Amines

Question 1

Describe the structure of an amine.

Answer 1

Derived from ammonia molecules and all contain a nitrogen atom where hydrogens are replaced with an organic group e.g. an alkyl group.

Question 2

Describe the structure of a primary amine.

Answer 2

One alkyl group replaces hydrogen.
2 hydrogens and 1 alkyl group

Question 3

Describe the structure of secondary amines.

Answer 3

2 alkyl groups replace hydrogens;
2 alkyl groups and 1 hydrogen.

Question 4

Describe the structure of tertiary amines.

Answer 4

Three alkyl groups replace the three hydrogens.

Question 5

Describe the structure of a quaternary ion.

Answer 5

4 alkyl groups surround the nitrogen therefore it has a positive charge.

Question 6

How can primary aliphatic amines be prepared?

Answer 6

By the reaction of ammonia (NH3) with halogenoalkanes
AND
The reduction of nitriles.

Question 7

What is an aromatic amine?

Answer 7

A primary amine.

Question 8

What is a cationic surfactant?

Answer 8

Quaternary ammonia salts that have a long hydrocarbon ‘tail’;
Quaternary salts are made from a positive head group and is attracted to negative ions.

Question 9

State some of the uses of cationic surfactants.

Answer 9

Used to make cleaning products such as shampoo, laundry detergents and washing up liquids.

Question 10

How do cationic surfactants work?

Answer 10

The non-polar tail is attracted to the oil/grease;
The polar head will be attracted to the water;
This allows the water and oil to mix and removes grease from clothing, skin and dishes.

Question 11

How can amines act as bases?

Answer 11

Amines have a lone pair of electrons that allows them to accept a proton.

Question 12

How does the proton bind to the amine?

Answer 12

Via a dative covalent bond;
Both electrons in the bond originate from the lone pair on the nitrogen.

Question 13

What is the strength of the base dependent on?

Answer 13

The availability of the lone pair of electrons on the nitrogen;
The higher the electron density the more readily available the electrons are.

Question 14

What is electron density on the nitrogen dependent on?

Answer 14

The type of group attached to the nitrogen.

Question 15

State the order of base strength from weakest to strongest.

Answer 15

Aromatic amines> ammonia > primary aliphatic amines

Question 16

Explain why benzene is the weakest base.

Answer 16

Benzene is an electron withdrawing group so it pulls electrons away from the nitrogen into the ring structure;
Electron density at nitrogen reduces so the lone pair availability is reduced and aromatic amines are less basic.

Question 17

Explain why primary aliphatic amines are the strongest base.

Answer 17

Alkyl groups are electron pushing groups so they push electrons towards nitrogen;
Electron density at nitrogen increases so lone pair availability increases and primary aliphatic amines are more basic.

Question 18

State another property on amines other than as bases.

Answer 18

They are nucleophiles.

Question 19

State the mechanism when reacting halogenoalkane and ammonia.
State the reagents and conditions.

Answer 19

Mechanism: Nucleophilic substitution
Reagent: Ammonia in EXCESS
Conditions: Heat

Question 20

Draw the mechanism when chloroethane reacts with excess ammonia.

Answer 20

1. First curly arrow from lone pair on ammonia to delta positive carbon.
2. Second curly around from C-CL bond to delta negative chlorine.
   EXCESS AMMONIA SO:
3. Third curly arrow from lone pair on ammonia to H on positive N
4. Fourth curly arrow from N-H bond to positive N.

Question 21

What is the downside of reacting halogenoalkanes and ammonia?

Answer 21

The reaction also produces secondary, tertiary and quaternary salts so we have an impure product;
This occurs as primary amine still have a lone pair of electrons on the nitrogen so also act as a nucleophile;
The amine can react with any remaining halogenoalkane to produce secondary amines, then react further to make tertiary and quaternary salts.

Question 22

State the reagents and conditions when reducing nitriles to produce amines.

Answer 22

Reagent - H2 (hydrogen gas)
Conditions - Ni (nickel catalyst), hight temp and pressure.

Reagent - LiAlH4 (strong reducing reagent) and dilute acid

Question 23

What is the reaction of reducing nitriles called when using H2 gas and a nickel catalyst?

Answer 23

Catalytic Hydrogenation

Question 24

What are advantages of producing amines from reducing nitriles using hydrogen gas and nickel catalyst?

Answer 24

1. Cheapest way to make primary amines in industry.
2. Only produces primary amines so a pure product is made.

Question 25

What is the reaction called when we use LiAlH4 and dilute acid to reduce nitriles?

Answer 25

Reduction reaction

Question 26

What are disadvantages of the reduction reaction?

Answer 26

More expensive than catalytic hydrogenation and LiAlH4 is more expensive than H2 gas and a nickel catalyst so it is not used in industry.

Question 27

What is the reducing agent in the reduction reaction to make amines from nitriles dissolved in?

Answer 27

A non-aqueous solvent such as dry ether.

Question 28

How are aromatic amines produced?

Answer 28

Made by reducing nitrocompounds such as nitrobenzene.

Question 29

What are aromatic amines used for?

Answer 29

To make dyes and pharmaceuticals.

Question 30

Describe the steps to make aromatic amines from nitrobenzene.

Answer 30

Step 1 - heat nitrobenzene under reflux with concentrated HCL and tin to form a salt.
Step 2 - The salt produced is reacted with an alkali such as NaOH to produce an aromatic amine.