Chapter 8 : Amine

Class 12 Chemistry Chapter 8 Amines Internal Questions and Answers

13.1 Classify the following amines as primary, secondary or tertiary:

Answer : (i) Primary (1°)    (ii) Tertiary (3°)   (iii) Primary  (1°)  (iv) second (2°)

13.2 (i) Write structures of different isomeric amines corresponding to the molecular formula,  .

(ii) Write IUPAC names of all the isomers.

(iii) What type of isomerism is exhibited by different pairs of amines?

Answer : (i) There are eight possible isomeric structure of  .

 (a)   

(b)

(c)

     

(d)

    

(e)

      

(f)

   

(g)

(h)

  

(ii)  (a) Butan-1-amine      (b) 2-methyl Butan-1-amine     (c) Butan-2-amine   (d) 2-methyl Butan-2-amine      (e)  N-Ethylethanamine    (f) N-methyl propan-1-amine      (g) N-methyl propan-2-amine   (h) N,N-dimethylethanamine

(iii) The isomers exhibit structural isomerism. Structural isomerism arises due to the different arrangements of atoms in the molecules. In this case, the butylamine, isobutylamine, and sec-butylamine have different structures but the same molecular formula C₄H₁₁N, making them structural isomers.

13.3 How will you convert

(i) Benzene into aniline (ii) Benzene into N, N-dimethylaniline

(iii)   into hexan-1,6-diamine?

Answer :  (i) Benzene into Aniline:

React benzene with concentrated nitric acid (HNO₃) and sulphuric acid (H₂SO₄) to form nitrobenzene.

 

Reduce nitrobenzene using tin (Sn) and hydrochloric acid (HCl) or catalytic hydrogenation (H₂/Pd) to form aniline.

(ii) Benzene into N, N-Dimethylaniline

React benzene with concentrated nitric acid (HNO₃) and sulphuric acid (H₂SO₄) to form nitrobenzene.

 

Reduce nitrobenzene using tin (Sn) and hydrochloric acid (HCl) or catalytic hydrogenation (H₂/Pd) to form aniline.

React aniline with methyl iodide (CH₃I) or dimethyl sulphate ((CH₃)₂SO₄) in the presence of a base (NaOH) to form N, N-dimethylaniline.

(iii) Cl-(CH₂)₄-Cl into Hexan-1,6-diamine

React 1,4-dichlorobutane with sodium cyanide (NaCN) to replace the chlorine atoms with cyano groups (-CN).

Cl-(CH₂)₄-Cl + 2NaCN → NC-(CH₂)₄-CN + 2NaCl

Reduce adiponitrile using hydrogen gas (H₂) in the presence of a catalyst (e.g., Raney nickel or Pd/C) to convert the nitrile groups (-CN) into primary amine groups (-NH₂).

NC-(CH₂)₄-CN + 4H₂ → H₂N-(CH₂)₆-NH₂   

13.4 Arrange the following in increasing order of their basic strength:

(i)   , ,  ,  ,

(ii)  ,  ,  ,

(iii)  ,  ,  ,  ,

Answer:  Increasing order of their basic strength:

(i)   <  <  <  <

(ii)   <  <   <

(iii)   <  <   <  <

13.5 Complete the following acid-base reactions and name the products:

(i)

(ii) 

Answer : The completed acid-base reactions along with the names of the products:

(i) CH₃CH₂CH₂NH₂ + HCl → CH₃CH₂CH₂NH₃⁺Cl⁻

Product: Propylammonium chloride (n-Propylammonium chloride)

[ Explanation: Propylamine (CH₃CH₂CH₂NH₂) is a weak base. It reacts with hydrochloric acid (HCl), forming propylammonium chloride, a salt where the amine group gains a proton (NH₃⁺) and pairs with a chloride ion (Cl⁻).]

