6.2.1 Amines

Question 1

Amines as bases

Answer 1

Act as Brønsted-Lowry bases because the lone pair of electrons on the N is readily available for forming a dative covalent bond with a H+ and so accepting a proton

Primary aliphatic amines are stronger bases than ammonia
- the alkyl groups are electron releasing and push electrons towards the nitrogen atom -> make it a stronger base

Primary aromatic amines do not form basic solutions
- the lone pair of electrons on the N delocalise with the ring of electrons in the benzene ring -> N is less able to accept protons

Question 2

Amines → Ammonium Salts

Answer 2

R-NH2 + HA → R-NH3+A-

Question 3

Forming 1° Amines

Answer 3

R-Br + 2NH3 → R-NH2 + NH4Br
Reagent: 1) Excess ammonia dissolved in ethanol
2) alkali e.g. NaOH (aq)
Mechanism: nucleophilic substitution

Question 4

Forming 2° Amines

Answer 4

R’-Br + 2R-NH2 → R-NH-R + R’-NH3+Br-
Reagent: 1) Excess primary amine dissolved in ethanol
2) alkali e.g. NaOH (aq)
Mechanism: nucleophilic substitution

Question 5

Nitroarenes → Aromatic amines

Answer 5

C6H5NO2 + 6[H] → C6H5NH2 + 2H2O
Reagents: 1) Sn and con. HCl 2) excess NaOH
Conditions: Reflux
Mechanism: reduction