Preparation of alcohols from Aldehydes and ketones

Aldehydes and ketones are converted into alcohols by different methods, they are
1. Reduction
2. Using Grignard reagent

Reduction

Aldehydes and Ketones are reduced to the corresponding alcohols by
1. Addition of hydrogen in the presence of catalysts (catalytic hydrogenation), such as finely divided platinum, palladium, nickel and ruthenium

2. Treating aldehydes and ketones with chemical reagents such as sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4). Aldehydes yield primary alcohols while ketones give secondary alcohols.

R – CHO (Aldehyde) + H2 ----pd------> R CH2OH (primary alcohol)

CH3CHO (Acetaldehyde) + H2 ----Ni------> CH3CH2OH (Ethanol)

R CO R’ (Ketone) -----^1.NaBH4,_2.H2O---> R – CH –R’–OH (secondary alcohol)




UsIng Grignard reagent

When Grignard reagent are treated with aldehydes or ketones, addition products (magnesium salt) are formed. These products on hydrolysis give alcohols. The overall result is to blind the alkyl group of Grignard reagent to carbon of the carbonyl group and hydrogen to oxygen.
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While formaldehyde gives primary alcohols other aldehydes give secondary alcohols and ketones yield tertiary alcohols.