Question

Aldehydes are reduced to the corresponding alcohols by the addition of hydrogen in the presence of catalysts to form ____________.

Options

• None of these

• secondary alcohols

• tertiary alcohols

• primary alcohols

Answer 1

Aldehydes are reduced to the corresponding alcohols by the addition of hydrogen in the presence of catalysts to form primary alcohols.

Explanation:

\[\ce{RCHO + H2 -> RCH2OH}\]

• Aldehydes and ketones are most readily reduced with hydride reagents.
• The reducing agents LiAlH₄ and NaBH₄ act as a source of 4 x H⁻ (hydride ion)
• Overall 2 H atoms are added across the C=O to give H-C-O-H
• Hydride reacts with the carbonyl group, C=O, in aldehydes or ketones to give alcohols.
• The substituents on the carbonyl dictate the nature of the product alcohol.
• Reduction of methanal (formaldehyde) gives methanol.
• Reduction of other aldehydes gives primary alcohol.
• Reduction of ketones gives secondary alcohol.