(ii) (C₂H₅)₃N + HCl → (C₂H₅)₃NH⁺Cl⁻

Product: Triethylammonium chloride

[ Explanation: Triethylamine ((C₂H₅)₃N) is a tertiary amine. It reacts with hydrochloric acid (HCl) by accepting a proton, forming triethylammonium chloride, a salt in which the amine is protonated (NH⁺) and paired with a chloride ion (Cl⁻).]

13.6 Write reactions of the final alkylation product of aniline with excess of methyl iodide in the presence of sodium carbonate solution.

Answer: When aniline (C₆H₅NH₂) is treated with an excess of methyl iodide (CH₃I) in the presence of sodium carbonate (Na₂CO₃) solution, successive alkylation occurs, leading to the formation of a quaternary ammonium salt or tetramethylphenylammonium iodide (C₆H₅N(CH₃)₃⁺ I⁻) as the final product. The reaction proceeds through the following steps:

 

 

13.7 Write chemical reaction of aniline with benzoyl chloride and write the name of the product obtained.

Answer:  When aniline (C₆H₅NH₂) reacts with benzoyl chloride (C₆H₅COCl) in the presence of a base like pyridine or sodium hydroxide (NaOH), an acylation reaction (Schotten-Baumann reaction) occurs, forming N-phenylbenzamide as the final product.

Chemical Reaction:

 

Product Name: N-Phenylbenzamide (C₆H₅NHCOC₆H₅) .

13.8 Write structures of different isomers corresponding to the molecular formula, C3H9N. Write IUPAC names of the isomers which will liberate nitrogen gas on treatment with nitrous acid.

Answer: The molecular formula C₃H₉N represents amines and their isomers. The possible isomers include primary (1°), secondary (2°), and tertiary (3°) amines, as well as quaternary ammonium compounds.

Possible Isomers of C₃H₉N

1. Primary Amines (1° Amines)

   • Propan-1-amine (n-Propylamine) → CH₃CH₂CH₂NH₂
   • Propan-2-amine (Isopropylamine) → (CH₃)₂CHNH₂

2. Secondary Amines (2° Amines)

   • N-Methyl-ethanamine → CH₃CH₂NHCH₃
   • N-Ethyl-methanamine → CH₃NHCH₂CH₃

3. Tertiary Amine (3° Amine)

   • Trimethylamine → (CH₃)₃N

Isomers that Liberate Nitrogen Gas (N₂) with Nitrous Acid (HNO₂)

Only primary amines (1° amines) react with HNO₂ (nitrous acid) to form unstable diazonium salts, which decompose to alcohols and release nitrogen gas (N₂).

Reactions:

Thus, the isomers of C₃H₉N that liberate N₂ gas with HNO₂ are:

1. Propan-1-amine (n-Propylamine) → CH₃CH₂CH₂NH₂
2. Propan-2-amine (Isopropylamine) → (CH₃)₂CHNH₂

These are the only two isomers that will undergo this reaction.

13.9 Convert

(i) 3-Methylaniline into 3-nitrotoluene.

(ii) Aniline into 1,3,5 - tribromobenzene.

Answer : (i) React 3-Methylaniline with acetic anhydride (CH₃CO)₂O to form 3-Methylacetanilide (C₆H₄(CH₃)NHCOCH₃).

(ii)

(ii) React Aniline (C₆H₅NH₂) with sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at 0-5°C to form Benzenediazonium chloride (C₆H₅N₂⁺Cl⁻).

Class 12 Chemistry Chapter 13 Amines Exercise Questions and Answers :

Question 13.1 Write IUPAC names of the following compounds and classify them into primary,secondary and tertiary amines.

