Amines and their reactions 38-39

Question 1

How can aliphatic amines be prepared?

Answer 1

Aliphatic amines can be prepared by warming halogenoalkanes gently with an excess of ammonia, using ethanol as a solvent.

Question 2

What type of reaction is that of preapring aliphatic amines?

Answer 2

Nucleophilic substitution

Question 3

Write out the reaction for the preparation of propylamine.

Answer 3

CH₃CH₂CH₂Cl + NH₃ → CH₃CH₂CH₂NH₂ + HCl

Further ammonia can then reat with the hydrogen chloride formed.

NH₃ + HCl → NH₄⁺Cl^-

Question 4

Explain why the preparation of aliphatic ammines the ammonia is in excess.

Answer 4

The product from the reaction has a nitrogen which has a lone pair of electrons which then allows it to attack the reactants ( the chloroalkanes).

CH₃Cl + NH₃ → CH₃NH₂ + HCl

then

CH₃Cl + CH₃NH₂ → (CH₃)₂NH + HCl

The excess ammonia means theres less chance of the primary amine product to react further.

Question 5

How can aromatic amines be prepared?

Answer 5

Nitrobenzene and other nitroarenes can be reduced using a mixture of tin and concentrated hydrochloric acid, heated under reflux, followed by neutralisation of the excess hydrochloric acid. Aromatic amines are formed as products in these reactions.

Question 6

Write out the reaction for the reduction of nitrobenzene to make pheylamine.

Answer 6

Question 7

What are the two steps in the industrial preparation of dyestuffs?

Answer 7

• Diazotisation
• Coupling reactions

Question 8

Explain the reaction conditions and reagents for diazotisation.

(Explain how HNO₂) is made

Answer 8

When a mixture of phenylamine and nitrous acid is kept below 10*C a diazonium salt is formed.

Nitrous acid, HNO₂, is generated in the reaction mixture by reacting together sodium nitrate, NaNO₂, and excess hydrochloric acid, HCl:

NaNO₂ + HCl → HNO₂ + NaCl

The cold nitrous acid then reacts with an aromatic amine to form a diazonium salt.

Question 9

Give the reaction for the diazotisation of phenylamine.

Answer 9

Question 10

Describe the reaction called coupling.

Answer 10

A coupling reaction occurs when the diazonium salt, benzenediazonium chloride, is reacted with a phenol. (or other aromatic compound, such as an amine) under alkaline conditions. In this reaction, two benzene rings are linked together through an azo function group, -N=N-.

Question 11

Write out the coupling reaction of phenol with benzendiazonium chloride.

Answer 11