6.2.1 Amines

Question 1

What is the basicity of amines explained in terms of proton acceptance?

Answer 1

Amines act as bases because the nitrogen lone pair can accept a proton (H+), forming a dative covalent bond.

Question 2

What is formed when amines react with dilute acids like HCl(aq)?

Answer 2

Amines react with dilute acids to form ammonium salts, e.g., RNH2 + HCl → RNH3+Cl-.

Question 3

How are aliphatic amines prepared from haloalkanes?

Answer 3

By nucleophilic substitution: excess ethanolic ammonia reacts with a haloalkane, replacing the halogen with an amine group.

Question 4

What is the general reaction for the preparation of primary aliphatic amines?

Answer 4

RX + 2NH3 → RNH2 + NH4X (where RX is a haloalkane).

Question 5

How are secondary and tertiary amines formed from primary amines?

Answer 5

Further substitution occurs: primary amines react with more haloalkane to form secondary amines, and secondary amines react to form tertiary amines.

Question 6

What reagents and conditions are used to reduce nitroarenes to aromatic amines?

Answer 6

Tin (Sn) and concentrated hydrochloric acid (HCl) under reflux, followed by neutralisation with sodium hydroxide (NaOH).

Question 7

What is the equation for the reduction of nitrobenzene to phenylamine?

Answer 7

C6H5NO2 + 6[H] → C6H5NH2 + 2H2O (using Sn and conc. HCl, then NaOH).

Question 8

What alternative method can be used to form amines?

Answer 8

Reduction of nitriles using LiAlH4 in dry ether or catalytic hydrogenation with H2/Ni catalyst.