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

Answer : (i)

IUPAC name: Propan-2-amine

Classification: Primary amine (1°)

(ii) 

IUPAC name: Propan-1-amine

Classification: Primary amine (1°)

(iii)

IUPAC name: N-methylpropan-2-amine

Classification: Secondary amine (2°)

(iv) 

IUPAC name: 2-Methylpropan-2-amine

 Classification: Primary amine (1°)

(v) 

IUPAC name: N-methylbenzenamine or N-methylaniline  

Classification: Secondary amine (2°)

(vi) 

IUPAC name: N-ethyl-N-methylethanamine

Classification: Tertiary amine (3°)

(vii)

IUPAC name: 3-bromobenzeneamine or 3-bromoaniline

Classification: Primary amine (1°)

13.2 Give one chemical test to distinguish between the following pairs of compounds.

(i) Methylamine and dimethylamine (ii) Secondary and tertiary amines (iii) Ethylamine and aniline (iv) Aniline and benzylamine (v) Aniline and N-methylaniline.

Answer :

13.3 Account for the following:

(i)   of aniline is more than that of methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not.

(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

(iv) Although amino group is o- and p- directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.

(v) Aniline does not undergo Friedel-Crafts reaction.

(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines.

(vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.

Answer :

13.4 Arrange the following:

(i) In decreasing order of the pKb values:

 and

(ii) In increasing order of basic strength:

  and

(iii) In increasing order of basic strength:

(a) Aniline, p-nitroaniline and p-toluidine

(b) 

(iv) In decreasing order of basic strength in gas phase:

  and 

(v) In increasing order of boiling point:

 

(vi) In increasing order of solubility in water:

 

13.5 How will you convert:

(i) Ethanoic acid into methanamine

(ii) Hexanenitrile into 1-aminopentane

(iii) Methanol to ethanoic acid

(iv) Ethanamine into methanamine

(v) Ethanoic acid into propanoic acid

(vi) Methanamine into ethanamine

(vii) Nitromethane into dimethylamine

(viii) Propanoic acid into ethanoic acid?

13.6 Describe a method for the identification of primary, secondary and tertiary amines. Also write chemical equations of the reactions involved.

13.7 Write short notes on the following:

(i) Carbylamine reaction (ii) Diazotisation (iii) Hofmann’s bromamide reaction (iv) Coupling reaction (v) Ammonolysis (vi) Acetylation

(vii) Gabriel phthalimide synthesis.

13.8 Accomplish the following conversions:

(i) Nitrobenzene to benzoic acid

(ii) Benzene to m-bromophenol

(iii) Benzoic acid to aniline

(iv) Aniline to 2,4,6-tribromofluorobenzene

(v) Benzyl chloride to 2-phenylethanamine

(vi) Chlorobenzene to p-chloroaniline

(vii) Aniline to p-bromoaniline

(viii) Benzamide to toluene

(ix) Aniline to benzyl alcohol.

13.9 Give the structures of A, B and C in the following reactions:

Answer :  (i) 

 

 

A - Propanaitrile , B - Propanamide , C - Ethanamine .

(ii)  

A - Cyanobenzane , B - Benzoic acid , C - Benzamide

(iii)  

A - Cyanoethane , B - Propan-1-amine  , C - Propan-1-ol

(iv) 

A - Aniline or Benzenamine  , B - Benzenediazonium chloride , C - Phenol

(v) 

A - Ethanamide , B - Methaneamine , C - Methanol .

(vi)  

A - Aniline or Benzenamine , B - Benzenediazonium chloride , C - p-hydroxyaazobenzene .

13.10 An aromatic compound ‘A’ on treatment with aqueous ammonia and heating forms compound ‘B’ which on heating with and KOH forms a compound ‘C’ of molecular formula   . Write the structures and IUPAC names of compounds A, B and C.

13.11 Complete the following reactions:

13.12 Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?

13.13 Write the reactions of (i) aromatic and (ii) aliphatic primary amines with nitrous acid.

13.14 Give plausible explanation for each of the following:

(i) Why are amines less acidic than alcohols of comparable molecular masses?

(ii) Why do primary amines have higher boiling point than tertiary amines?

(iii) Why are aliphatic amines stronger bases than aromatic amines?