Amines Class 12th Notes- Free NCERT Class 12 Chemistry Chapter 13 Notes- Download PDF

What is the first thing that comes to your mind when you are bored or sleepy? An energy drink or maybe a soda? Do you know that coffee contains caffeine, an alkaloid with amine groups? They block sleep-inducing receptors in the brain. This is how active amines are in our daily lives. Amines are vital organic compounds found in many substances, from neurotransmitters and hormones to medicines and industrial chemicals. They are widely found in Proteins, Vitamins, and hormones, and are derivatives of ammonia, where one or more hydrogen atoms are replaced by alkyl or aryl groups.

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This Story also Contains

1. NCERT Class 12 Chemistry Amines Notes
2. Amines
3. Structure of amines
4. Classification of amines
5. Nomenclature
6. Preparation of Amine
7. Physical Properties of Amines:
8. Chemical Reaction of Amines
9. Diazonium Salt
10. Methods of Preparation of Diazonium Salts
11. Physical Properties
12. Chemical Reactions
13. NCERT Class 12 Notes Chapter-Wise
14. Subject Wise NCERT Exemplar Solutions
15. Subject Wise NCERT Solutions
16. NCERT Books and Syllabus

The NCERT Class 12 Chemistry chapter 9 notes cover a brief idea of the chapter on Amines. The prime topics are Amines, their Nomenclature, their Classification, their Preparation, their Physical Properties, their Structure, and their Chemical Reactions. These notes also comprise a brief introduction to diazonium salts, their Physical Properties, their Methods of Preparation, their Chemical Reactions, and their Importance in the Synthesis of Aromatic Compounds.

CBSE Class 12 Chemistry chapter 9 notes cover the basic chemical equations in the chapter. The important structural formulas and chemical equations are included in these notes.

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NCERT Class 12 Chemistry Amines Notes

Amines

When hydrogens in ammonia are replaced by one or more alkyl or aryl groups, amines are formed. They are derivatives of ammonia.

Structure of amines

• Hybridization: sp³
• Geometry: pyramidal
• No. of lone pairs: 1
• Bond angle: less than 109.5°

Classification of amines

On the basis of the number of hydrogen atoms replaced by alkyl or aryl groups in the ammonia molecule amines can be of 3 types:

• Primary
• Secondary
• Tertiary

Nomenclature

Amines are named alkanamines in the IUPAC system. Di, tri, etc prefixes are used depending on the no. of -NH₂ group attached to the carbon chain.

Examples are given in the tabular form:

Preparation of Amine

1. Reduction of nitro compounds

Nitro compounds are reduced to amines in the presence of finely divided Ni, Pd, or Pt & by passing hydrogen gas. Amines can also be prepared by reduction with metals in an acidic medium.

2. Ammonolysis of alkyl halides

Ammonia undergoes a nucleophilic substitution reaction in which a halogen atom is replaced by an amino group. The process by which ammonia molecules cleave the C-X bond is called ammonolysis.

The reactivity order of halides with amines: RI > RBr >RCl

3. Reduction of nitriles

Nitriles on catalytic hydrogenation or reduction with lithium aluminum hydride produce primary amines.

4. Reduction of amides

Amides undergo reduction to produce amines.

5. Gabriel phthalimide synthesis

Gabriel phthalimide synthesis is a reaction that involves the conversion of primary alkyl halides into primary amines using alkyl halides.

6. Hoffmann bromamide degradation reaction

Physical Properties of Amines:

• Primary amines having 3 or more C are liquid & heavier ones are solid.
• Aryl amines are generally colorless but on atmospheric oxidation gain color.
• Amines are polar molecules due to the presence of lone pairs which induce large dipole moments.
• The primary & secondary amines can undergo H bonding. The tertiary amine cannot undergo H bonding but can accept H bonds from N-H or O-H bonds.
• In amines solubility decrease as the molar mass of amines increases. This is because the hydrophobic alkyl part increases in size. Amines with high molecular mass are insoluble in water.
• Boiling point : Ethers (similar molecular weights) < Primary & secondary amine < alcohols ; Primary ≈ Secondary > Tertiary amines

Chemical Reaction of Amines

Amines are reactive due to the presence of electronegativity difference between N & H & the presence of lone pairs.

1. Basic character of amines

Amines react with acid to form salts.

Structure-basicity relationship of amines

(a) Alkanamines versus ammonia

The basicity order of amines in the gaseous phase: 3° amine > 2° amine > 1° amine > ammonia

The basicity order of aliphatic amines: 1° > 2° > 3°

The order of basic strength in case of substituted amines:

$\begin{array}{rl}& {\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_2\mathrm{NH}>{\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_3\mathrm{N}>{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2>{\mathrm{NH}}_3\\ & {\left({\mathrm{CH}}_3\right)}_2\mathrm{NH}>{\mathrm{CH}}_3{\mathrm{NH}}_2>{\left({\mathrm{CH}}_3\right)}_3\mathrm{N}>{\mathrm{NH}}_3\end{array}$

(b) Arylamines vs ammonia

In the case of substituted arylamines, electron-releasing groups like –OCH₃, and –CH₃ increase basic strength whereas electron-withdrawing groups like –NO₂, –SO₃H, –COOH, and –X decrease basic strength.

