Alcohols can be prepared in many ways. They are prepared from alkenes by acid-catalysed hydration and by hydroboration–oxidation. Alcohols are also prepared from aldehydes and ketones by reduction. The reduction of carboxylic acids and esters also gives alcohols. Alcohols are produced by the reaction of Grignard reagents with aldehydes and ketones. Phenol, also known as carbolic acid, was first isolated in the early nineteenth century from coal tar. Nowadays, phenol is commercially produced synthetically. In the laboratory, phenols are prepared from benzene derivatives in many ways.
Which of the following is used as the catalyst in the catalytic hydrogenation of aldehydes and ketones to alcohols?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → All of the above
In catalytic hydrogenation, hydrogen adds across the C=O group of an aldehyde or ketone in the presence of a finely divided metal. Platinum, palladium and nickel are all used as this catalyst. Aldehydes give primary alcohols and ketones give secondary alcohols:
\( \displaystyle \ce{RCHO + H2} \xrightarrow{\text{Pt, Pd or Ni}} \ce{RCH2OH} \)
\( \displaystyle \ce{RCOR' + H2} \xrightarrow{\text{Pt, Pd or Ni}} \ce{RCH(OH)R'} \)
Since each of the three metals is a correct catalyst, no single metal is the full answer.
NCERT (2026-27 edition):
7.4.1 Preparation of Alcohols – “2. From carbonyl compounds
(i) By reduction of aldehydes and ketones: Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts (catalytic hydrogenation). The usual catalyst is a finely divided metal such as platinum, palladium or nickel.”