Question

How can you prepare ethylamine by:
(a) Hoffman bromamide reaction
(b) Gabriel phthalimide reaction

Answer 1

Hint:Ethylamine is an example of a primary amine. Amines can be prepared by different methods like Gabriel pthalimide method, Hoffman bromamide reaction, reaction of alkyl halides with ammonia and some reduction reactions.

Complete step by step solution:
(a) Primary amines can be prepared from compounds having amine group and a carbonyl group. This reaction is used for making one carbon less in the product than the original reactant.
Primary amides are used for this reaction. When primary amides react with aqueous or ethanolic potassium hydroxide and bromine, a primary amine, which has one carbon less than the primary amide taken, is obtained. The general reaction is given below:
${{R}} - {{CON}}{{{H}}_2} + {{B}}{{{r}}_2} + 4{{KOH}} \to {{R}} - {{N}}{{{H}}_2} + {{{K}}_2}{{C}}{{{O}}_3} + 2{{KBr}} + 2{{{H}}_2}{{O}}$
Ethylamine can be prepared by the following reaction:
${{C}}{{{H}}_3}{{C}}{{{H}}_2} - {{CON}}{{{H}}_2} + {{B}}{{{r}}_2} + 4{{KOH}} \to {{C}}{{{H}}_3}{{C}}{{{H}}_2} - {{N}}{{{H}}_2} + {{{K}}_2}{{C}}{{{O}}_3} + 2{{KBr}} + 2{{{H}}_2}{{O}}$
Aromatic primary amines cannot be formed using this type of reaction. This is because it is a nucleophilic substitution reaction. Nucleophilic substitution reaction does not occur in aryl halides. But aromatic primary amines can be prepared from aryl amides.

Note:
Hoffman bromamide reaction is applicable for both aliphatic and aromatic compounds. Potassium hypobromite can also be used as a reagent in this reaction.
Secondary and tertiary amines do not give positive results for Gabriel phthalimide reactions.