Amines

Amines

Question

Describe the following giving the relevant chemical equation in each case:

(i) Carbylamines reaction

(ii) Hofmann’s bromamide reaction.

Answer

(i) Carbylamines reaction

Carbylamines reaction is used as a test for the identification of primary amines. When aliphatic and aromatic primary amines are heated with chloroform and ethanolic potassium hydroxide, carbylamines (or isocyanides) are formed. These carbylamines have very unpleasant odours.

Secondary and tertiary amines do not respond to this test.

 stack straight R minus NH subscript 2 with Primary space amine below space plus stack CHCl subscript 3 with chloroform below space plus stack 3 space KOH space with potassium space hydroxide below left parenthesis alc. right parenthesis space rightwards arrow with increment on top space space stack straight R minus NC with carbylamine below space plus space 3 space KCl space plus 3 space straight H subscript 2 straight O

For example, 

 CH subscript 3 minus NH subscript 2 space plus CHCl subscript 3 space plus 3 KOH space left parenthesis alc. right parenthesis space rightwards arrow with space increment space space on top space stack CH subscript 3 minus NC with methyl space carbylamine below space plus 3 KCl space plus 3 space straight H subscript 2 straight O

(b) Hoffmann bromamide reaction

When an amide is treated with bromine in an aqueous or ethanolic solution of sodium hydroxide, a primary amine with one carbon atom less than the original amide is produced. This degradation reaction is known as Hoffmann bromamide reaction. This reaction involves the migration of an alkyl or aryl group from the carbonyl carbon atom of the amide to the nitrogen atom.

 stack straight R minus CO minus NH subscript 2 with amide below space plus Br subscript 2 space plus 4 NaOH space rightwards arrow stack straight R minus NH subscript 2 with primary space amine below space plus Na subscript 2 CO subscript 3 space plus 2 NaBr space plus straight H subscript 2 straight O

For space example comma

stack CH subscript 3 minus CO minus NH subscript 2 with Ethanamide below space plus Br subscript 2 plus 4 NaOH space rightwards arrow space stack CH subscript 3 minus NH subscript 2 with Methanamine below space plus Na subscript 2 CO subscript 3 space plus 2 NaBr space plus 2 straight H subscript 2 straight O

stack straight C subscript 6 straight H subscript 5 minus CO minus NH subscript 2 with Benzamide below space plus Br subscript 2 plus 4 NaOH space rightwards arrow space stack straight C subscript 6 straight H subscript 5 minus NH subscript 2 with aniline below space plus Na subscript 2 CO subscript 3 space plus 2 NaBr space plus 2 straight H subscript 2 straight O

 

 

 

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