Question

Esters on reaction with $EtMgBr$ give:

• A. $1^{\circ }$ alcohols
• B. $2^{\circ }$ alcohols
• C. $3^{\circ }$ alcohols
• D. Hydroxy ketone

Answer 1

Answer: (B), (C)

The correct options are
B $2^{\circ }$ alcohols
C $3^{\circ }$ alcohols

An ester with $EtMgBr$ give mainly give tertiary alcohols except in a few cases where it gives secondary alcohols also. So, the correct answers are B and C.

Treating a formic ester with $EtMgBr$ followed by hydrolysis gives secondary alcohol whereas treating any other ester with it gives tertiary alcohol. The mechanism involves the nucleophilic attack of $EtMgBr$ on the carbonyl carbon to give an intermediate which collapses with the departure of the alkoxide ion to give the ketone or aldehyde intermediate which reacts with the second mole of $EtMgBr$.

Esters are less reactive than the intermediate ketones, therefore they themselves react with $EtMgBr$ to produce tertiary alcohols.