CBSE Class 12 Chemistry Notes Chapter 13 Amines

Amines are a class of compounds that are obtained by replacing one or more hydrogen atoms of ammonia molecules with an alkyl group. They are derived either from practice or principal from ammonia.

• Amines contain basic nitrogen atoms with a lone pair of electrons.
• It consists of three hydrogen atoms bonded to nitrogen atoms. 
• Diazonium salts are a type of organic molecule that consists of a diazonium functional group (N²⁺), commonly called diazonium compounds or diazonium ions. 
• This compound is obtained when primary aromatic aminеs react with nitrous acid (HNO₂).
• Classification of amines takes place on the basis of nature and number of nitrogen atoms.
• Amines have a wide range of applications in real life, including their usage in cheese, chocolates, beer, yeast extracts, and fish products.

According to the CBSE Syllabus 2023-24, the chapter on Amines has been renumbered as NCERT Class 12 Chemistry Chapter 9. Amines Notes are given in the article below for preparation for the CBSE Class 12 Chemistry Examination.The chapter helps an individual score six marks in the board exam.

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Amines Notes

Nomenclature of Amines 

The nomenclature of amines includes determining the parent chain of compounds, suffixes of the functional groups, and prefixes of substituent groups.

• The IUPAC name of the amines is known as alkanamines.
• It involves the replacement of the 'e' of alkane with the word amine.
• The attachment of suffixes like di, tri, etc is attached to the compounds.
• The common name of the aliphatic name is done by prefixing the alkyl group to the compound.
• In the case of the secondary and tertiary amine, the arrangement of the alkyl group is in alphabetical order, followed by the compound amine.

Nomenclature of Amines

Classification of Amines

Amines are classified into three groups, namely Primary (1^o Amine), Secondary (2^o Amine), and Tertiary (3^o Amine). 

• Primary amines are formed when one hydrogen atom of ammonia is substituted by the alkyl or aromatic group.
• Secondary amines are formed when the hydrogen atom of ammonia is substituted by the two organic substitutes.
• Tertiary amines are formed when the hydrogen atom of ammonia is substituted by the three organic substitutes.
• Methyl amine, Dimethylamine, and Trimethylamine are some common examples of Primary (1^o Amine), Secondary (2^o Amine), and Tertiary (3^o Amine), respectively.

Classification of Amines

Structure of Amines

The structure of amines is divided into alkyl and aromatic amines.

• Alkyl amines are formed by the tetrahedral nitrogen where the C-N-C and C-N-H bond angle is 109 degrees.
• This class of amines exhibits chiral properties where the centre of nitrogen can create lone pairs.
• Aromatic amines consist of a mixture of the lone pair with the aryl substituent. 
• As a result, nitrogen forms a planar structure.
• In this type of structure, the distance between C-C bonds is greater than C-N bonds. 

Preparation of Amines

Different methods for the preparation of amines are as follows:

• Preparation from Halogenoalkanes: In this process, a mixture of halogenoalkanes is heated in a sealed tube with the solution of ammonia.

CH₃CH₂Br + NH₃ → CH₃CH₂NH₃ + Br^-

• Reduction of Nitriles: In this process, nitriles are treated with a solution of lithium aluminium hydride.

Reduction of Nitriles

• Gabriel Phthalimide Synthesis: In this method, the reaction between phthalimide and a solution of ethanol and potassium hydroxide takes place.

Gabriel Phthalimide Synthesis

Properties of Amines

The properties of physical and chemical amines are as follows:

Physical Properties of Amines

• Amines are highly polar compounds because of the presence of lone pairs of electrons.
• Primary amines are liquid at room temperature, whereas higher amines are solid.
• The boiling point increases with an increase in molecular weight.
• The aromatic class of compounds are less soluble in water.
• An increase in the size of hydrophobic alkyl results in a decrease in the molar weight of the compounds.
• Aliphatic amines are considered more basic in comparison to aromatic amines.

Chemical Properties of Amines

• The basicity of amines depends upon the molecule and the presence of the lone pair of nitrogen electrons.
• Since they are basic in nature, they can easily react with acids to form different compounds.
• Acylation involves reaction between aliphatic and aromatic, primary and secondary amines with acid chlorides, anhydrides and esters.

Acylation

• Benzoylation involves a reaction between methenamine and benzoyl chloride, forming hydrochloric acid and N-methylbenzamide.

Benzoylation

Uses of Amines

• Amines are used in the manufacture of azo dyes.
• The compound is used as a corrosion inhibitor.
• It is used in the manufacturing of medicine and purification of water.
• Amines are used in the preparation of pesticides and insecticides.
• Some medicines like morphine and demerol are prepared using amines.

Preparation of Diazonium Salts

The process of preparation of diazonium salts involves the conversion of primary aromatic amines by a process named diazotization or dissociation.

• The first step is the selection of primary aromatic amine.
• The next step is the acidification of sulfuric acid (H₂SO₄) and hydrochloric acid (HCl).
• Now, sodium nitrite reacts with a strong acid, such as hydrochloric acid, to produce nitrous acid in situ. 
• Next, add the nitrous acid with aromatic amine to undergo diazotization.
• After the process is completed, the diazonium salt is isolated by precipitating it with an appropriate counterion.

Diazonium Salts 

Chemical Reaction of Diazonium Salts

• Coupling Reaction: Coupling reactions involve the production of a new carbon-carbon bond as a result of the interaction of the diazonium salt with a nucleophile. 
• Azo Coupling: Azo Coupling involves the reaction of an aromatic chemical, such as phenols or aromatic amines, interacting with the diazonium salt. 
• Preparation of Benzene Diazonium Hydrogen Sulphate: The preparation of Benzene Diazonium Hydrogen Sulphate involves the reaction of the compound using Sulphuric Acid as the mineral acid. 

Benzene Diazonium Hydrogen Sulphate

Importance in Synthetic Organic Chemistry

Diazonium salt is one of the most important reagents in synthetic organic chemistry because of its numerous uses and properties.

• The salt is used in the synthesis of many organic compounds like aryl derivatives.
• Diazonium salts are used in the production of dyed fabrics.
• The fabric is prepared by an electrophilic substitution process.
• They are used in the preparation of azo dyes.
• It is used to prepare medicines, fine chemicals, agrochemicals, and other complicated organic molecules.
• Diazonium salt acts as an intermediate to introduce bromide, fluoride, chloride, hydroxyl, iodide, and -CN groups to the aromatic ring.

There are Some important List Of Top Chemistry Questions On Amines Asked In CBSE CLASS XII