Question

why can sodium borohydride be preferred in reduction to alcohols over H2/Pt?

Answer 1

Sodium borohydride is a good reducing agent. Although not as powerful as lithium aluminum hydride (LiAlH₄), it is very effective for the reduction of aldehydes and ketones to alcohols. By itself, it will generally not reduce esters, carboxylic acids, or amides (although it will reduce acyl chlorides to alcohols). It is also used in the second step of the oxymercuration reaction to replace mercury (Hg) with H.

In the laboratory, aldehydes and ketones are reduced with metal hydrides (e.g. lithium aluminum hydride (LiAlH₄ ) or sodium borohydride (NaBH₄ )) to the corresponding alcohols. In industry, aldehydes and ketones are reduced to alcohols by hydrogenation using metal catalysts (nickel, palladium or platinum).

Example:

Reduction of acetone to propane-2-ol with sodium borohydride

NaBH₄ also makes an appearance in the oxymercuration reaction. Specifially, NaBH₄ is used in the second step of the reaction, to break the C-Hg bond and turn it into a C-H bond.