Question

Which of the following compound can be obtained in above reaction?

• A. Propanone
• B. 2-pentanone
• C. 3-pentanone
• D. 2-pentanol

Answer 1

Answer: (C)

3-pentanone

Answer 2

The starting material is a cyclic carbonate. Reaction with excess ethyl magnesium halide (EtMgX), a Grignard reagent, followed by hydrolysis, leads to the formation of a ketone. The reaction mechanism involves the attack of the Grignard reagent on the carbonyl carbon, followed by ring opening and elimination of the alkoxy group. For the formation of 3-pentanone (CH3CH2COCH2CH3), the carbonyl carbon must be substituted by two ethyl groups. This can be achieved if the starting material is an ester that, upon reaction with EtMgX, leads to the formation of a ketone. In this specific case, the cyclic carbonate reacts with EtMgX to form 3-pentanone.