2SO3 + 2NO K2SO3N2O2 

K2SO3N2O2+6H Reduction −K2SO4+N2H4+H2O

(iii) Hydrazine can also be prepared by reducing hydrazoic acid (N3H) in presence of sodium amalgam or finely divided platinum.

2N3H + 10H Na2Hg 3H4

(iv) Action of sodium methoxide (CH3ONa) on hydrazinium monochloride (N2H5Cl):

An hydrous hydrazine is prepared by adding a solution of sodium methoxide (CH3ONa) in CH3OH to a solution of hydrazinium monochloride, [N2H5]+Cl dissolved in CH3OH. The reaction between [N2H5]Cl and CH3ONa gives a solution which contains N2H4 and CH3OH. When this solution is distilled under pressure, CH3OH gets distilled first and then N2H4.


Physical Properties:

Hydrazine is a colourless liquid, soluble in water and alcohol, it is a very hygroscopic substance, which rapidly absorbs moisture and carbon dioxide from air, its aqueous solution is alkaline. It can dissolve sulphur, selenium, phosphorus and arsenic:

Chemical Properties:

(i) Thermal decomposition:

It decomposes into nitrogen and ammonia on heating.


(ii) As a reducing agent:

Hydrazine is a strong reducing agent and gives nitrogen on oxidation.

(a) Hydrazine is rapidly oxidized when brought in contact with oxygen and chlorine.

N2H4 + O2 N2 + 2H2O

N2H4 + 2C2 N2 + 4HCl

(b) Reaction with O3 and H2O2 : Ozone and hydrogen peroxide oxidizes hydrazine into hydrazoic acid.

3N2H4 + 5O3 2N3H + 5H2O + 5O2

3N2H4 + 5H2O2 2N3H + 10H2O

(c) It reduces various metallic salts into metals.

4AgNO3 + N2H4 4Ag + N2 + 4HNO3

4AuCl3 + 3N2H4 4Au+ 3N2 + 12HCl

4CuO + N2H4 2Cu2O + N2 + 2H2O

4FeCl3 + N2H4 4FeCl2 + N2 + 4HCl

PtCl4 + N2H4 4Pt + N2 + 4HCl

2HgCl2 + N2H4 2Hg + N2 + 4HCl

(d) Acidic potassium permanganate becomes colourless and iodate is reduced to iodide.

4MnO4  +  12H+ +  5N2H4 4Mn2 + 16H2O + 5N2

2IO3+ 3N2H4 21+6H2O+3N2

(e) Action with H2O:

When hydrazine is treated with water in presence of Cu(II) catalyst, it decomposes to give N2, O2 and H2 gas. This reaction is exothermic.

2H2O(I) + N2H4(l) 4H2 + N2 + O2

(iii) Reaction with Nitrous acid:

Hydrazine and nitrous acid react together to form hydrazoic acid.

N2H4 + N2H4(I) 4H2 + N2 + O2

(iv) Reaction with Sodium:

In the absence of oxygen, hydrazine reacts with sodium as given below.

creation of hydrazinum monchloride (salt)

2NH2NH2 + 2Na 2NH2NHNa+ + H2󠄴

(v) Basic Nature :

Hydrazine reacts with acids to form two series of salts. The basic character is attributed to the lone pairs present on nitrogen atoms.

hydryzine is diacidic baseThus, hydrazine is a di-acidic base.

(vi) Formation of complex compounds :

Hydrazine is an example of mono-dentate, bidentate and bridging ligand (a molecule or anion which contain two lone pair of electron is called bidentate ligand), It forms a series of complex compounds on reaction with different transition metal salts. For example :

CoCl3+6N2H4⟶[Co(N2H4)6]Cl3 (when hydrazine acts as a mono-dentate ligand)

CoCl3+3N2H4⟶[Co(N2H4)3]Cl3 (when Hydrazine acts as a bi-dentate ligand) 

(viii) Reaction with carbonyl compounds :

Hydrazine reacts with aldehyde and ketone to form hydrazone.

For example :

(a) Reaction with acetaldehyde:

Acetone, Aldehyde


(i) It in used as a reducing agent.
(ii) As a fuel in rockets.
(iii) As a reagent in organic chemistry.


In hydrazine, each nitrogen is bonded to two hydrogen atoms and other nitrogen atom by single bonds. The lone pairs on nitrogen atoms repel each other and try to remain farthest. Consequently, no free rotation is observed along N−N bond. The lone pairs are also responsible for its basic nature. The N-N and N−H bond distance are Å1.47Å and Å1.04Å respectively and the NNH and HNH bond angles are 110∘.

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