Question

A simple chemical test to distinguish between benzoic acid & cinnamic acid

Answer 1

Bromine test [ Reagent- Br2/CH3COOH ]

Benzoic acid will not de-colorise red bromine as addition of bromine will not happen on the benzene ring

The cinnamic acid will de-colorise red bromine and form a vicinal dibromide after addition of bromine on the pi bond ( the product is included in the attachment )

Also any simple test for a π bond will distinguish between the two as at nominal conditions benzene doesn't undergo addition reactions

Answer 2

Bromine test is used to distinguish between benzoic acid & cinnamic acid.

• Bromine water is red.
• To distinguish between benzoic acid and cinnamic acid bromine water is added to it.
• Benzoic acid does not react with bromine water and can not decolourise the red colour of bromine water.
• Cinnamic acid is an unsaturated compound. So, it easily reacts with bromine and decolourises the red colour of bromine water.