medium difficulty7 min

Preparation Methods of Amines

Amines can be prepared by reducing nitrogen-containing functional groups or by named reactions that introduce an amino group under controlled conditions.

In one line: Nitrile keeps its carbon; Hofmann loses the carbonyl carbon.

Practice This Concept

Understand it

Important preparations include reduction of nitro compounds to primary amines, reduction of nitriles to primary amines with one extra carbon in the chain, reduction of amides using LiAlH₄, Hofmann bromamide degradation of amides to primary amines with one fewer carbon atom, and Gabriel phthalimide synthesis for primary aliphatic amines. Each method must be remembered with its reagent role and carbon-count effect.

Example

Nitrobenzene gives aniline on reduction, while ethanamide gives methylamine in Hofmann bromamide reaction because one carbon is lost.

Rule to remember

Key patterns: RNO2 + reduction gives RNH2; RCN + reduction gives RCH2NH2; RCONH2 + Br2/KOH gives RNH2 with one fewer carbon than the amide.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Convert ethanamide to methanamine.

1Use Hofmann bromamide reaction with Br₂ and KOH.
2CH₃CONH₂ gives CH₃NH₂, so the product has one carbon instead of two.

Method you can reuse

1First identify the starting functional group: nitro, nitrile, amide, or haloalkane route.
2Then choose the reagent, check whether carbon count is retained, increased, or decreased, and write the amine product.

Visual tip

A flow chart of substrate to reagent to product is useful for revision, especially to compare carbon count changes.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Which amine is obtained from propanamide by Hofmann bromamide reaction?

Think first, then show answer

Ethylamine is obtained because the amide loses the carbonyl carbon during Hofmann bromamide degradation.

Common wrong answer

Writing ethylamine from ethanamide in Hofmann bromamide reaction.

Why it loses marks: The carbonyl carbon is removed.

Don't mix this up

A common error is forgetting that Hofmann bromamide reaction shortens the carbon chain by one carbon, while nitrile reduction gives an amine with the nitrile carbon retained.

Exam tip

Track carbon count before writing the product; many preparation questions are designed around chain length change.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions ask for reagent identification, product prediction, named reaction writing, conversion routes, and reasons why Gabriel synthesis is suitable mainly for primary aliphatic amines.

1
Enough for 1 mark
Amines can be prepared by reducing nitrogen-containing functional groups or by named reactions that introduce an amino group under controlled conditions.
2
Add for 2 marks
Example: Nitrobenzene gives aniline on reduction, while ethanamide gives methylamine in Hofmann bromamide reaction because one carbon is lost.
3
Add for 3 marks
Important preparations include reduction of nitro compounds to primary amines, reduction of nitriles to primary amines with one extra carbon in the chain, reduction of amides using LiAlH₄, Hofmann bromamide degradation of amides to primary amines with one fewer carbon atom, and Gabriel phthalimide synthesis for primary aliphatic amines.

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