Alcohols, Phenols and Ethers · Question 17

An organic compound (X) with molecular formula C3H6O is not readily oxidised. On reduction it gives C3H8O (Y) which reacts with HBr to give a bromide (Z) which is converted to Grignard reagent. This Grignard reagent on reaction with (X) followed by hydrolysis gives 2,3-dimethylbutan-2-ol. Compounds (X), (Y) and (Z) respectively are:

1. CH3CH2CHO, CH3CH2CH2OH, CH3CH2CH2Br
2. CH3COCH3, CH3CH(OH)CH3, CH3CH(Br)CH3
3. CH3COCH3, CH3CH2CH2OH, CH3CH(Br)CH3
4. CH3CH2CHO, CH3CH=CH2, CH3CH(Br)CH3

Answer

(2) CH3COCH3, CH3CH(OH)CH3, CH3CH(Br)CH3

Solution

C3H6O not readily oxidised a ketone: X = CH3COCH3 (propanone).

Reduction: CH3COCH3 [H] CH3CH(OH)CH3 (Y, propan-2-ol, C3H8O)

CH3CH(OH)CH3 HBr CH3CH(Br)CH3 (Z, 2-bromopropane)

CH3CH(Br)CH3 Mg, dry ether (CH3)2CHMgBr

(CH3)2CHMgBr + CH3COCH3 (CH3)2CH-C(OMgBr)(CH3)2

H2O/H+ (CH3)2CH-C(OH)(CH3)2 (2,3-dimethylbutan-2-ol)

X, Y, Z = CH3COCH3, CH3CH(OH)CH3, CH3CH(Br)CH3

Answer: (2)