Question

Mutliple step synthesis for 4-bromoacetanilide from aniline

1. during the synthesis of aniline from nitrobenxe, explain why it was necessary to make the solution alkaline (addition of NaOH)

2. During filtration, why is it important to only wash the solid with ice-cold solvent?

3. Why is it necessary ti acylate aniline prior to bromination?

4. If the synthesis of p-bromoacetanilide also provided a small amount of o-bromoacetanilide after the crystallixation step, how would that influence the melting point range od p-bromoacetanilide?

Answer 1

1 First nitro benzene is converted to phenylammoniun ion. This is formed in acidic condition

To convert phenylammoniun ion to phenylamine base is added

The base will remove the hydrogen from positively charged phenylammoniun ion

2 The solute is not soluble in ice cold solvent

So it is safe to use this solvent

It helps to rinse the impurities off the crystal surface

3 if the aniline is not acyletated the tri substituted product will be formed. The amino group is strongly activating

The acylated amino group is less activating because there is delocalisation of electrons within the group itself and competes with delocalisation into the ring.

The second reason is that the steric bulkiness of the acetanilide also interferes with the formation of the ortho product.

Once brominated, the amino group can be regenerated by treatment with either acid or base.

4 it affects the melting point range

Due to the impurity present in crystals