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CBSE Class 12th Chemistry Notes: Amines (Part - II)

Nov 3, 2016 17:00 IST

    This article provides you the revision notes on Class 12 Chemistry: Chapter - Amines, to give you a quick glance of the chapter. This article is a continuation of the revision notes on Class 12 Chemistry, Chapter - Amines, Part-I. Part-I was all about the introduction to amines along with the methods of preparation of of amines, their physical properties and basicity. In Part-II, you will get to know about the various chemical reactions undergone by the amines. Also this part will make you familiar with Diazonium salts. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 12th Chemistry.

    The main topics covered in this part are:

    •    Amines

         o    Chemical reactions

    •    Diazonium Salt

          o    Introduction

          o    Structure

          o    Preparation

          o    Physical properties

          o    Chemical reactions

    •    Uses of amines

    The key notes of the chapter are as follows:

    Chemical Reactions of Amines

    1. Reaction with acids:

    2. Alkylation:

    Alkylation of 1o amine generates 2o amine, 3o amine and finally the quaternary salts.

    3. Acylation:

    Reaction with acid chlorides, anhydrides and esters by nucleophilic substitution reaction is known as acylation. The reaction is proceeded by the replacement of hydrogen atom of –NH2 or >N–H group by the acyl group (RCOX).

    Tertiary (3o) amine cannot be  acylated as there is no H bonded to nitrogen.

    4. Benzoylation:

    5. Reaction with nitrous acid, HNO2

    Three classes of amines react differently with nitrous acid

    (a) Reaction of 1o amines:

    (b) Reaction of 2o amines:

    (c) Reaction of 3o amines:

    6. Carbylamine reaction:

    Primary amine (both aliphatic and aromatic) reacts with CHCl3/KOH to form isocyanides (carbylamines) with unpleasant smell.

    7.  Reaction with aldehyde and ketones:

    1o amines react with aldehydes and ketones to form Schiff’s bases.

    8. Electrophilic substitution reactions

    Aniline, due to high electron density at ortho and para-positions, is ortho and para directing towards electrophilic substitution reaction.

    Some of the electrophilic substitution reactions of aniline are described below:

    (a) Bromination:

    To prepare monosubstituted aniline derivative, first acetylation of aniline is carried out with acetic anhydride followed by the desired substitution of the substituted amide which is then hydrolysed to obtain the monosubstituted amine.

    (b) Nitration:

    To get p-nitro derivative as major product, acetylation of aniline is carried out with acetic anhydride. Then desired substitution of anilide is carried out followed by hydrolysis of the substituted anilide to the substituted amine.

    Diazonium Salts

    Structure of Diazonium Salt

    Preparation of Diazonium Salt

    The reaction of preparation of diazonium salt is called Diazotisation.

    Physical Properties of Diazonium Salt

    •    It is a colourless crystalline solid.

    •    It is readily soluble in water and is stable in cold but reacts with water when warmed.

    •    It has tendency to explode when dry.

    Chemical Reactions of Diazonium Salts

    There are two types of reactions given by benzene diazonium chloride.

    (1)Substitution reactions involving replacement of diazonium group.

    (2) Coupling reactions involving the retention of diazo group acts as an electrophile.

    Explanation:

    1. Substitution reactions involving replacement of diazonium group:

    (a)  Replacement by halide or cyanide ion:

    Above reaction taking place in the presence of Cu(I) ion is called Sandmeyer reaction.

    Above reaction taking place in the presence of copper powder is named as Gatterman reaction.

    (b) Replacement by iodide ion:

    (c) Replacement by fluoride ion:

    (d) Replacement by H-atom:

    (e) Replacement by hydroxyl group:

    (f) Replacement by –NO2 group:

    2. Reactions involving retention of diazo group

    Coupling recations:

    Uses of Amine

    •   The most important amie is aniline which is used in the synthesis of medicines, dyes, etc
    •   N , N – Dmethylaniline (DMA) also used in the preparation of Methyl orange and other dyes
    •   Amines are widely used in developing chemicals for crop protection and water purification
    •   1, 6 – Hexamethylenediamine H2N ‒ (CH2)6 ‒ NH2 is used in the production of nylon
    •   Adrenaline is an amine hormone that prepares the human beings for emergency situation
    •   Amino acids form the building blocks of proteins in human beings

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