3.3.11 - Amines

Question 1

Name the aliphatic amine and state the type of amine it is

Answer 1

Question 2

Name the aliphatic amine and state the type of amine it is

Answer 2

Question 3

Name the aliphatic amine and state the type of amine it is

Answer 3

Question 4

Name the aliphatic amine and state the type of amine it is

Answer 4

Question 5

Name the aromatic amine and state the type of amine it is

Answer 5

Question 6

Explain how a quaternary ammonium ion forms

Answer 6

Lone pair of electrons on nitrogen atom in tertiary amine can also bond with 4^th organic group

Question 7

Explain how quaternary ammonium salts form

Answer 7

Quaternary ammonium ions are positively charged ∴ form bonds around with -ve ions & form complexes (quaternary ammonium salts)

Question 8

What type of quaternary ammonium salts are used as cationic surfactants?

Answer 8

Quaternary ammonium salts with at least 1 long hydrocarbon chain

Question 9

What products are cationic surfactants used in?

Answer 9

Fabric cleaners (e.g. fabric conditioner) and hair products (e.g. conditioner)

Question 10

Describe and explain why cationic surfactants are useful in fabric cleaners and hair products

Answer 10

• Hydrocarbon tail binds to non-polar substances like grease & cationic head dissolves in water
• Positively charged part (ammonium ion) will bind to negatively charged surfaces e.g. hair and fibre
  
  • Gets rid of static

Question 11

Why do amines act as (weak) bases?

Answer 11

∵ accept protons

Question 12

Explain how amines can accept protons

Answer 12

Lone pair of electrons on nitrogen atom can form dative covalent (coordinate) bond with H⁺ ion

Question 13

What does the strength of a base depend on (for amines)?

Answer 13

Depends on how available nitrogen’s lone pair of electrons is

More available the lone pair is = more likely amine is to accept proton & stronger base it’ll be

Question 14

When is a lone pair of electrons more available?

Answer 14

When its electron density is high

Question 15

Order the amines from the weakest to strongest base

Ammonia, aliphatic amines, aromatic amines

Answer 15

1. Aromatic amines (weakest)
2. Ammonia
3. Aliphatic amines (strongest)

Question 16

Explain why primary aromatic amines (e.g. phenylamine) act as very weak bases

Answer 16

• Benzene ring draws electrons towards itself and nitrogen lone pair gets partially delocalised onto the ring
• ∴ the electron density on nitrogen ↓, making lone pair much less available

Question 17

Explain why primary aliphatic amines act as strong bases

Answer 17

• Alkyl groups push electrons onto attached groups
• ∴ electron density on nitrogen atom ↑
• Makes lone pair more available

Question 18

Why are amines considered nucleophiles?

Answer 18

∵ have lone pair of electrons

Question 19

Name the 2 mechanisms that amines partake in. Include the reactants.

Answer 19

• React with halogenoalkanes in nucleophilic substitution
• React with acyl chlorides and acid anhydrides in nucleophilic addition-elimination

Question 20

Name 2 ways you can make aliphatic amines

Answer 20

1. Heating halogenoalkane with excess ammonia
2. Reducing a nitrile (to a primary amine)

Question 21

Draw the mechanism to show how ethylamine can be made by reacting ammonia with bromoethane

Answer 21

Question 22

When heating halogenoalkane with ammonia, what mixture of products do you get?

Answer 22

Mixture of primary, secondary, tertiary amines + quaternary ammonium salts

Question 23

Explain how heating halogenoalkane with ammonia results in a mixture of primary, secondary, tertiary amines and quaternary ammonium salts

Answer 23

1. Primary amine 1st produced has lone pair of electrons = nucleophile
2. ∴ can react with any remaining halogenoalkane in nucleophilic substitution reaction
3. Further substitutions take place as long as there’s remaining halogenoalkane
4. Happens up to quaternary ammonium salt = can’t react further ∵ has no lone pair

Question 24

Write an equation for when a primary amine acts as a nucleophile with CH₂CH₂Br

Answer 24

Mechanism is similar to reaction of ammonia + halogenoalkane: 2 amine molecules react with halogenoalkane in succession to form more substituted amine (e.g. primary amine forms secondary amine) & ammonium salt with similar structure to original amine

Question 25

Describe 2 ways you can reduce a nitrile to a primary amine

Answer 25

1. Use lithium aluminium hydride (LiAlH₄ - strong reducing agent) in non-aqueous solvent e.g. dry ether followed by dilute acid
2. Catalytic hydrogenation: Reduced using hydrogen gas with metal catalyst e.g. platinum or nickel at high temperature and pressure

Question 26

Why is the LiAlH₄ method good in a lab but not good for industrial use?

Answer 26

LiAlH₄ is too expensive

(industry uses catalytic hydrogenation)

Question 27

Write an equation representing the reduction of a nitrile to a primary amine using lithium aluminium hydride

Answer 27

Question 28

Write an equation representing the reduction of a nitrile to a primary amine via catalytic hydrogenation

Answer 28

Question 29

State how you can produce aromatic amines

Answer 29

Reduce nitro compound e.g. nitrobenzene

Question 30

Describe how you can produce an aromatic amine by reducing nitro compound (e.g. nitrobenzene)

Answer 30

1. Heat mixture of nitro compound, tin metal & concentrated HCl under reflux
   
   • Makes salt
   • e.g. using nitrobenzene, salt formed = C₆H₅NH₃⁺Cl^-
2. To turn salt into aromatic amine, add alkali e.g. NaOH solution

Question 31

Write an equation representing the reduction of nitrobenzene into an aromatic amines

Answer 31

Question 32

Give an example of how aromatic amines are useful compounds in organic synthesis

Answer 32

Are starting molecules for lots of dyes and pharmaceuticals

Question 33

Amides are _______ ___ derivates

Answer 33

Amides are carboxylic acid derivates

Question 34

State the functional group of amides

Answer 34

-CONH₂

Question 35

Why do amides behave differently from amines?

Answer 35

Carbonyl group pulls electrons away from NH₂ group

Question 36

Draw an amide

Answer 36

Question 37

Draw an N-substituted amide

Answer 37

Question 38

Define the inductive effect

Answer 38

Ability of alkyl group to release electrons towards nitrogen atom

Question 39

Give the formula of an organic compound that forms an alkaline buffer solution when added to a solution of ethylamine

Answer 39

CH₃CH₂NH₃Cl

• (weak base + salt = alkaline buffer solution)
• (ethylamine + amine hydrochloride = alkaline buffer solution)
  
  • (add HCl to ethylamine to get salt)

Question 40

Name the following compound

Answer 40

Question 41

Name the following compound

Answer 41

N-ethylpropanamide

Question 42

Write an ionic equation for the reaction between propylamine and hydrochloric acid

Answer 42

CH₃CH₂CH₂NH₂ + H⁺ → CH₃CH₂CH₂NH₃⁺

(original equation: CH₃CH₂CH₂NH₂ + HCl → CH₃CH₂CH₂NH₃Cl)

Question 43

Propylamine reacts with bromoethane under specific conditions, to give a compound with the formula C₉H₂₂NBr. Draw the structure of the compound with the formula C₉H₂₂NBr.

Answer 43