Saved Bookmarks
| 1. |
Give preparation of alcohols from aldehydes and ketones. |
|
Answer» Solution :`to` The alcohols can be prepared from aldehyde and ketones by : `to` (i) REACTION with the Grignard reagent (R - MgX) : By this method, all three types of alcohols i.e., primary, secondary and tertiary alcohols can be prepared. Methanal always produces primary alcohol, aldehyde except methanal produces secondary alcohols whereas ketone always produces tertiary alcohols.  Mechanism of the reaction : The first step of the reaction is the NUCLEOPHILIC addition reaction of Grignard reagent to the carbonyl group to form a tetrahedral intermediate. The hydrolysis of intermediate produces alcohols.  (ii) REDUCTION of aldehydes and ketones : In a PRESENCE of reducing agents such as `LiAlH_(4) //H_(2)O [LAH]` or `NaBH_(4)//H_(2)O` or by addition of `H_(2)` in presence of finely divide metals such as Pt or Pd or Ni (Catalytic hydrogenation), the aldehyde and ketone reduces to alcohols. The reduced product of aldehyde is primary alcohol and that of ketone is a secondary alcohol. `RCHO + H_(2) overset(Pd)to RCH_(2)OH` `RCOR. overset(NaBH_(4))to R -underset(OH)underset(|)CH- R.` |
|