Amines

Question 1

How are secondary amines named?

Answer 1

N- prefix used before the shorter alkyl chain, longest chain named as primary amine

Question 2

How are tertiary amines named?

Answer 2

2 N- prefixes used before 2 shorter alkyl chains. Longest chain named as primary amine

Question 3

Why is CH3NH2 a stronger base than ammonia?

Answer 3

CH3NH2 has alkyl groups, which are electron donating, hence the positive inductive effect is present, hence this effect pushes electrons to N. The electron density on the nitrogen atom increases, making the lone pair on the nitrogen more available to accept a proton.

Question 4

Why are aromatic amines weaker bases than ammonia?

Answer 4

The benzene ring draws electrons towards itself and the nitrogen’s lone pair get delocalised into the ring. Therefore, the lone pair on the N is less available to accept a proton.

Question 5

How do you prepare primary amines from ammonia and halogenoalkanes?

Answer 5

Reagent: ammonia dissolved in ethanol
Condition: Excess ammonia + heat under pressure
Product: Amine
Nucleophile: NH3

Question 6

Why is the ammonia dissolved in ethanol in the preparation of primary amines?

Answer 6

The halogenoalkane is soluble in ethanol

Question 7

What is the equation for preparing primary amines from ammonia and halogenoalkanes?

Answer 7

C2H5Br + 2NH3 –> C2H5NH2 +NH4Br

Question 8

Why is excess ammonia used in production of primary amines (with halogenoalkanes)?

Answer 8

Increase yield of primary amines by minimising further substitution or reducing the formation of secondary/ tertiary amines.

Question 9

What are the disadvantages of using halogenoalkanes and ammonia to make primary amines?

Answer 9

There can be further reaction of primary amines
Impure product/ mixture of products/ lower atom economy

Question 10

What is a quaternary ammonium salt?

Answer 10

An ammonium salt in which all the hydrogens have been replaced by an alkyl group e.g. (CH3CH2)4N+Br-

Question 11

What are the uses of quaternary ammonium salts?

Answer 11

Cationic surfactants (reduce the surface tension of liquids).
Fabric softeners and hair conditioners

Question 12

How do you prepare primary amines by the reduction of nitriles?

Answer 12

Step 1: convert halogenoalkane to nitrile
Reagent: KCN or NaCN (not HCN)
Condition: aqueous ethanol
Step 2: reduce nitrile to amine
Reagent: H2
Condition: Ni/Pt catalyst

Question 13

What is the equation for reducing nitriles to form primary amines?

Answer 13

CH3CH2CN + 4[H] -> CH3CH2CH2NH2

Question 14

What are the advantages of using nitriles to make primary amines?

Answer 14

No further reaction
Single product/ higher atom economy

Question 15

What is the disadvantage of using nitriles to make primary amines?

Answer 15

KCN is toxic

Question 16

How can aromatic amines be prepared?

Answer 16

Reduction of benzene

Question 17

How can primary amines be prepared?

Answer 17

React ammonia with halogenoalkanes
Reduce nitriles

Question 18

How can you prepare an amine through reduction of benzene?

Answer 18

Reagent: Sn with concentrated HCl
Condition: Heating
Reaction type: Reduction

Question 19

In the preparation of aromatic amines, why is an aqueous solution obtained?

Answer 19

Phenylamine is insoluble in water, however, under acidic conditions, it exists as phenylammonium ions, which is a salt (?) and is soluble. (the lone pair on the nitrogen in phenylamine picks up a hydrogen ion from the acid)

Question 20

What are the uses of aromatic amines?

Answer 20

Dyes