Download AMINES

UNIT ─ 13
AMINES
GIVE REASONS:Q1) In the reduction of nitroalkanes to corresponding alkanamines iron scrap and HCl is
preferred as reducing reagent.
Ans) This is because FeCl2 formed gets hydrolysed to release HCl in the reaction. Thus, only a
small amount of HCl is required to initiate the reaction.
Q2) Ammonlysis of R-X is not a preferred method for preparing amines
Ans) This method yields a mixture of primary, secondary, tertiary a mines and also quaternary
ammonium salt which need to be separated
Q3) Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis
Ans) Because aryl halides do not undergo nucleophilic substitution since C-X bond has partial
double character due to resonance and is difficult to break.
Q4) Lower aliphatic amines are soluble in water.
Ans) because they can form hydrogen bands with water molecules
Q5) Higher amines are essentially insoluble in water
Ans) Due to hydrophobic interactions of larger alkyl gramp
Q6) Butan-1-ol is more soluble in water than butan-1-amine
Ans) Butan-1-ol is more polar due to higher electronegitivity of oxygen companed to nitrogen
Q7) The order of boiling points of isomeric amines is Primary > Secondary > Tertiary
Ans) (last paragraph page 387)
Q8) Boiling points n-C4H9OH is higher than of n-C4H9NH2.
Ans) Though both have intermolecular H bond .The H bond between alcohol molecules are
stronger owing to the higher polarity of O – H bond compared to N – H bond.
Q9) Aliphatic amines are stronger bases than NH3.
Ans) In both NH3 and amines there is an unshared pair of electrons on N atom due to which they
behave as Lewis base. Due to electron donating inductive effect (+I) effect of alkyl groups
electron density on N increases making amines stronger Lewis base than NH3.
R  NH 2
Q10) Aromatic amines are less basic than NH3
Ans) Election withdrawing aryl group (benzene ring) reduce elections density on N.
Q11) The order of basicity of amines in a gaseous phase is 3o > 2o > 1o.
Ans) Electron releasing alkyl group (+I effect) pushes electrons towards N and thus makes the
unshared electron pair more available for sharing with the proton of the acid. So, basic nature
increases with increase in number of alkyl groups.
Q12) The order of basicity of amines in aqueous solutions is in the order 2o > 1o > 3o>NH3.
Ans) In aqueous phase besides +I effect of alkyl groups hydration of substituted ammonium
cations and steric factors affect base strength. Order of stability of ammonium cation by
hydration (solvation)is 1o> 2o > 3o because RNH3+ has more -Hydrogen than R2NH2+, which
has more than R3NH+ .Moreover larger and more number of alkyl groups also cause steric
hindrance to formation of H bonds with water.
Q13) The order of base strength in aqueous solution for ethyl substituted amines is in this order
(C2H5)2NH > (C2H5)3N > C2H5NH2 > NH3
while for methyl substituted amines it is
(CH3)2NH > CH3NH2 > (CH3)3N
> NH3
Ans) Due to higher +I effect of Ethyl group
Q14) The order of base strength in aromatic amines is :
2,4-Dimethoxyaniline > p-toluidine > aniline > p-Nitroaniline
Ans) Electron releasing groups like –OCH3 , CH3 etc increase electron density on N and increase
base strength while electron withdrawing groups like – NO2 , -COOH , -X etc decrease base
strength . Moreover, more the number of electron releasing groups stronger is the base.
Q15) Acylation reaction of amines is carried out in the presence of a base like pyridine which is
a stronger base than amine.
Ans) The base removes HCl formed and shifts the equilibrium of the reaction to the right side
(LeChattelier’s Principle).
pyridine
C2H5NH2 + CH3COCl
C2H5NHCOCH3 + HCl
Q16) The product obtained when benzenesulphonyl chloride (Hinsberg’s reagent) reacts with a
primary amine is soluble in alkali. But the product obtained when secondary amine reacts in a
similar manner is not.
Ans) The H attached to N is acidic due to the presence of strong e withdrawing sulphonyl group.
So it forms salt with alkali and dissolves. In the case of sec-amines there is no H attached to N so
the product does not dissolve in alkali.
Q17) pKb of aniline is more than that of methylamine
Ans) Higher the pKb value, weaker the base. Aniline is a weaker base because e withdrawing
benzene ring reduces e density on N so the lone pair of electrons on N is less readily available
for protonation while CH3 group in methyl amine is election releasing and it increase e density
on N.
Q18) Ethyl amine is soluble in water whereas aniline is not
Ans) Ethyl amine can form H- bonds with water but the larger phenyl group causes hydrophobic
interactions.
Q19) Methyl amine in water reacts with ferric chloride to precipitate ferric hydroxide Fe(OH)3
Ans) Methyl amine being basic liberates OH─ ions in water which causes precipitation of
Fe(OH)3
CH3NH2(aq) + H2O(l) → CH3NH3+ (aq) + OH─(aq)
FeCl3(aq) + OH─ (aq) → Fe(OH)3 (s) + Cl─(aq)
Q20) Amines are less acidic than alcohols of comparable molecular masses
Ans) Due lower electro-negativity of N compared to oxygen N-H bond is less polar than O-H
bond.
Q21) Gabriel phthalimide synthesis is preferred for synthesizing only primary amines.
Ans) This method yields only primary amines and not 2o & 3o amines. Moreover phthalic acid
obtained can be used to prepare phthalimide.
Q22) Anilines react with bromine water to form 2,4,6-tribromoaniline.
Ans) -NH2 is a highly activating group; so electrophilic substitutions occur at all ortho & para
positions.
Q23) Aniline is first acetylated before bromination to yield 4-Bromoaniline.
Ans) This is to reduce the activity of -NH2 group by acetylation.
The lone pair of electrons on N of acetanilide interacts with oxygen atom due to resonance. So
activating effect of ─ NHCOCH3
Group is less than that of ─NH2 group
Q24) Although amino group is o,p-directing in aromatic electrophilic substitution reactions,
aniline on nitration gives a substantial amount of m-Nitroaniline also.
Ans) During nitration aniline being basic is protonated to form anilinium ion which is a
deactivating group and hence m-directing.
Q25) Aniline does not undergo Friedel-Craft’s reaction.
Ans) Aniline being basic forms a salt with AlCl3, which is a Lewis acid. Due to this, nitrogen of
aniline acquires positive charge and hence acts a strong deactivating group.
Q26) Diazonium salts of aromatic amines are more stable than those of aliphatic amines.
Ans) This because aromatic diazonium salts are resonance stabilized.
Q27) Precipitate of AgCl dissolves in aqueous solution of amines.
Ans. Due to the presence of lone pair of electrons on the N atom the amines can act as ligands
and form soluble complexes.
AgCl(s) + CH3NH2(aq) → [Ag(CH3NH2)2]+ Cl─
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CONVERSIONS
1. CH3COOH to CH3CH2COOH

