Amines

Question 1

What are amines?

Answer 1

Deratives of ammonia in which one or more hydrogen is replaced by alkyl or aryl group

Question 2

What is a primary amine?

Answer 2

Amines in which only one hydrogen atom in ammonia molecule has been replaced

Question 3

What is a secondary amine?

Answer 3

Amines in which two hydrogen atoms in ammonia molecule have been replaced

Question 4

What is a tertiary amine?

Answer 4

Amines in which three hydrogen atoms in ammonia molecule have been replaced

Question 5

What is an aliphatic amine?

Answer 5

Amine in which R group is alkyl group

Question 6

What is an aromatic amine?

Answer 6

Amine in which R group is aryl group

Question 7

What two reactions can be used to prepare primary amines?

Answer 7

Reaction of halogenoalkanes with ammonia
Reduction of nitriles

Question 8

What is the reaction of halogenoalkanes with ammonia?

Answer 8

A nucleophilic substitution reaction in which nitrogen lone pair in ammonia acts as nucleophile and replaces halogen in halogenoalkane

Question 9

How is primary amine formed from halogenoalkane?

Answer 9

Reacted with excess, hot ethanolic ammonia under pressure

Question 10

What happens during the reduction of nitriles?

Answer 10

Nitrile vapor and hydrogen gas pass over nickel catalyst or LiAlH₄ in dry ether

Question 11

What reduction is made in terms of functional groups in nitriles?

Answer 11

-CN reduced to -NH₂

Question 12

What is phenylamine?

Answer 12

Organic compounds consisting of benzene ring and amine functional group

Question 13

Describe the synthesis of phenylamine.

Answer 13

Benzene undergoes nitration with conc nitric acid and conc sulfuric acid at 25-60ᵒC to form nitrobenzene
Nitrobenzene reduced with hot tin and conc hydrochloric acid under reflux to form acidic mixture containing organic product
Sodium hydroxide added to acidic reaction mixture to form phenylamine
Phenylamine separated from reaction mixture by steam distillation

Question 14

Is the nitrogen atom in ammonia and amine molecules a proton donor or acceptor?

Answer 14

Proton acceptor

Question 15

How do ammonia and amine molecules act in aqueous solutions?

Answer 15

As bases by donating lone pair of electrons to proton to form dative bond

Question 16

Are ammonium/amine salts soluble?

Answer 16

Soluble ionic compounds
Small alkyl groups means soluble in water
Less so as carbon chain increases

Question 17

What determines the strength of an amine?

Answer 17

The ability of lone pair on nitrogen to accept proton and form dative covalent bond
More readily proton attracts, stronger the base

Question 18

What factors affect the basicity of amines?

Answer 18

Positive inductive effect
Delocalisation

Question 19

How does the positive inductive effect affect basicity of amines?

Answer 19

Some groups donate electron density to nitrogen atom so lone pair more available and basicity increases

Question 20

How does delocalisation affect basicity of amines?

Answer 20

Presence of aromatic rings e.g. benzene causes lone pair of electrons on nitrogen to be delocalised into ring
Lone pair less available to form dative covalent bond with ammonia and so basicity decreases

Question 21

Why are amines good nucleophiles?

Answer 21

Lone pair on nitrogen atom

Question 22

How does ammonia form primary amine?

Answer 22

Ammonia reacts with haloalkane in nucleophilic substitution reaction

Question 23

How does ammonia act in first step of nucleophilic substitution with halogenoalkane?

Answer 23

As nucleophile

Question 24

How does ammonia act in second step of nucleophilic substitution with halogenoalkane?

Answer 24

As base

Question 25

What reactions do amines/ammonia undergo with acyl chlorides and acid anhydrides?

Answer 25

Nucleophilic substitution (also called nucleophilic addition-elimination)

Question 26

How do amines/ammonia undergo nucleophilic addition-elimination with acyl chlorides and acid anhydrides?

Answer 26

Delta positive carbon is site of nucleophilic attack by lone pair on nitrogen Chlorine more electronegative than oxygen so stronger dipole created along C-Cl so carbon prone to nucleophilic attack HCl produced as elimination product which reacts to form ammonium chloride

Question 27

What is produced in reaction between acyl chlorides and ammonia?

Answer 27

Non-substituted amide and white fumes of NH₄Cl

Question 28

What is produced in reaction between acyl chlorides and amines?

Answer 28

Substituted amide and HCl formed reacts with unreacted amine to form white organic ammonium salt

Question 29

What differs between acyl chloride reactions with ammonia and amines?

Answer 29

Both vigorous - different products

Question 30

What are quaternary ammonium salts?

Answer 30

Chemical analogues to ammonium chloride in which all four hydrogens have been replaced by alkyl groups

Question 31

What are surfactants?

Answer 31

Chemicals that lower surface tension between immiscible liquids and allow wetting to take place

Question 32

Why are quarternary ammonium salts cationic surfactants?

Answer 32

Due to positive charge on nitrogen

Question 33

Why are quarternary ammonium salts surfactants?

Answer 33

Hydrocarbon groups hydrophobic and amine group hydrophilic Allows molecules to cluster on surface of water with hydrophilic charged ends in water and hydrophobic tails on surface

Question 34

How does hair conditioner work?

Answer 34

Attracted to wet surfaces due to positive charge on surfactant Forms coating on hair to prevent build up of static