Question Details

Phenolic group can be identified by a positive

Options

A

Phthalein test

B

Lucas test

C

Carbylamine test

D

Tollen’s test

Correct Answer :

Phthalein test

Solution :

The correct option is Phthalein test.

Phenols containing a free para-position undergo a condensation reaction when heated with phthalic anhydride in the presence of concentrated sulfuric acid:
H2SO4
to form a dye called phenolphthalein.

When this reaction mixture is treated with a dilute sodium hydroxide solution:
NaOH
the phenolphthalein formed turns into its sodium salt, which displays a characteristic deep pink or red-violet color. This color change confirms the presence of a phenolic group.

Let us look at why the other options are incorrect:

Lucas test is used to distinguish between primary, secondary, and tertiary alcohols using a mixture of concentrated hydrochloric acid and anhydrous zinc chloride:
HCl/ZnCl2
Alcohols react at different rates to form insoluble alkyl chlorides, resulting in turbidity.

Carbylamine test is used to detect primary aliphatic and aromatic amines, which produce a foul-smelling substance called isocyanide (carbylamine).

Tollen's test is used to identify aldehydes, which reduce Tollen's reagent to produce a shiny silver mirror.

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