2. Alkylation

3. Acylation

Aliphatic & aromatic primary & secondary amines undergo nucleophilic substitution reactions with acid chlorides, anhydrides & esters.

4. Carbylamine reaction

$\mathrm{R}-{\mathrm{NH}}_2+{\mathrm{CHCl}}_3+3\mathrm{KOH}\stackrel{\text{ Heat }}{\to }\mathrm{R}-\mathrm{NC}+3\mathrm{KCl}+3{\mathrm{H}}_2\mathrm{O}$

5. Reaction with nitrous acid

(a) Primary aliphatic amines from aliphatic diazonium salts on reaction with nitrous acid.

(b) Aromatic amines form diazonium salts on reaction with nitrous acid at low temperatures.

6. Reaction with aryl sulphonyl chloride

(a) The reaction of benzene sulphonyl chloride yields N-ethylbenzene sulphonyl amide on reaction with a primary amine.

(b) N, N-diethyl benzene sulphonamide is formed in the reaction with a secondary amine with benzene sulphonyl chloride.

(c) Tertiary amines & benzene sulphonyl chloride do not react.

7. Electrophilic substitution

(a) Bromination:

(b) Nitration:

(c) Sulphonation:

Diazonium Salt

The diazonium salts have the general formula – RN₂ + X^- where R stands for an aryl group & X^- ion may be Cl^-, Br^-, HSO₄^-, BF₄^-, etc.

Nomenclature: The name of parent hydrocarbon is added as prefix & name of anion after diazonium. Example: benzenediazonium chloride etc.

1° aliphatic amines form highly unstable alkyl diazonium salts & 1° aromatic amines form arene diazonium salts (stable at low temperature for short time).

Methods of Preparation of Diazonium Salts

The reaction of aniline with nitrous acid produces Benzene diazonium chloride. Diazotization is the term coined for the conversion of primary aromatic amines into diazonium salts.

${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2+{\mathrm{NaNO}}_2+2\mathrm{HCl}\stackrel{273-278\mathrm{K}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{N}}_2^{+}\mathrm{Cl}+\mathrm{NaCl}+2{\mathrm{H}}_2\mathrm{O}$

Physical Properties

• Colorless crystalline solid
• Soluble in water (cold water-stable; warm water - react)
• Decomposes easily in the dry state
• Some diazonium salts like Benzenediazonium fluoroborate are water-insoluble & stable at room temperature.

Chemical Reactions

(A) reactions involving displacement of nitrogen

1. Replacement by halide or cyanide ion:

Also known as the Sandmeyer reaction; involves the nucleophilic substitution of diazonium salt to give aryl halide in presence of Cu(I) ion.

Also known as the Gatterman reaction; involves the nucleophilic substitution of diazonium salt to give aryl halide in the presence of copper powder. Sandmeyer’s reaction is better than Gattermann’s reaction.

2. Replacement by iodide ion:

Iodobenzene is formed when a diazonium salt solution is treated with potassium iodide.

${\mathrm{Ar}}_2^{+}{\stackrel{-}{\mathrm{N}}}_2+\mathrm{KI}⟶\mathrm{ArI}+\mathrm{KCl}+{\mathrm{N}}_2$

3. Replacement by fluoride ion:

Arene diazonium fluoroborate is produced on treating arene diazonium chloride with fluoroboric acid which on heating decomposes to yield aryl fluoride.

${\mathrm{ArN}}_2^{+}\stackrel{-}{\mathrm{Cl}}+{\mathrm{HBF}}_4⟶\mathrm{Ar}-{\stackrel{+}{\mathrm{N}}}_2{\mathrm{BF}}_4\stackrel{\mathrm{\Delta }}{\to }\mathrm{Ar}-\mathrm{F}+{\mathrm{BF}}_3+{\mathrm{N}}_2$

4. Replacement by H:

Diazonium salts are reduced to arenes when treated with ethanol or hypophosphorous acid.

5. Replacement by hydroxyl group:

6. Replacement by –NO₂ group:

The Diazonium group is replaced by the –NO₂ group when the diazonium fluoroborate is heated with aqueous NaNO₂ in the presence of Cu.

B. Reactions involving retention of diazo group

Coupling reactions:

A reaction between Benzene diazonium chloride & phenol results in coupling between two molecules at the para position of phenol via -N=N- bond. P-hydroxyazobenzene is formed as a product.

Azo coupling of sulfanilamide acid & N-(1-Naphthyl)ethylenediamine

Importance of Diazonium Salts in Synthesis of Aromatic Compounds

Diazonium salts are a very good intermediate therefore they are helpful in a reaction where direct substitution is not possible. For example, aryl fluorides, aryl iodides, cyanobenzene, & chlorobenzene can not be prepared by direct substitution but are easily prepared when the diazo group is introduced.

Amines Class 12 notes will be helpful to revise the chapter & to get an idea about the main topics covered in the chapter. Also, this NCERT Class 12 Chemistry chapter 9 notes are useful to cover the main topics of the Class 12 CBSE Chemistry Syllabus & also for competitive exams like VITEEE, BITSAT, JEE Core, NEET, etc.

NCERT Class 12 Notes Chapter-Wise

Subject Wise NCERT Exemplar Solutions

Subject Wise NCERT Solutions

NCERT Books and Syllabus