Amines (Organic) (complete)

Question 1

How are amines formed using ammonia?

Answer 1

• Addition of ammonia to a halogenoalkane. The ammonia is dissolved in ethanol, and is substituted onto the halogenoalkane at pressure in a sealed container.
• Further substitutions occur between the 1˚ amine and halogenoalkane to produce 2˚ and then 3˚ amines and 4˚ ammonium salts.

Question 2

How can you ensure mostly 1˚ amine is formed during the substitution of ammonia onto halogenoalkanes to formed amines?

Answer 2

• Add excess ammonia to ensure no further substitutions occur forming 2˚ and 3˚ amines.

Question 3

Name the two ways of producing aliphatic amines.

Answer 3

• Substitution of ammonia onto halogenoalkanes
• Reduction of nitrile compounds.

Question 4

Describe how to make amines by reduction of nitrile compounds.

Answer 4

1 - Formation of nitrile from halogenoalkane - warm ethanol catalyst
2 - Reduction of nitrile to form amine - LiAlH4 in ethoxyethane — or — Ni catalyst and heated

Question 5

How are aromatic amines prepared?

Answer 5

• Reduction of nitro compounds using tin and conc HCl, followed by NaOH.

Question 6

How can the base strength of amines be determined?

Answer 6

The higher the electron density of the N atom lone pair, the stronger the base as it can accept protons better.

Question 7

What is the order of base strength between:
1˚amines, 2˚amines, 3˚amines, ammonia and aromatic amines?
Why?

Answer 7

3˚ amines > 2˚ amines > 1˚ amines > ammonia > aromatic amines

Compared to ammonia, the more alkyl groups that are substituted onto the N atom in place of H atoms, the more the electron density is pushed onto the N atom, so better base.
Compared to ammonia, the N atom on the aromatic amine is partially delocalised into the benzene ring, leading to reduction in electron density, therefore worse base.