Amines

Question 1

Are aromatic amines basic?

Answer 1

• No!
• Eg: phenyl amine - don’t form basic solutions because the lone electrons pair on the nitrogen is delocalised into the ring.
• Makes nitrogen less able to accept protons.

Question 2

Amines can react with acids.

Answer 2

• As amines are basic, they can react with acids to form salt.
• Eg: CH3NH2 + HCl –> CH3NH3+Cl-.
• Addition of NaOH to a salt will convert it back to an anime.

Question 3

How can aliphatic amines be formed?

Answer 3

• By the reaction between a halogenoalkane and excess ethanolic ammonia.
• Occurs by nucleophilic substitution.

•E.g: CH3CH2Br + 2 NH3 –> CH3CH2NH2 + NH4Br.

Question 4

Why is excess ammonia necessary for the formation of aliphatic amines?

Answer 4

•Limits further substitution reactions & maximise the amount of primary amines formed.

Question 5

How can aromatic amines be formed?

Answer 5

• By the reduction of nitrobenzene.
• Conditions: Sn and conc HCl; reflux. This makes a salt : C6H5NH3+Cl- .
• In order to get the aromatic amine, add NaOH.

Eq: C6H5NO2 + 6[H]–> C6H5NH2+ 2H2O

Question 6

Describe the synthesis of azo dyes.

Answer 6

Step 1) React phenyl amine with nitrous acid to form a diazonium salt.
•Nitrous acid is unstable, so it’s made in situ from sodium nitrite + HCl.
NaNO2 + HCl–> HNO2 + NaCl.

Step 2) Coupling of the diazonium ion and phenol to produce the azo dye.
•Alkaline conditions (NaOH).

Question 7

Uses of azo dyes?

Answer 7

• Food colouring
• Produce paint pigments
• Dyes

Question 8

What are properties of amines?

Answer 8

•Amines are basic, due to the lone electron pair on the nitrogen accepts a H+ ion to form a dative covalent bond.

E.g: NH3 + H+ —> NH4+.