3.11 Amines

Question 1

Amines

Answer 1

Compounds based on ammonia with at least one hydrogen atom replaced by an alkyl or aryl group

Question 2

How are amines classified?

Answer 2

By the number of R groups bonded to nitrogen

Question 3

General formula for aliphatic amines

Answer 3

CₙH₂ₙ₊₃N

Question 4

How are primary aliphatic amines produced?

Answer 4

• Nucleophilic substitution of halogenoalkanes with ammonia
• Reduction of nitriles

Question 5

Reagents and conditions for the reduction of nitriles to primary amines

Answer 5

• Hydrogen
• Nickel (catalyst)
• High temperature and pressure

Question 6

Equation for the reduction of nitriles to primary amines

Answer 6

R-C≡N + 2H₂ –> RCH₂NH₂

Question 7

Reagents and conditions for the preparation of primary aliphatic amines from halogenoalkanes

Answer 7

• Excess ammonia (prevents further substitution)
• Ethanol as a solvent

Question 8

Why are ammonia and amines weak bases?

Answer 8

The lone pair on nitrogen can accept a proton from an acid

Question 9

Product of the reaction between amines and acids

Answer 9

Alkylammonium salts

Question 10

Basicity

Answer 10

The ability of a substance to act as a base

Question 11

Amines in order of increasing basicity

Answer 11

• Aromatic
• Ammonia
• Primary aliphatic amines

Question 12

Why are primary amines stronger bases than ammonia?

Answer 12

• Alkyl group releases electron density towards N (positive inductive effect)
• Increases electron density around N
• Lone pair is more available to accept H⁺

Question 13

Why are aromatic amines weaker bases than ammonia?

Answer 13

• Lone pair on N is delocalised into the pi-ring
• Decreases electron density on N
• Lone pair is less available to accept H⁺

Question 14

Product when further nucleophilic substitution occurs with halogenoalkanes and ammonia?

Answer 14

Quaternary ammonium salts (or secondary/tertiary amines if reaction is stopped before this point)

Question 15

Nucleophilic substitution of halogenoalkanes with excess ammonia/amine

Answer 15

Only one alkyl group is added to the amine/ammonia

Question 16

Nucleophilic substitution of halogenoalkanes with excess halogenoalkane

Answer 16

More than one alkyl group is added (forms quaternary ammonium salts)

Question 17

Use of quaternary ammonium salts

Answer 17

Cationic surfactants (used in detergents and fabric softeners)

Question 18

Surfactants

Answer 18

Compounds with regions that are partly soluble and partly insoluble in water

Question 19

Why do quaternary ammonium salts act as surfactants?

Answer 19

• The ionic region is soluble in water
• The long non-polar hydrocarbon chains are insoluble