Amines

Question 1

What are amines?

Answer 1

Amines are organic derivatives of ammonia

Question 2

What is the functional group of amines?

Answer 2

NR2, where R is a hydrogen or an alkyl group

Question 3

If the nitrogen atom is bonded to 4 alkyl groups, what do you get?

Answer 3

A positively charged quaternary ion

Question 4

How do you make an aliphatic amine from a halogenoalkane?

Answer 4

Heat a halogenoalkane with an excess of ethanolic ammonia

Question 5

What is the problem with forming an amine from a halogenoalkane?

Answer 5

You get a mixture of primary, secondary and tertiary amines

Question 6

Why are a mixture of products formed when you heat a halogenoalkane with excess ethanolic ammonia?

Answer 6

The nitrogen atom in the amine has a lone pair of electrons making it a nucleophile, meaning it can take part in further substitution reactions

Question 7

What is the first way of reducing a nitrile to a primary amine?

Answer 7

Reduce using lithium aluminium hydride (LiAlH4) followed by some dilute acid

Question 8

What is the problem with reducing a nitrile to form an amine using lithium aluminium hydride?

Answer 8

LiAlH4 is far too expensive for industrial use

Question 9

As LiAlH4 is far too expensive for industrial use, what is the second way of reducing a nitrile to an amine?

Answer 9

Reduce using hydrogen gas and a metal catalyst (e.g. nickel) at a high temp and pressure, which is called catalytic hydrogenation

Question 10

How do you form an aromatic amine from a nitrobenzene?

Answer 10

• Heat nitrobenzene with tin metal and conc HCl under reflux, which creates a salt
• Then add sodium hydroxide to form phenylamine

Question 11

Why are amines able to act as weak bases?

Answer 11

Because they accept protons, due to the lone pair of electrons on the nitrogen, that can form a dative covalent bond with a H+ ion

Question 12

What does the strength of the amine base depend on?

Answer 12

How available the nitrogen’s lone pair of electrons are, the more available, the stronger the base

Question 13

List in order of strength of base: Aromatic amines, primary aliphatic amines, ammonia

Answer 13

Primary aliphatic amine
Ammonia
Primary aromatic amine

Question 14

Why are primary aromatic amines the weakest type of base?

Answer 14

The benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring, so the electron density on the nitrogen decreases, making the lone pair much less available

Question 15

Why are primary aliphatic amines the strongest base?

Answer 15

Alkyl groups push electrons onto the attached groups, so the electron density on the nitrogen atom increases, making the lone pair more available

Question 16

Why are amines nucleophilles?

Answer 16

Due to the lone pair of electrons on the nitrogen atom

Question 17

What happens when amines are neutralised by acids?

Answer 17

They form ammonium salts (e.g. CH3CH2NH3+CL-

Question 18

Why are small amines soluble in water?

Answer 18

The amine group can form hydrogen bonds with the water molecules

Question 19

Why are larger amines not soluble in water?

Answer 19

The bigger the amine, the greater the London forces between the amine molecules and the more energy it takes to break them apart. Also larger carbon chains disrupt the hydrogen bonding in water, but can’t form hydrogen bonds themselves, so large amines are less soluble than smaller ones

Question 20

When amines dissolve in water, what do they form?

Answer 20

They form alkaline solutions

Question 21

What happens in copper (II) sulfate solution?

Answer 21

The Cu2+ ions form complexes with the water, forming a blue solution

Question 22

What happens if you add a small amount of butylamine to copper(II) sulfate

Answer 22

You will get a pale blue precipitate, as the amine acts as a base and takes 2 H+ from the complex, forming a pale blue precipitate of copper hydroxide, which is insoluble

Question 23

What happens when you add butylamine in excess to copper sulfate solution?

Answer 23

The precipitate dissolves to form a deep blue solution as a complex ion is formed

Question 24

How do you form a secondary amine from a primary amine?

Answer 24

React with halogenoalkane, and react again to form a tertiary amine

Question 25

What happens when an amine reacts with an acyl chloride?

Answer 25

An N-substituted amide is formed alongside HCl.

Question 26

What happens when an amine reacts with HCl?

Answer 26

It forms a salt, which is solid white

Question 27

What is an the functional group of an amide?

Answer 27

CONH2

Question 28

What is an N-subsituted amide?

Answer 28

When one of the hydrogen atoms is replaced with an alkyl group

Question 29

What is the suffix of amides?

Answer 29

-amide

Question 30

How do you form a primary amide?

Answer 30

React ethanoyl chloride with ammonia

Question 31

How do you form an N-substituted amide?

Answer 31

React ethanoyl chloride with a primary amine