Question

p-Cresol reacts with chloroform in alkaline medium to give the compound A which adds hydrogen cyanide to form the compound B. The latter on acidic hydrolysis gives chiral carboxylic acid. The structure of the carboxylic acid is

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Reaction of p-Cresol with chloroform in alkaline medium is a Riemer-Tiemann reaction in which a $CHO$ group is added to the ortho position of the $OH$ group in the substrate. Here, the reaction indermediate is dichlorocarbene which undergo electrophilic substitution followed by hydrolysis to give the product 'A'. Product 'A' on reacting with $HCN$ will undergo nucleophilic addition to form a cyanohydrin product 'B'.
We know, hydrolysis of $CN$ will give $COOH$.
Hence, product 'B' on hydrolysis gives carboxylic acid product which is chiral.


General mechanism of Riemer-Tiemann reaction :
The mechanism of Riemer-Tiemann reaction involves 3 steps.

Step-1:
Formation of carbene

Step-2:
Formation of intermediate

Step-3:
Hydrolysis of intermediate