Question

How will you convert the following?
1.Nitrobenzene into aniline
2.Ethanoic acid into methanamine
3.Aniline into N-phenylethanamide
(Write the chemical equations involved).

Answer 1

Hint: Aliphatic and aromatic primary amines can both be easily prepared by the reduction of the corresponding nitro compounds.
Carboxylic acids can be converted first to the corresponding amides which will then give an amine having one carbon atom by Hofmann bromamide reaction.
Acylation of aromatic compounds is usually carried out in the presence of a catalyst. Acylation is the process of introducing an acyl group $\left( {{\text{RCO - }}} \right)$ into any molecule.

Complete step by step answer:
i. Nitrobenzene is an aromatic nitro compound and aniline is its corresponding aromatic primary amine. So, nitrobenzene can be converted into aniline by reduction with an active metal like iron, tin, zinc etc. and concentrated hydrochloric acid.

ii. Ethanoic acid is first converted into ethanamide by the action of ${\text{SOC}}{{\text{l}}_{\text{2}}}$ and then by Hofmann bromamide reaction, ethanamide is converted into methanamine.

iii. Primary and secondary amines have one hydrogen atom and two hydrogen atoms respectively on the nitrogen atom. So, they can undergo nucleophilic acylation reactions when treated with acid chlorides, acid anhydrides or esters to form N- substituted amides. Tertiary amines do not have any hydrogen atom on the nitrogen atom and so they cannot undergo acylation reactions.
The acylation reaction for aliphatic amines can be generally expressed as follows.

If done with acetyl chloride or acetic anhydride as acylating agents, the reaction will be called acetylation reaction as an acetyl group $\left( {{\text{C}}{{\text{H}}_{\text{3}}}{\text{CO - }}} \right)$ is introduced into the molecule.
Similarly, acetylation with acetyl chloride of aromatic amines can also be carried out, but in presence of a catalyst like pyridine. Pyridine is a stronger base than the amine and so it removes hydrochloric acid formed during the reaction and shifts the equilibrium in forward direction. With acetic anhydride, acetylation is done either in presence of catalyst or in presence of acetic acid as catalyst.
Thus, aniline being an aromatic primary amine can be converted into N-phenylethanamide by acetylation with acetyl chloride.

Note:
Benzoylation of aromatic amines is however, carried out in presence of aqueous sodium hydroxide solution.

The benzoylation of compounds containing an active hydrogen atom such as amines, alcohols, phenols etc. with benzoyl chloride in presence of dilute aqueous sodium hydroxide solution is called the Schotten-Baumann reaction.