Qualitative tests for Carboxylic Acids, Amide and Esters

Contents

• Qualitative tests for carboxylic acids

• Qualitative tests for amide

• Qualitative tests for esters

Learning Objectives

At the end of this lecture, student will be able to

• Explain the qualitative tests for carboxylic acids

• Explain the qualitative tests for amides

• Explain the qualitative tests for esters

Qualitative tests for carboxylic acids

• Litmus test- Carboxylic acid turns blue litmus red

Sodium Hydrogen Carbonate Test

• Carboxylic acids reacts with sodium hydrogen carbonate to produce carbon dioxide gas which can be seen in the form of a brisk effervescence

Ester Test

• Carboxylic acid reacts with alcohol in presence of conc. sulphuric acid to form ester that is identified by the presence of a fruity smell.

Qualitative tests for amides

• Amides are decomposed by NaOH to evolve ammonia. The gas can be tested by a moist red litmus paper which is then turned blue

Alkaline hydrolysis of aromatic amides to aromatic acid

• The soluble sodium salt of aromatic acid formed from aromatic amides upon hydrolysis is regenerated as white precipitate in acidic medium.

Hydroxamic acid test for aromatic primary amides:

• Hydrogen peroxide reacts with aromatic primary amides to form the hydroxamic acid, which then reacts with ferric chloride to form ferric hydroxamate complex having a violet colour.

Qualitative tests for esters

Hydroxamic acid test

• Esters react with hydroxylamines to yield hydroxamic acids which in their turn form a wine red ferric hydroxamate with ferric ions

Note

• Hydrochloric acid and acid anhydrides also form hydroxamic acids under the described conditions.

• They can be converted into salts, though, by the action of NaOH on slight warming. As salts they cannot react to hydroxamic acids

Summary

Qualitative tests for carboxylic acids

• Sodium hydrogen carbonate test

• Ester test

Qualitative tests for amide

• Alkaline hydrolysis

• Hydroxamic acid test

Qualitative tests for esters

• Hydroxamic acid test