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Chemistry Notes for class 12 Chapter 13
Amines
Amines constitute an important class of organic compounds derived by replacing one or more
hydrogen atoms ofNH 3 molecule by alkyl/aryl group(s)
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The three hybrid orbitals are involved in bond
formation and one hybrid atomic orbital contains the lone pair of electrons, giving the
pyramidal geometry of amines
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However, primary amine is obtained as a major product by taking large excess of NH3
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Aromatic amines could not be prepared since aryl halides are much less reactive towards
nucleophilic substitution reactions
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This method is not suitable for 1° arylamine because aryl halide
does not give nucleophilic substitution reaction
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To obtain primary amine with same number of carbon atoms from primary amide, reduction is
done with LiAlH4/ether
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The lower aliphatic amines are gases with fishy smell
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Primary amines witb three or more carbon atoms are liquid and higher members are all
solids
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Lower aliphatic amines are water suluble because they can form hydrogen bonds with
water molecules, however the solubility decreases with increase in hydrophobic alkyl
group
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Boiling points order primary > secondary > tertiary
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Basic Strength of Amines
Amines act as Lewis bases due to the presence of lone pair of electrons on the nitrogen atom
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Lesser the pKb‘ higher is the basicity of amines
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Among aliphatic methyl amines, the order of basic strength in aqueous solution is as follows
(C2H5NH > (C2H5)3N > C2H5NH2 > NH3
(CH3)2NH > CH3NH2 > (CH3)3N > NH3
Aromatic amines are weaker basesthan aliphatic amlnes and NH3,due to the fact that the
electron pair on the nitrogen atom is involved in resonance with the π-electron pairs of the ring
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) increase the basic strength of aromatic
amines while electron withdrawing groups (like – NO2, -X,-CN etc
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o-substituted aromaticamines are usually weaker basesthan aniline irrespective of the nature of
substituent whether electron releasing or electron withdrawing
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chemical Properties of Amines
(i) Alkylation All the three types of amines react with alkyl halides to form quaternary
ammonium salt as the final product provided alkyl halide is present in excess
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But secondary and _tertiary amines react with nitrous acid in different manner
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(vi) Reaction with aryl sulphonyl chloride [Hinsberg reagent] The reaction of
benzenesulphonyl chloride with primary amine yield N-ethyl benzenesulphonyl amide
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(vii) Reaction with aldehydes Schiff base is obtained
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To prepare monosubstituted derivative, activating effect of -NH2 group must be controlled
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(b) Nitration Direct nitration of aniline is not possible as it is susceptible to oxidation, thus
amino group is first protected by acetylation
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(d) Aniline does not undergo Friedel-Crafts reaction due to salt formation with aluminium
chloride, the Lewis acid, which is used as a catalyst
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behave like a strong deactivating group for further chemical
reaction
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Separation of Mixture of Amines (1°, 2° and 3°)
(a) Fractional distillation This method Is based on the boiling points of amines and is used
satIsfactorily in Industry
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1° amine forms solid dialkyl oxamide (CONHR)2
2° amine forms liquid dialkyl oxamlc ester(CONR2-COOC2H5)
3° amlnes do not react
(c) Hlnsberg’s method see
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Benzene Diazonium Chloride (C6H5N2+;Cl-)
Preparation (Diazotisation reaction)
The excess acid in diazotisation reaction is necessary to maintain proper acidic medium for the
reaction and to prevent combination of diazonium salt formed with the undiazotised amine
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Properties
It is a colourless crystalline solid, soluble in water
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Stability of Arenediazonium salts
It is relatively more stable than the alkyldiazonium salt
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These are the derivatives of RCN
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These are neutral compound with pleasent odour, similar to bitter almonds
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These are soluble in water as well as organic solvents
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These are poisonous but less than HCN
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These are colourless unpleasent smelling liquids
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These are soluble in organic solvents but insoluble in water
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These are named according to IUPAC system as ‘nitro alkane’
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These are colourless pleasent smelling liquids
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Their boiling point are much higher than isomeric alkyl nitriles
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These are less soluble in water but readily soluble in organic solvents
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Nitrobenzene gives different prociucts with different reagents and in different mediums
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This reaction is called Nef carbonyl
synthesis
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It does not give Friedel-Craft’s alkylation
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