medium difficulty6 min

Major Reactions of Carboxylic Acids

Carboxylic acids undergo reactions such as esterification, reduction, alpha-halogenation through the HVZ reaction, and decarboxylation under suitable conditions.

In one line: Carboxylic acid reactions answer four questions: ester, alcohol, alpha-halogen, or CO₂ loss.

Practice This Concept

Understand it

Carboxylic acid reactions are best understood by recognising which bond or position is changing.
In esterification, the -OH of the acid is involved in forming an ester with an alcohol under acid catalysis.
Strong reducing agents such as LiAlH₄ convert carboxylic acids to primary alcohols.
The HVZ reaction halogenates the alpha carbon of carboxylic acids that have alpha hydrogen.
Decarboxylation removes carbon dioxide from carboxylate salts under suitable heating conditions.

Example

Ethanoic acid reacts with ethanol in the presence of concentrated acid to form ethyl ethanoate. Ethanoic acid on reduction with LiAlH₄ gives ethanol.

Rule to remember

Esterification: RCOOH + R'OH in acid catalysis → RCOOR' + H₂O.

Reduction: RCOOH + LiAlH₄ → RCH2OH.

HVZ: RCH2COOH + X2/red P → RCHXCOOH.

Decarboxylation: carboxylate salt under suitable conditions → hydrocarbon with one less carbon.

See it worked out

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

Worked example

1Convert propanoic acid to 2-bromopropanoic acid.
2Propanoic acid has alpha hydrogen, so treat it with bromine in the presence of red phosphorus under HVZ conditions to replace an alpha hydrogen by bromine.

Method you can reuse

Locate the -COOH group, identify the requested product class, check alpha hydrogen if HVZ is involved, select the reagent, then verify carbon count and functional group change.

Visual tip

A reaction summary map is useful to connect -COOH with ester, alcohol, alpha-halo acid, and decarboxylation product.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

What product is formed when CH₃COOH is reduced with LiAlH₄?

Think first, then show answer

Ethanol is formed because LiAlH₄ reduces the -COOH group to -CH2OH.

Common wrong answer

Writing aldehyde as the final product of LiAlH₄ reduction of a carboxylic acid; the usual product is a primary alcohol.

Don't mix this up

Students often apply HVZ reaction to acids without alpha hydrogen, where the required alpha-halogenation cannot occur.

Exam tip

Before writing a carboxylic acid reaction, check whether the question asks for ester formation, reduction to alcohol, alpha substitution, or loss of CO₂.

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

Asked as conversions, reagent identification, named reaction, product prediction, and reason questions about alpha hydrogen or reduction products.

1
Enough for 1 mark
Carboxylic acids undergo reactions such as esterification, reduction, alpha-halogenation through the HVZ reaction, and decarboxylation under suitable conditions.
2
Add for 2 marks
Example: Ethanoic acid reacts with ethanol in the presence of concentrated acid to form ethyl ethanoate. Ethanoic acid on reduction with LiAlH₄ gives ethanol.
3
Add for 3 marks
Carboxylic acid reactions are best understood by recognising which bond or position is changing.

MCQ Quiz

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