Question

Schiff’s reagent is:
(A) p-rosaniline hydrochloride solution decolourised with sulphurous solid
(B) Magenta solution decolourised with $\text{C}{\text{l}}_{\text{2}}$
(C) Ammoniacal silver nitrate solution
(D) Alkaline $\text{KMn}{\text{O}}_{\text{4}}$ solution

Answer 1

Hint: Alkaline $\text{KMn}{\text{O}}_{\text{4}}$solution is known as Bayer’s reagent. This pink colour reagent is used as a test of unsaturation in organic compounds. Pink colour of the reagent disappears in the presence of alkene and alkyne.
- Ammonical solution of silver nitrate is called Tollen’s reagent. This reagent is used as a confirmatory test for aldehyde. Ketones do not give this test. Appearance of a silver mirror along the side of the test tube appears due to the oxidation of aldehyde in carboxylic acid.

Complete step by step answer:
Schiff’s base is a p-rosaniline hydrochloride solution which is a pink colour solution, this solution is decolorized by $\text{S}{\text{O}}_{\text{2}}$ gas. This reagent is mainly used for the detection of carbonyl groups. Aldehyde (only aliphatic aldehyde) gives this test by giving red colour precipitate. But ketone and aromatic aldehyde do not respond to this test. Decolourisation of magenta colour of Schiff’s reagent occurs due to sulphur oxide not by chlorine gas.
So, the correct answer is “Option A”.

Note: Do not confuse with Schiff’s base and Schiff’s reagent. Schiff’s base is any substituted imine (for example aldimine) which is formed by the reaction of carbonyl compound (aldehydes and ketone) with primary amine, while Schiff’s reagent is p-rosaniline hydrochloride solution.