Question

How will you obtain butan – 2 – ol from:
i)Propanal
ii) Butan – 2 – one
iii) But – 2 – ene

Answer 1

Hint: butan – 2 – ol is a secondary alcohol, which has OH group attached with two carbon atoms. The secondary alcohols can be prepared by aldehydes, ketones and even alkenes. The process of conversion includes reaction with Grignard reagent, reduction reaction and acid catalyzed hydration reaction.

Complete answer:
We have been given to prepare butan – 2 – ol from propanal, butan – 2 – one and but – 2 – ene. These reactions will be carried out by different reagents that will result in the formation of secondary alcohol that is butan – 2 – ol.
i)Propanal
The reaction includes Grignard reagent, which attacks the carbonyl part of the propanal which results in an intermediate, this on hydrolysis results in butan – 2 – ol. The reaction is as follows:
ii) Butan – 2 – one
Butan – 2 – one is a ketone, the reduction of ketone results in alcohol. So, lithium aluminum hydride is used as a reducing agent that converts butan – 2 – one into butan – 2 – ol. The reaction is:
iii) But – 2 – ene
The alkenes are converted to alcohols by acid catalyzed hydration; this involves a mechanism of Markovnikov’s rule, where the negative part of the addendum goes to that carbon of double bond having less number of hydrogen atoms. The reaction is as follows:

Note:
Grignard reagent is an organic compound having metal and halide. Formaldehyde when reacts with Grignard reagent yields primary alcohol, while other aldehydes on reaction with Grignard reagent gives secondary alcohols. Lithium aluminum hydride is a strong reducing agent that can convert carboxylic acids into alcohols.