2O / H
CH 3COOH LiAlH
4  CH 3CH 2OH SOCl
2  CH 3CH 2Cl KCN

 CH 3CH 2CN H

 CH 3CH 2COOH
2. Methanamine to Ethanamine
2 / HCl / H 2O
2 / Ni
CH 3 NH 2 NaNO

  CH 3OH SOCl
2  CH 3Cl KCN

 CH 3CN H
 CH 3CH 2 NH 2
3. Nitromethane to Dimethylamine
3Cl
CH 3 NO2 Fe
/ HCl
 CH 3 NH 2 CH

 CH 3 NHCH 3
4. Propanoic acid to Ethanoic acid
NH 3 / 
NaOH / Br2
CH 3CH 2COOH 
 CH 3CH 2CONH 2 
 CH 3CH 2 NH 2
KMnO4 ( O )
NaNO2 / HCl / H 2O
CH 3COOH 
 CH 3CH 2OH 

5. Nitrobenzene to Benzoic acid
6. Benzene to 3-Bromophenol
7. Benzoic acid to aniline
8. Aniline to 2,4,6-tribromofluorobenzene
9. Benzyl chloride to 2-Phenylethanamine
10. Chlorobenzene to 4-Chloroaniline
11. Aniline to 4-Bromoaniline
12. Benzamide to toluene
13. Aniline to Benzyl alcohol
14. Aniline to 1,3,5-Tribromobenzene
15. Ethanoic acid to Methanamine
NH 3 / 
KOH / Br2 , NaOH / Br2
CH 3COOH 
 CH 3CONH 2 

 CH 3 NH 2
16. CH3(CH2)4CN to CH3(CH2)4NH2

/
Br2
3O
CH 3 (CH 2 ) 4 CN H
 CH 3 (CH 2 ) 4 COOH NH
3
 CH 3 (CH 2 ) 4 CONH 2 NaOH
/ 
 CH 3 (CH 2 ) 4 NH 2
17. Methanol to Ethanoic acid

KCN
H 2O / H
CH 3OH SOCl
2  CH 3Cl 
 CH 3CN 

 CH 3COOH
18. Ethanamine to Methanamine
/
Br2
2 / HCl / HONO
4 (O )
CH 3CH 2 NH 2 NaNO

   CH 3CH 2OH KMnO

 CH 3COOH NH
3
 CH 3CONH 2 NaOH
 / 
 CH 3 NH 2