Chapter 28 (Amines)

Question 1

Why do primary aliphatic amine act as bases?

Answer 1

The lone pair on the nitrogen is readily available to form a covalent bond with a H+ so accepts a proton.

Question 2

Why are primary aliphatic amines weak bases?

Answer 2

Only a low concentration of hydroxide ions is produced.

Question 3

Why are primary aliphatic amines stronger bases than ammonia?

Answer 3

The alkyl groups are electron releasing and push electrons towards the nitrogen atom and make it a stronger base.

Question 4

Why are secondary amines stronger bases than primary amines?

Answer 4

They have more alkyl groups that are substituted onto the N atom in place of H atoms. Therefore the electron density is pushed onto the N atom.

Question 5

Why are tertiary amines weaker bases than secondary amines?

Answer 5

Tertiary amines are less soluble in water.

Question 6

Why are aromatic amines weaker bases than aliphatic?

Answer 6

The lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring so the N is less able to accept protons.

Question 7

Equation between methyl amine and proton

Answer 7

CH3NH2 (aq) + H+ (aq) > CH3NH3+(aq)

Question 8

Example of equation between secondary amine and proton

Answer 8

(CH3CH2)2 NH (aq) + H+ (aq) > (CH3CH2)2NH2+(aq)

Question 9

Example of equation between tertiary amine and proton

Answer 9

(CH3CH2)3 N (aq) + H+ (aq) > (CH3CH2)3NH+(aq)

Question 10

What is reacted with an amine to form an ammonium salt?

Answer 10

A base

Question 11

What is added to an ammonium salt to convert it back to an amine?

Answer 11

NaOH

Question 12

How do ammonium salts appear?

Answer 12

Ionic crystals after water has been evaporated due to strong ionic interactions

Question 13

How is a buffer formed from an amine?

Answer 13

Combing a weak base with a salt of that base

Question 14

What mechanism forms primary amines?

Answer 14

Nucleophilic Substitution

Question 15

Why is nucleophilic substitution not a good way to form primary amines?

Answer 15

The lone pair on the N can react in a successive of reactions to form other amines and ammonium salts. This means that the desired product would need to be separated from the other products.

Question 16

What is the initial nucleophile in the mechanism to form primary amines?

Answer 16

Ammonia dissolved in ethanol

Question 17

How can the yield of primary amines be increased?

Answer 17

Use excess ammonia which limits subsequent reactions.

Question 18

How is a secondary amine formed from a primary amine?

Answer 18

The lone pair of electrons on the N will react with a haloalkane.

Question 19

How is the yield of ammonium salts increased?

Answer 19

Excess of haloalkanes

Question 20

What can ammonium salts be used for and what is their purpose?

Answer 20

Cationic surfactants

Reduce the surface tension of liquids as the positive nitrogen is attracted towards a negatively charged surface.

Question 21

Describe the method for preparing amines from nitriles

Answer 21

1) Convert haloalkane to nitrile using KCN in ethanol

2) Reduce nitrile to amine using LiAlH4 or by reducing with H2 and Ni catalyst.

Question 22

Whats are the reagents, conditions and mechanism for reducing a nitroamine to an aromatic amine?

Answer 22

Reagent: Sn and HCl or Fe and HCl

Condition: Heat

Mechanism: Reduction

Question 23

What is the disadvantage of using a haloalkane first to produce an amine from a nitrile?

Answer 23

• Two step reaction so may have a lower yield

* Uses KCN which is toxic

Question 24

What is the reagent and condition for changing functional group from acyl chloride/acid anhydride to secondary amide and what type of mechanism?

Answer 24

Reagent: Primary amine

Conditions: Room Temperature

Mechanism: Nucleophilic addition-elimiantion

Question 25

What is a use of aromatic amines?

Answer 25

Dye making as cause colour change and ability of dyes to bond to fabric

Question 26

Why do the methods for making aliphatic amines not work for aromatic amines?

Answer 26

• Benzene rings repels nucleophile due to delocalised electrons. N in ammonia is nucleophilic.
• Aromatic ring is e- attracting so lone pairs of halogens are pulled towards the ring. Shortens the C-X bond making it less reactive.

Question 27

Why are two moles of ammonia used when reacting with acyl chloride/acid anhydride?

Answer 27

First acts as a nucleophile and seconds acts as a base (deprotonates the amine group)

Question 28

Give order of base strength weakest to strongest

Answer 28

Aromatic < Ammonia < Primary < Tertiary < Secondary